Computerize-Professional Accounting
Course Duration- 1 Year’s and 6 months’
Course Semesters
These are three Semesters-
1. First Semester- Computer Basic, Word-Processing, Spreadsheet, Internet
2. Second Semester- Manual Accounting
3. Third Semester- Computerize Accounting
a. Business’s Transaction
b. Company Management
Part-1
The Business Management
Introduction
In all activities (whether business activities or non-business activities) and in all organizations (whether business organizations like a manufacturing entity or trading entity or non-business organizations like schools, colleges, hospitals, libraries, clubs, temples, political parties) which require money and other economic resources, accounting is required to account for these resources. In other words, wherever money is involved, accounting is required to account for it. Accounting is often called the language of business. The basic function of any language is to serve as a means of communication. Accounting also serves this function.
Book- Keeping
Meaning
Book- keeping includes recording of journal, posting in ledgers and balancing of accounts. All the records before the preparation of trail balance is the whole subject matter of book- keeping. Thus, book- keeping many be defined as the science and art of recording transactions in money or money’s worth so accurately and systematically, in a certain set of books, regularly that the true state of businessman’s affairs can be correctly ascertained. Here it is important to note that only those transactions related to business are recorded which can be expressed in terms of money.
Objectives Of Book- Keeping
1. Book- keeping provides a permanent record of each transactions.
2. Soundness of a firm can be assessed from the records of assets and abilities on a particular date.
3. Entries related to incomes and expenditures of a concern facilitate to know the profit and loss for a given period.
4. It enables to prepare a list of customers and suppliers to ascertain the amount to be received or paid.
5. It is a method gives opportunities to review the business policies in the light of the past records.
6. Amendment of business laws, provision of licenses, assessment of taxes etc., are based on records.
Accounting
Meaning Of Accounting
Accounting, as an information system is the process of identifying, measuring and communicating the economic information of an organization to its users who need the information for decision making. It identifies transactions and events of a specific entity. A transaction is an exchange in which each participant receives or sacrifices value (e.g. purchase of raw material). An event (whether internal or external) is a happening of consequence to an entity (e.g. use of raw material for production). An entity means an economic unit that performs economic activities.
Objective Of Accounting
Objective of accounting may differ from business to business depending upon their specific requirements. However, the following are the general objectives of accounting.
1. To keeping systematic record: It is very difficult to remember all the business transactions that take place. Accounting serves this purpose of record keeping by promptly recording all the business transactions in the books of account.
2. To ascertain the results of the operation: Accounting helps in scertaining result i.e., profit earned or loss suffered in business during a particular period. For this purpose, a business entity prepares either a Trading and Profit and Loss account or an Income and Expenditure account which shows the profit or loss of the business by matching the items of revenue and expenditure of the same period.
3. To ascertain the financial position of the business: In addition to profit, a businessman must know his financial position i.e., availability of cash, position of assets and liabilities etc. This helps the businessman to know his financial strength. Financial statements are barometers of health of a business entity.
4. To portray the liquidity position: Financial reporting should provide information about how an enterprise obtains and spends cash, about its borrowing and repayment of borrowing, about its capital transactions, cash dividends and other distributions of resources by the enterprise to owners and about other factors that may affect an enterprise’s liquidity and solvency.
5. To protect business properties: Accounting provides upto date information about the various assets that the firm possesses and the liabilities the firm owes, so that nobody can claim a payment which is not due to him.
6. To facilitate rational decision – making: Accounting records and
7. financial statements provide financial information which help the business in making rational decisions about the steps to be taken in respect of various aspects of business.
8. To satisfy the requirements of law: Entities such as companies, societies, public trusts are compulsorily required to maintain accounts as per the law governing their operations such as the Companies Act, Societies Act, and Public Trust Act etc. Maintenance of accounts is also compulsory under the Sales Tax Act and Income Tax Act.
Importance Of Accounting
1. Owners: The owners provide funds or capital for the organization. They possess curiosity in knowing whether the business is being conducted on sound lines or not and whether the capital is being employed properly or not. Owners, being businessmen, always keep an eye on the returns from the investment. Comparing the accounts of various years helps in getting good pieces of information.
2. Management: The management of the business is greatly interested in knowing the position of the firm. The accounts are the basis, the management can study the merits and demerits of the business activity. Thus, the management is interested in financial accounting to find whether the business carried on is profitable or not. The financial accounting is the “eyes and ears of management and facilitates in drawing future course of action, further expansion etc.”
3. Creditors: Creditors are the persons who supply goods on credit, or bankers or lenders of money. It is usual that these groups are interested to know the financial soundness before granting credit. The progress and prosperity of the firm, two which credits are extended, are largely watched by creditors from the point of view of security and further credit. Profit and Loss Account and Balance Sheet are nerve centres to know the soundness of the firm.
4. Employees: Payment of bonus depends upon the size of profit earned by the firm. The more important point is that the workers expect regular income for the bread. The demand for wage rise, bonus, better working conditions etc. depend upon the profitability of the firm and in turn depends upon financial position. For these reasons, this group is interested in accounting.
5. Investors: The prospective investors, who want to invest their money in a firm, of course wish to see the progress and prosperity of the firm, before investing their amount, by going through the financial statements of the firm. This is to safeguard the investment. For this, this group is eager to go through the accounting which enables them to know the safety of investment.
6. Government: Government keeps a close watch on the firms which yield good amount of profits. The state and central Governments are interested in the financial statements to know the earnings for the purpose of taxation. To compile national accounting is essential.
7. Consumers: These groups are interested in getting the goods at reduced price. Therefore, they wish to know the establishment of a proper accounting control, which in turn will reduce to cost of production, in turn less price to be paid by the consumers. Researchers are also interested in accounting for interpretation.
8. Research Scholars: Accounting information, being a mirror of the financial performance of a business organization, is of immense value to the research scholar who wants to make a study into the financial operations of a particular firm. To make a study into the financial operations of a particular firm, the research scholar needs detailed accounting information relating to purchases, sales, expenses, cost of materials used, current assets, current liabilities, fixed assets, long-term liabilities and share-holders funds which is available in the accounting record maintained by the firm.
Functions Of Accounting
1. Record Keeping Function: The primary function of accounting relates to recording, classification and summary of financial transactions-journalisation, posting, and preparation of final statements. These facilitate to know operating results and financial positions. The purpose of this function is to report regularly to the interested parties by means of financial statements. Thus accounting performs historical function i.e., attention on the past performance of a business; and this facilitates decision making programme for future activities.
2. Managerial Function:Decision making programme is greatly assisted by accounting. The managerial function and decision making programmes, without accounting, may mislead. The day-to-day operations are compared with some pre-determined standard. The variations of actual operations with pre-determined standards and their analysis is possible only with the help of accounting.
3. Legal Requirement function: Auditing is compulsory in ca s e o f registered firms. Auditing is not possible without accounting. Thus accounting becomes compulsory to comply with legal requirements. Accounting is a base and with its help various returns, documents, statements etc., are prepared.
4. Language of Business: Accounting is the language of business. Various transactions are communicated through accounting. There are many parties-owners, creditors, government, employees etc., who are interested in knowing the results of the firm and this can be communicated only through accounting. The accounting shows a real and true position of the firm or the business.
Advantages Of Accounting
The following are the advantages of accounting to a business:
1. It helps in having complete record of business transactions.
2. It gives information about the profit or loss made by the business at the close of a year and its financial conditions. The basic function of accounting is to supply meaningful information about the financial activities of the business to the owners and the managers.
3. It provides useful information form making economic decisions,
4. It facilitates comparative study of current year’s profit, sales, expenses etc., with those of the previous years.
5. It supplies information useful in judging the management’s ability to utilise enterprise resources effectively in achieving primary enterprise goals.
6. It provides users with factual and interpretive information about transactions and other events which are useful for predicting, comparing and evaluation the enterprise’s earning power.
7. It helps in complying with certain legal formalities like filing of income-tax and sales-tax returns. If the accounts are properly maintained, the assessment of taxes is greatly facilitated.
Methods Of Accounting
Business transactions are recorded in two different ways. Single Entry and Double Entry
1. Single Entry: It is incomplete system of recording business transactions. The business organization maintains only cash book and personal accounts of debtors and creditors. So the complete recording of transactions cannot be made and trail balance cannot be prepared.
2. Double Entry: It this system every business transaction is having a two fold effect of benefits giving and benefit receiving aspects. The recording is made on the basis of both these aspects. Double Entry is an accounting system that records the effects of transactions and other events in atleast two accounts with equal debits and credits.
Steps Involved In Double Entry System
A. Preparation of Journal: Journal is called the book of original entry. It records the effect of all transactions for the first time. Here the job of recording takes place.
B. Preparation of Ledger: Ledger is the collection of all accounts used by a business. Here the grouping of accounts is performed. Journal is posted to ledger.
C. Trial Balance preparation: Summarizing. It is a summary of ledge balances prepared in the form of a list.
D. Preparation of Final Account: At the end of the accounting period to know the achievements of the organization and its financial state of affairs, the final accounts are prepared.
Advantages Of Double Entry System
1. Scientific system: This system is the only scientific system of recording business transactions in a set of accounting records. It helps to attain the objectives of accounting.
2. Complete record of transactions: This system maintains a complete record of all business transactions.
3. A check on the accuracy of accounts: By use of this system the accuracy of accounting book can be established through the device called a Trail balance.
4. Ascertainment of profit or loss: The profit earned or loss suffered during a period can be ascertained together with details by the preparation of Profit and Loss Account.
5. Knowledge of the financial position of the business: The financial position of the firm can be ascertained at the end of each period, through the preparation of balance sheet.
6. Full details for purposes of control: This system permits accounts to be prepared or kept in as much detail as necessary and, therefore, affords significant information for purposes of control etc.
7. Comparative study is possible: Results of one year may be compared with those of the precious year and reasons for the change may be ascertained.
8. Helps management in decision making: The management may be also to obtain good information for its work, specially for making decisions.
9. No scope for fraud: The firm is saved from frauds and misappropriations since full information about all assets and liabilities will be available.
Meaning Of Debit And Credit
The term ‘debit’ is supposed to have derived from ‘debit’ and the term ‘credit’ from ‘creditable’. For convenience ‘Dr’ is used for debit and ‘Cr’ is used for credit. Recording of transactions require a thorough understanding of the rules of debit and credit relating to accounts. Both debit and credit may represent either increase or decrease, depending upon the nature of account.
Types Of Account
1. The object of book-keeping is to keep a complete record of all the transactions that place in the business. To achieve this object, business transactions have been classified into three categories:
2. Transactions relating to persons.
3. Transactions relating to properties and assets
4. Transactions relating to incomes and expenses.
Personal Accounts
Accounts recording transactions with a person or group of persons are known as personal accounts. These accounts are necessary, in particular, to record credit transactions. Personal accounts are of the following types:
1. Natural persons: An account recording transactions with an individual human being is termed as a natural persons’ personal account. eg., Kamal’s account, Mala’s account, Sharma’s accounts. Both males and females are included in it
2. Artificial or legal persons: An account recording financial transactions with an artificial person created by law or otherwise is termed as an artificial person, personal account, e.g. Firms’ accounts, limited companies’ accounts, educational institutions’ accounts, Co-operative society account.
3. Groups/Representative personal Accounts: An account indirectly representing a person or persons is known as representative personal account. When accounts are of a similar nature and their number is large, it is better tot group them under one head and open a representative personal accounts. e.g., prepaid insurance, outstanding salaries, rent, wages etc.
When a person starts a business, he is known as proprietor. This proprietor is represented by capital account for all that he invests in business and by drawings accounts for all that which he withdraws from business. So, capital accounts and drawings account are also personal accounts.
The rule for personal accounts is:
i. Debit the receiver
ii. Credit the giver
Real Accounts
Accounts relating to properties or assets are known as ‘Real Accounts’, A separate account is maintained for each asset e.g., Cash Machinery, Building, etc., Real accounts can be further classified into tangible and intangible.
1. Tangible Real Accounts: These accounts represent assets and properties which can be seen, touched, felt, measured, purchased and sold. e.g. Machinery account Cash account, Furniture account, stock account etc.
2. Intangible Real Accounts: These accounts represent assets and properties which cannot be seen, touched or felt but they can be measured in terms of money. e.g., Goodwill accounts, patents account, Trademarks account, Copyrights account, etc.
The rule for Real accounts is:
1. Debit what comes in
2. Credit what goes out
Nominal Accounts
Accounts relating to income, revenue, gain expenses and losses are termed as nominal accounts. These accounts are also known as fictitious accounts as they do not represent any tangible asset. A separate account is expense or loss and gain or income. Wages account, Rent account Commission account, Interest received account are some examples of nominal account
The rule for Nominal accounts is:
Debit all expenses and losses
1. Credit all incomes and gains
2. BRANCHES OF ACCOUNTIN
The changing business scenario over the centuries gave rise to specialized branches of accounting which could cater to the changing requirements. The branches of accounting are;
1. Financial accounting;
2. Cost accounting; and
3. Management accounting. Now, let us understand these terms.
Financial Accounting
The accounting system concerned only with the financial state of affairs and financial results of operations is known as Financial Accounting. It is the original from of accounting. It is mainly concerned with the preparation of financial statements for the use of outsiders like creditors, debenture holders, investors and financial institutions. The financial statements i.e., the profit and loss account and the balance sheet, show them the manner in which operations of the business have been conducted during a specified period.
Cost Accounting
In view of the limitations of financial accounting in respect of information relating to the cost of individual products, cost accounting was developed. It is that branch of accounting which is concerned with the accumulation and assignment of historical costs to units of product and department, primarily for the purpose of valuation of stock and measurement of profits. Cost accounting seeks to ascertain the cost of unit produced and sold or the services rendered by the business unit with a view to exercising control over these costs to assess profitability and efficiency of the enterprise. It generally relates to the future and involves an estimation of future costs to be incurred. The process of cost accounting based on the data provided by the financial accounting.
Management Accounting
It is an accounting for the management i.e., accounting which provides necessary information to the management for discharging its functions. According to the Anglo-American Council on productivity, “Management accounting is the presentation of accounting information is such a way as to assist management in the creation of policy and the day-to-day operation of an undertaking.” It covers all arrangements and combinations or adjustments of the orthodox information to provide the Chief Executive with the information from which he can control the business e.g. Information about funds, costs, profits etc. Management accounting is not only confined to the area of cost accounting but also covers other areas (such as capital expenditure decisions, capital structure decisions, and dividend decisions) as well.
Bases Of Accounting
1. Accounting on Cash basis
2. Accrual Basis of Accounting or Mercantile System
3. Mixed or Hybrid Basis of Accounting
Accounting Terminology
Ø Transaction
Ø Debtor
Ø Creditor
Ø Capital
Ø Liability
Ø Asset
Ø Goods
Ø Revenue
Ø Expense
Ø Expenditure
Ø Purchases
Ø Sales
Ø Stock
Ø Drawings
Ø Losses
Ø Account
Ø Invoice
Ø Voucher
Ø Proprietor
Ø Discount
Ø Solvent
Ø Insolvent
It is necessary to understand some basic accounting terms which are daily in business world. These terms are called accounting terminology.
Ø Transaction
“An event the recognition of which gives rise to an entry in accounting records. It is an event which results in change in the balance sheet equation. That is, which changes the value of assets and equity. In a simple statement, transaction means the exchange of money or moneys worth from one account to another account Events like purchase and sale of goods, receipt and payment of cash for services or on personal accounts, loss or profit in dealings etc., are the transactions”. Cash transaction is one where cash receipt or payment is involved in the exchange.
Ø Debtor
A person who owes money to the firm mostly on account of credit sales of goods is called a debtor. For example, when goods are sold to a person on credit that person pays the price in future, he is called a debtor because he owes the amount to the firm.
Ø Creditor
A person to whom money is owing by the firm is called creditor. For example, Madan is a creditor of the firm when goods are purchased on credit from him
Ø Capital
It means the amount (in terms of money or assets having money value) which the proprietor has invested in the firm or can claim from the firm. It is also known as owner’s equity or net worth. Owner’s equity means owner’s claim against the assets. It will always be equal to assets less liabilities, say:
Capital = Assets – Liabilities.
Ø Liability
It means the amount which the firm owes to outsiders that is, excepting the proprietors. In the words of Finny and Miller, “Liabilities are debts; they are amounts owed to creditors; thus the claims of those who ate not owners are called liabilities”. In simple terms, debts repayable to outsiders by the business are known as liabilities.
Ø Asset
Any physical thing or right owned that has a money value is an asset. In other words, an asset is that expenditure which results in acquiring of some property or benefits of a lasting nature.
Ø Goods
It is a general term used for the articles in which the business deals; that is, only those articles which are bought for resale for profit are known as Goods.
Ø Revenu
It means the amount which, as a result of operations, is added to the capital. It is defined as the inflow of assets which result in an increase in the owner’s equity. It includes all incomes like sales receipts, interest, commission, brokerage etc., However, receipts of capital nature like additional capital, sale of assets etc., are not a pant of revenue.
Ø Expense
The terms ‘expense’ refers to the amount incurred in the process of earning revenue. If the benefit of an expenditure is limited to one year, it is treated as an expense (also know is as revenue expenditure) such as payment of salaries and rent.
Ø Expenditure
Expenditure takes place when an asset or service is acquired. The purchase of goods is expenditure, where as cost of goods sold is an expense. Similarly, if an asset is acquired during the year, it is expenditure, if it is consumed during the same year, it is also an expense of the year.
Ø Purchases
Buying of goods by the trader for selling them to his customers is known as purchases. As the trade is buying and selling of commodities purchase is the main function of a trade. Here, the trader gets possession of the goods which are not for own use but for resale. Purchases can be of two types. viz, cash purchases and credit purchases. If cash is paid immediately for the purchase, it is cash purchases, If the payment is postponed, it is credit purchases.
Ø Sales
When the goods purchased are sold out, it is known as sales. Here, the possession and the ownership right over the goods are transferred to the buyer. It is known as. ‘Business Turnover’ or sales proceeds. It can be of two types, viz.,, cash sales and credit sales. If the sale is for immediate cash payment, it is cash sales. If payment for sales is postponed, it is credit sales.
Ø Stock
The goods purchased are for selling, if the goods are not sold out fully, a part of the total goods purchased is kept with the trader unlit it is sold out, it is said to be a stock. If there is stock at the end of the accounting year, it is said to be a closing stock. This closing stock at the year end will be the opening stock for the subsequent year.
Ø Drawings
It is the amount of money or the value of goods which the proprietor takes for his domestic or personal use. It is usually subtracted from capital.
Ø Losses
Loss really means something against which the firm receives no benefit. It represents money given up without any return. It may be noted that expense leads to revenue but losses do not. (e.g.) loss due to fire, theft and damages payable to others,
Ø Account
It is a statement of the various dealings which occur between a customer and the firm. It can also be expressed as a clear and concise record of the transaction relating to a person or a firm or a property (or assets) or a liability or an expense or an income.
Ø Invoice
While making a sale, the seller prepares a statement giving the particulars such as the quantity, price per unit, the total amount payable, any deductions made and shows the net amount payable by the buyer. Such a statement is called an invoice.
Ø Voucher
A voucher is a written document in support of a transaction. It is a proof that a particular transaction has taken place for the value stated in the voucher. Voucher is necessary to audit the accounts.
Ø Proprietor
The person who makes the investment and bears all the risks connected with the business is known as proprietor.
Ø Discount
When customers are allowed any type of deduction in the prices of goods by the businessman that is called discount. When some discount is allowed in prices of goods on the basis of sales of the items, that is termed as trade discount, but when debtors are allowed some discount in prices of the goods for quick payment, that is termed as cash discount.
Ø Solvent
A person who has assets with realizable values which exceeds his liabilities is insolvent.
Ø Insolvent
A person whose liabilities are more than the realizable values of his assets is called an insolvent.
Accounting Equation
As indicated earlier, every business transaction has two aspects. One aspect is debited other aspect is credited. Both the aspects have to be recorded in accounts appropriately. American Accountants have derived the rules of debit and credit through a ‘novel’ medium, i.e., accounting equation. The equation is as follows:
Assets = Equities
The equation is based on the principle that accounting deals with property and rights to property and the sum of the properties owned is equal to the sum of the rights to the properties. The properties owned by a business are called assets and the rights to properties are known as liabilities or equities of the business. Equities can be subdivided into equity of the owners which is known as capital and equity of creditors who represent the debts of the business know as liabilities. These equities may also be called internal equity and external equity. Internal equity represents the owner’s equity in the assets and external represents he outsider’s interest in the asset. Based on the bifurcation of equity, the accounting equation can be restated as follows:
Assets = Liabilities + Capital (Or) Capital = Assets – Liabilities (Or) Liabilities = Assets – Capital.
he equation is fundamental in the sense that it gives a foundation to the double entry book-keeping system. This equation holds good for all transaction and events and at all periods of time since every transaction and events has two aspects.
Part-2
JOURNAL
Introductions
When the business transactions take place, the first step is to record the same in the books of original entry or subsidiary books or books of prime or journal. Thus journal is a simple book of accounts in which all the business transactions are originally recorded in chronological order and from which they are posted to the ledger accounts at any convenient time. Journalsing refers to the act of recording each transaction in the journal and the form in which it is recorded, is known as a journal entry.
Advantages Of Journal
The following are the inherent advantages of using journal, though the transactions can also be directly recorded in the respective ledger accounts;
1. As all the transactions are entered in the journal chronologically, a date wise record can easily be maintained;
2. All the necessary information and the required explanations regarding all transactions can be obtained from the journal; and
3. Errors can be easily located and prevented by the use of journal or book of prime entry.
The specimen journal is as follows:
Date Particulars L.F. Debit Credit
Rs. Rs.
1 2 3 4 5
The journal has five columns, viz. (1) Date; (2) Particulars; (3) Ledger Folio;
(4) Amount (Debit); and (5) Amount (Credit) and a brief explanation of the transaction by way of narration is given after passing the journal entry.
Date: In each page of the journal at the top of the date column, the year is written and in the next line, month and date of the first entry are written. The year and month need not be repeated until a new page is begun or the month or the year changes. Thus, in this column, the date on which the transaction takes place is alone written.
Particulars: In this column, the details regarding account titles and description are recorded. The name of the account to be debited is entered first at the extreme left of the particulars column next to the date and the abbreviation ‘Dr.’ is written at the right extreme of the same column in the same line. The name of the account to be credited is entered in the next line preceded by the word “To” leaving a few spaces away from the extreme left of the particulars column. In the next line immediately to the account credited, a short about the transaction is given which is known as “Narration”. “Narration” may include particulars required to identify and understand the transaction and should be adequate enough to explain the transaction. It usually starts with the word “Being” which means what it is and is written within parentheses. The use of the word “Being” is completely dispense with, in modern parlance. To indicate the completion of the entry for a transaction, a line is usually drawn all through the particulars column.
Ledger Folio: This column is meant to record the reference of the main book, i.e., ledger and is not filled in when the transactions are recorded in the journal. The page number of the ledger in which the accounts are appearing is indicated in this column, while the debits and credits are posted o the ledger accounts.
Amount (Debit): The amount to be debited along with its unit of measurement at the top of this column on each page is written against the account debited.
Amount (Credit): The amount to be credited along with its unit of measurement at the top of this column on each page is written against the account credited.
Sub-Division Of Journal
When innumerable number of transactions takes place, the journal, as the sole book of the original entry becomes inadequate. Thus, the number and the number and type of journals required are determined by the nature of operations and the volume of transactions in a particular business. There are many types of journals and the following are the important ones:
1. Sales Day Book- to record all credit sales.
2. Purchases Day Book- to record all credit purchases.
3. Cash Book- to record all cash transactions of receipts as well as payments.
4. Sales Returns Day Book- to record the return of goods sold to customers on credit.
5. Purchases Returns Day Book- to record the return of goods purchased from suppliers on credit.
6. Bills Receivable Book- to record the details of all the bills received.
7. Bills Payable Book- to record the details of all the bills accepted.
8. Journal Proper-to record all residual transactions which do not find place in any of the aforementioned books of original entry.
Part-3
Ledger
Ledger is a main book of account in which various accounts of personal, real and nominal nature, are opened and maintained. In journal, as all the business transactions are recorded chronologically, it is very difficult to obtain all the transactions pertaining to one head of account together at one place. But, the preparation of different ledger accounts helps to get a consolidated picture of the transactions pertaining to one ledger account at a time. Thus, a ledger account may be defined as a summary statement of all the transactions relating to a person, asset, expense, or income or gain or loss which have taken place during a specified period and shows their net effect ultimately. From the above definition, it is clear that when transactions take place, they are first entered in the journal and subsequently posted to the concerned accounts in the ledger. Posting refers to the process of entering in the ledger the information given in the journal. In the past, the ledgers were kept in bound books. But with the passage of time, they became loose-leaf ones and the advantages of the same lie in the removal of completed accounts, insertion of new accounts and arrangement of accounts in any required manner.
Sub-Division Of Ledger
In a big business, the number of accounts is numerous and it is found necessary to maintain a separate ledger for customers, suppliers and for others. Usually, the following three types of ledgers are maintained in such big business concerns.
1. Debtors’ Ledger: It contains accounts of all customers to whom goods have been sold on credit. From the Sales Day Book, Sales Returns Book and Cash Book, the entries are made in this ledger. This ledger is also known as sales ledger.
2. Creditors’ Ledger: It contains accounts of all suppliers from whom goods have been bought on credit. From the Purchases Day Book, Purchases Returns Book and Cash Book, the entries are made in this ledger. This ledger is also known as Purchase Ledger.
3. General Ledger: It contains all the residual accounts of real and nominal nature. It is also known as Nominal Ledger.
Distinction between journal and ledger
1. Journal is a book of prime entry, whereas ledger is a book of final entry.
2. Transactions are recorded daily in the journal, whereas posting in the ledger is made periodically.
3. In the journal, information about a particular account is not found at one place, whereas in the ledger information about a particular account is found at one place only.
4. Recording of transactions in the journal is called journalising and recording of transactions in the ledger is called posting.
5. A journal entry shows both the aspects debit as well as credit but each entry in the ledger shows only one aspect.
6. Narration is written after each entry in the journal but no narration is given in the ledger.
7. Vouchers, receipts, debit notes, credit notes etc., from the basic documents form journal entry, whereas journal constitutes basic record for ledger entries.
Subsidiary Books
Introduction
Journal is subdivided into various parts known as subsidiary books or sub-divisions of journal. Each one of the subsidiary books is a special journal and a book of original or prime entry. There are no journal entries when records are made in these books. Recording the transactions in a special journal and then in the ledger accounts is the practical system of accounting which is also referred to as English System. Though the usual type of journal entries are not passed in these sub-divided journals, the double entry principles of accounting are strictly followed.
Kinds Of Subsidiary Books
There are different types of subsidiary books which are commonly used in any
1. Purchases Book
This book is used to record all credit purchases made by the business concern from its suppliers. This book is also known as ‘Purchases Books’, ‘Purchases Journal’ or ‘Invoice Book’. It contains five columns, viz., Date, Particulars, Ledger Folio, Inward Invoice Number and Amount. Whenever any credit purchase is made, the date on which the transaction has taken place is entered in the ‘Date Column’, the name of the party from whom the purchase has been made the particulars column, the inward invoice number with which the purchase has been made in the ‘inward Invoice Number Column’ and the money value of the purchase in the ‘Amount Column’. The ‘L.F. Column’ is to record the ledger folio number while posting is made.
Posting: The total of purchases book for a specified period is debited to the purchases account in the Ledger. The personal accounts are posted by crediting the individual accounts.
2. Sales books
This book is used to record all credit sales effected by the business to its customers. This book is also called as ‘Sales Book’, ‘sales Journal’ or ‘Sold Book’. It contains five columns, viz., Date, Particulars, L.F., Outward Invoice Number and Amount. When any credit sales is effected, the date is entered in the ‘Date Column’, the name of the party to whom the sale is made in the ‘Particulars Column’, the invoice number with which the sales have been effected in the ‘Out-ward Invoice Number Column’ and the money value of the sales in the ‘Amount Column’, The LF column is entered while posting is effected.
Posting: The total of the Sales Book for a specified period is credited to the Sales Account in the Ledger. The personal account is posted by debiting the individual accounts.
3. Purchases Returns Books
This book is used to record all transactions relating to the goods returned to suppliers. This book is also known as ‘Purchases Returns journal’ or ‘Returns Outward Book’, the specimen ruling of a Purchases Returns Book is given below:
4. Sales Returns Books
This book is used to record all transactions relating to goods returned by customers. This book is also known as ‘Sales Return Journal’ or ‘Returns Inwards Book’, the specimen ruling of sales returns book is given below:
5. Bills Receivable Book:
This book is used to record all the bills received by the business from its customers. It contains details regarding the name of the acceptor, date of the bill, place of payment, term of the bill, due date and the amount of the bill. The specimen ruing of a Bills Receivable Book is given below:
6. Bills Receivable Book
While posting, the individual customers’ accounts will be credited and the total of the Bills Receivable Book for a specified period will be debited to the Bills Receivable Account in the Ledger.
7. Bills Payable Book:
This book is used to record all the bills accepted by the business drawn by its creditors. It contains details regarding the name of the drawer, payee and date of acceptance, due date, place of payment, term and amount of the bill.
8. Journal Proper
This book is used to record all the residual transactions which cannot find place in any of the subsidiary books. While recording, the entries are made in the journal covering both the aspects of the transaction. The following are some of the examples of transactions which are entered in this book.
1. Opening entries and closing entries.
2. Adjusting entries
3. Transfer entries from one account to another account.
4. Rectification entries.
5. Bills of Exchange Entries
6. Credit Purchase/sale of an asset other than goods.
Cash Book
Cash Book is a sub-division of Journal recording transactions pertaining to cash receipts and payments. Firstly, all cash transactions are recorded in the Cash Book wherefrom they are posted subsequently to the respective ledger accounts. The Cash Book is maintained in the form of a ledger with the required explanation called as narration and hence, it plays a dual role of a journal as well as ledger. All cash receipts are recorded on the debit side and all cash payments are recorded on the credit side. All cash transactions are recorded chronologically in the Cash Book. The Cash Book will always show a debit balance since payments cannot exceed the receipts at any time.
Kinds of Cash Book: From the above it can be observed that the Cash Book serves as a subsidiary books as well as ledger. Depending upon the nature of business and the type of cash transactions, various types of Cash books are used. They are:
1. Single Column Cash Book
2. Two Column Cash Book or Cash Book with cash and discount columns.
3. Three Columnar Cash Book or Cash Book with cash, bank and discount columns.
4. ‘Bank’ Cash Book or Cash Book with bank and discount columns.
5. Petty Cash Book.
Basic Document For Subsidiary Books
Inward Invoice:
This is the document sent by the suppliers of goods giving details of goods sent, price, value, discount etc. It is the basis for entries in purchases book.
Outward Invoice:
This is a document sent by the firm to the customers, showing the details of goods supplied, their price and value, discounts etc., it is the basis for writing sales book.
Debit Note:
It is a simple statement sent by a person to another person showing the amount debited to the account of the latter along with a brief explanation. The debit notes are issued by a trader relating to purchase returns in order to put up his claim for abatement of his dues to the other party. Debit notes are serially numbered and are similar to invoices although they are usually printed in red ink.
Credit Note:
It is nothing but a statement sent by one person to another person showing the amount credited to the account of the latter along with a brief explanation. The credit notes are used for sales return in order to intimate related abatement and are similar to invoice although they are usually printed in red ink.
Cash Receipts and Vouchers:
These are the vouchers and receipts for cash received and paid. Entries in cash book are made on the strength of the vouchers and receipts. They are also useful for auditing purpose.
Contra Entries
For any single transaction the same account cannot be debited and credited. But since cash and bank accounts are maintained in the cash book, the debit and credit may be found in the two different accounts in the Cash Book. They are transactions which affect both the sides of the Cash Book. For instance, when cash is deposited into the bank, bank account should be debited and cash account should be credited. Hence, on the debit side of the Cash Book. ‘To Cash’ is written in the particulars column and the amount is entered in the bank column. Similarly, on the credit side of the Cash Book, ‘By Bank’ is written in the particulars column and the amount is entered in the cash column.
When cash is withdrawn from the bank, on the debit side of the Cash Book, ‘To Bank’ is written in the particulars column and the amount is written in the cash column. Likewise, on the credit side of the Cash Book, ‘By Cash’ is written in the particulars column and amount is entered in the bank column. Therefore, those entries which appear on both the sides of the Cash Book are called Contra Entries and they are identified and denoted in the Cash Book itself by writing the letter ‘C’ in the Ledger Folio Columns on either side. For double entry procedure is completed in the cash book itself, no further positing is made in the ledger.
In a three columnar Cash Book, cash and bank columns are balanced as any other ledger account and discount columns are imply totaled. To know the balance of the discount columns, a separate account, viz., discount account is opened in the ledger. While the cash column will always show a debit balance, the bank column may show a credit balance at times. The credit balance in the bank column represents nothing but bank overdraft.
Discounts
Trade discount
When a customer buys goods regularly or buys large quantity or buys for a large amount, the seller is usually inclined to allow a concession in price. He will calculate the total price according to the list of catalogue. But after the total is arrived at, he will make a deduction 5% or 10% depending upon his business policy. This deduction is known as Trade discount.
Cash Discount
An amount which is allowed for the prompt settlement of debt arising out of a sale within a specified time and calculated on a percentage basis is known as cash discount, i.e., it is always associated with actual payment.
Difference Between Trade Discount and Cash Discount
Trade discount
Ø It is given by the manufacturer or the wholesaler to a retailer and not to others.
Ø It is allowed on a certain quantity being purchased.
Ø It is a reduction in the catalogue price of an article.
Ø It is not usually accounted for in the books since the net amount (i.e. after deducting discount) is shown.
Ø It is allowed only when there is a sale either cash or credit.
Ø It is allowed on payment being made before a certain date.
Ø It is a reduction in the amount due by a debtor.
Ø This discount must have to be accounted for in the books since it is deducted from the gross selling price.
Ø It is allowed only when there is cash receipt or cash payment including cheques.
Ø It varies from customer to customer depending on the time and period of payment.
Ø It is allowed only on condition. The dues should be paid within the stipulated time. If not, the debtor is not eligible for cash discount.
Cash discount
Ø It may be allowed by seller to any debtor.
Ø It is allowed or not allowed according to sales policy followed by a business concern.
Part-4
TRIAL BALANCE
Introduction
According to the dual aspect concept, the total of debit balance must be equal to the credit balance. It is a must that the correctness of posting to the ledger accounts and their balances be verified. This is done by preparing a trail balance.
Meaning
Trial balance is a statement prepared with the balances or total of debits and credits of all the accounts in the ledger to test the arithmetical accuracy of the ledger accounts. As the name indicates it is prepared to check the ledger balances. If the total of the debit and credit amount columns of the trail balance are equal, it is assumed that the posting to the ledger in terms of debit and credit amounts is accurate. The agreement of a trail balance ensure arithmetical accuracy only, A concern can prepare trail balance at any time, but its preparation as on the closing date of an accounting year is compulsory.
Objectives Of Preparing A Trail Balance
1. It gives the balances of all the accounts of the ledger. The balance of any account can be found from a glance from the trail balance without going through the pages of the ledger.
2. It is a check on the accuracy of posting. If the trail balance agrees, it proves:
i. That both the aspects of each transaction are recorded and
ii. That the books are arithmetically accurate.
3. It facilitates the preparation of profit and loss account and the balance sheet.
4. Important conclusions can be derived by comparing the balances of two or more than two years with the help of trail balances of those years.
Features Of Trail Balances
The following are the important features of a trail balances:
1. A trail balance is prepared as on a specified date.
2. It contains a list of all ledger account including cash account.
3. It may be prepared with the balances or totals of Ledger accounts.
4. Total of the debit and credit amount columns of the trail balance must tally.
5. It the debit and credit amounts are equal, we assume that ledger accounts are arithmetically accurate.
6. Difference in the debit and credit columns points out that some mistakes have been committed.
7. Tallying of trail balance is not a conclusive profit of accuracy of accounts.
Methods Of Preparing Trail Balance
A trail balance refers to a list of the ledger balances as on a particular date. It can be prepared in the following manner:
1. Total Method
According to this method, debit total and credit total of each account of ledger are recorded in the trail balance.
2. Balance Method
According to this method, only balance of each account of ledger is recorded in trail balance. Some accounts may have debit balance and the other may have credit balance. All these debit and credit balances are recorded in it. This method is widely used.
Part-5
Manufacturing Account
Introduction
‘Final Statements’ generally refer to two statement prepared by a business concern at the end of every accounting year. They are (I) Income statement and (2) Balance sheet. In case of trading concerns these statements are prepared under the headings ‘Trading and profit and loss account’ and ‘Balance sheet.’ In case of manufacturing concerns these statements are titled ‘Manufacturing, Trading, and Profit and Loss Account’ and ‘Balance Sheet.’ In case of Limited companies they are called ‘Profit and Loss Account’, ‘Profit and Loss appropriation account’ and ‘Balance sheet’.
Meaning Of Manufacturing Account
Manufacturing concerns which convert raw material into finished product is required to prepare manufacturing account and then prepare trading and profit and loss account. This is necessary because they have to ascertain cost of goods manufactured, gross profit and net profit.
Purpose Of Manufacturing Account
The main purpose of manufacturing account is to show:
1. Cost of goods manufactured; and
2. Major items of costs such as raw material consumed, productive wages, direct and indirect expenses of production.
Various Items Shown In Manufacturing Account
Debit side items
A. Raw material consumed- Manufacturing account starts with value of raw materials consumed, i.e., opening stock of raw materials plus Purchases and incidental expenses of purchase less closing stock of raw materials.
B. Direct wages and expenses- Direct wages and direct expenses are debited to manufacturing account. These are the wages and expenses directly identifiable with the output produced.
C. Indirect factory expenses- Expenses like factory rent, salaries, lighting, power, heat and fuel, machinery repairs, depreciation and other factory expenses are debited to manufacturing account. Total of Raw materials consumed, direct wages, direct expenses and factory expenses is the total manufacturing cost.
D. Opening work in progress- Work-in-progress is the semi finished output. Opening work-in-progress is shown on the debit side of manufacturing account. The assumption is that it is completed into finished output during the current accounting period.
E. Sale of Scrap- Scrap can be raw material scrap or indirect material scrap. It may be reduced from material cost on debit side. Alternatively it can be shown on credit side of manufacturing account, like an income.
Credit side
a. Closing work-in-progress- It represents the semi-finished output at the end of the accounting period and is credited to manufacturing account.
B. Sale of scrap- If it is direct material scrap, it can be reduced from raw material on debit side. However in the absence of specific details, the amount from sale of scrap can be credited to manufacturing account. In that case, whether it is direct material scrap or indirect factory material scrap makes no difference.
C. Cost of Finished goods manufactured- This is the balancing figure in the manufacturing account. It is transferred to trading account.
Note: The closing work-in-progress and sale of scrap may also be reduced on debit side and then credit side shows the cost of goods manufactured alone. That approach makes the above account look like a cost sheet prepared in cost A/c.
Specimen Of Manufacturing Account Is Presented Below
Manufacturing A/c for the year ended…….
To work-in-progress (opening ) | By Sale of scrap |
To Material used | By Work-in-progress (closing) |
Opening stock | By Cost of goods produced |
| transferred to trading A/c (bal. |
| fig) |
Add: Purchases |
|
Less: Closing stock |
|
To Wages |
|
To Factory expenses |
|
To Purchase expenses |
|
To Import duty |
|
To Carriage inward |
|
To Depreciation on machinery |
|
To Repairs to Machinery |
|
Part-6
Trading Account
Introduction
Trading account is prepared for an accounting period to find the trading results or gross margin of the business i.e., the amount of gross profit the concern has made from buying and selling during the accounting period. The difference between the sales and cost of sales is gross profit. For the purpose of computing cost of sales, value of opening stock of finished goods, purchases, direct expenses on purchasing and manufacturing are added up and closing stock of finished goods is reduced. The balance of this account shows gross profit or loss which is transferred to the profit and loss account.
Preparation Of Trading Account
Trading account is a ledger account. It has to be prepared in conformity with double entry principles of debit and credit.
Items shown in trading account:
Debit side
I. Opening stock: The stock at the beginning of an accounting period is called opening stock. This is the closing stock as per the last balance sheet. It includes stock of raw materials, work in progress, (where manufacturing account is not separately prepared) and finished goods. Trading account starts with opening stock on the debit side.
II. Purchases: The total value of goods purchased after deducting purchase returns is debited to trading a/c. Purchases comprise of cash purchases am credit purchases.
III. Direct expenses: Direct expenses are incurred to make the goods sale able. They include wages, carriage and freight on purchases, import duty, customs duty, clearing and forwarding charges manufacturing expenses or factor. Expenses (where manufacturing account is not separately prepared). All direct expenses are extracted from trial balance.
Items shown in trading account :
Credit side:
I. Sales: It includes both credit and cash sales. Sales returns are reduced from sales and net sales are shown on the credit side of trading account. The sales and returns are extracted from the trial balance.
II. Closing stock: Closing stock is the value of goods remaining at the end of the accounting period. It includes closing stock of raw materials, work progress (where manufacturing account is not separately prepared) and finished stock. The opening stock is ascertained from trial balance but closing stock is not a part of ledger. It is separately valued and given as an adjustment. If it is given in trial balance, it is after adjustment of opening and closing stocks in purchases. If closing stock is given in trial balance it is shown only as current asset in balance sheet. If closing stock is given outside trial balance, it is shown on credit side of trading account and also as current asset in the balance sheet
Closing Entries Relating To Trading Account
The Journal entries given below are passed to transfer the relevant ledger account balances to trading account.
For opening stock, purchases and direct expenses.
Trading A/c Dr
To Opening Stock A/c
To Purchases (Net) A/c
To Direct expenses A/c
[Being transfer of trading a/c debit side items]
For transfer of sales (after reducing sales returns)
Sales (net) A/c Dr
To Trading A/c
[Being transfer of sales to Trading A/c]
For transferring gross profit
Trading A/c Dr
To Profit & Loss A/c
[Being transfer of gross profit to P&L A/c]
For Gross Loss
Profit & Loss A/c Dr
To Trading A/c
[Being transfer of gross loss to P&L A/c]
Note: Closing stock is taken into account by an adjustment journal entry along with other adjustments.
A SPECIMEN OF TRADING ACCOUNT IS SHOWN BELOW Trading account for the year ended ……………
Particulars | Rs. | Rs. | Particulars | Rs. | Rs. |
|
|
|
|
|
|
| |
To Opening stock |
| xxx | By Sales | Xxx |
|
|
To purchases | xxx |
| Less: Returns inwards |
|
|
|
|
|
| (or) | xxx |
|
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|
|
| Sales Returns |
|
| |
Less: purchase returns | xxx | xxx | —– | xxx |
| |
|
| |||||
To Direct expenses: |
|
|
|
|
|
|
Wages |
| xxx | By closing stock |
|
|
|
Fuel & Power |
| xxx | By Gross loss c/d * |
| xxx |
|
Carriage inwards |
| xxx | (transferred to profit |
| xxx |
|
Royalty on production |
| xxx | and loss A/c) |
|
|
|
|
|
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| ||
Power |
| xxx |
|
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|
Coal water, Gas |
| xxx |
|
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Import duty |
| xxx |
|
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|
|
Consumable stores |
| xxx |
|
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|
|
Factory expenses |
| xxx |
|
|
|
|
To Gross profit c/d |
| xxx |
|
|
|
|
(transferred to profit and |
| —— |
|
| —— |
|
loss A/c) |
|
|
|
|
|
|
Part-7
Profit And Loss Account
Introductions
Profit and loss account is prepared to ascertain the net profit of the business concern for an accounting period
Preparation Of Profit And Loss Account
Profit and loss account starts with gross profit brought down from trading account on the credit side. (If gross loss, on the debit side). All the indirect expenses are debited and all the revenue incomes are credited to the profit and loss account and then net profit or loss is calculated. If incomes or credit is more, than the expenses or debit, the difference is net profit. On the other hand if the expenses or debit side is more, the difference is net loss.
Debit side:
Expenses shown on the debit side of profit and loss account are classified into two categories
Operating expenses and Non-operating expenses
A. Operating expenses: These expenses are incurred to operate the business efficiently. They are incurred in running the organisation. Operating expenses include administration, selling, distribution, finance, depreciation and maintenance expenses.
B. Non-operating expenses: These expenses are not directly associate with day today operations of the business concern. They include loss on sale of assets, extraordinary losses, etc.
Credit side
Gross profit is the first item appearing on the credit side of profit and loss account. Other revenue incomes also appear on the credit side of profit and to account. The other incomes are classified as operating incomes and non-operating incomes.
A. Operating incomes: These incomes are incidental to business and earned from usual business carried on by the concern. Examples: discount received, commission earned, interest received etc.
B. Non-operating incomes: These incomes are not related to the business carried on by the firm. Examples are profit on sale of fixed assets, refund of tax etc.
For transferring expenses to profit and loss account:
Profit and Loss A/c Dr
To expenses A/c
[Being transfer of all P&L A/c debit side items]
For transfer of incomes to profit and loss account
Incomes A/c Dr
To Profit and Loss A/c
[Being transfer of Incomes to P&L A/c]
For net profit:
P&L A/c Dr
To Capital A/ c
[Being net profit credited to capital]
For transfer of Net Loss
Capital A/c Dr
To P&L A/c
[Being net loss transferred to capital]
Note: In case of partnership, the profit or loss is divided between partners in their profit sharing ratio and credited or debited to the individual partners. In case of limited companies, Net profit or loss is transferred to the P&L Appropriation A/c for disposal.
The Specimen Of Profit And Loss Account Is Shown Below
Profit and Loss Account
For the year ended 31st March ————–
Particulars Rs. Particulars Rs.
To Gross loss b/d xxx By Gross profit b/d xxx
To Administration expenses By Dividends received xxx
Salaries xxx By Interest received xxx
Rent rates & taxes xxx By Discount received xxx
Printing & Stationery xxx By commission received xxx
Postage and Telegrams xxx By Rent received xxx
Telephone expenses xxx By Profit on sale of assets xxx
Legal charges xxx By Sundry revenue receipts xxx
Insurance xxx By Net loss transferred to xxx
capital A/c (Bal. Fig)*
Audit fees xxx
Directors fees xxx
General expenses xxx
To Selling & Distribution Expenses
Showroom expenses xxx
Advertising xxx
Commission paid to salesmen xxx
Bad debts xxx
Provision for doubtful debts xxx
Godown rent xxx
Carriage outward xxx
Upkeep of delivery vans xxx
To Depreciation and maintenance
Depreciation xxx
Repairs xxx
To Financial expenses
Interest ob borrowings xxx
Discount allowed xxx
To abnormal losses
Loss on sale of assets xxx
To Net profit transferred to capital xxx
A/c (bal.fig)
Note: *Either net profit or net loss is the balancing figure in P & L A/c
The purpose and importance of preparing profit and loss account.
To determine the future line of action
To know the net profit or loss of business To calculate different ratios
To compare the actual performance of the business with the desired one.
Part-8
Balance Sheet
Introduction
The Balance sheet comprises of lists of assets, liabilities and capital fund on a given date. It presents the financial position of a concern as revealed by the accounting records. It reflects the assets owned by the concern and the sources of funds used in the acquisition of those assets. In simple language it is prepared in such a way that true financial position is revealed in a form easily readable and more rapidly understood than would be possible from a view of the detailed information contained in the accounting records prepared during the currency of the accounting period. Balance sheet may be called a ‘statement of equality’ in which equality is established by representing values of assets on one side and values of liabilities and owners’ funds on the other side.
Title
A Balance sheet is called by different names probably due to lack of uniformity in accounting systems. Generally, the following titles are used in respect of balance sheet:
1. Balance sheet or General Balance sheet;
2. Statement of Financial position or condition;
3. Statement of assets and liabilities;
4. Statement of assets and liabilities and owners’ fund etc.
Of the above, the title ‘Balance sheet” is mostly used. The use of this title implies that data presented in it have been taken from the balances of accounts,
Classification Of Assets And Liabilities
A clear and correct understanding of the basic divisions of the assets and liabilities and the meanings which they signify and the amounts which they represent is very essential for a proper perspective of financial position of a business concern. Assets and liabilities are classified under the following major headings.
Assets:
are properties of business. They are classified on the basis of their nature. Different types of assets are as under:
1. Fixed assets: Fixed assets are the assets which are acquired and held permanently and used in the business with the objective of making profits. Land and building, Plant and machinery, Furniture and Fixtures are examples of fixed assets.
2. Current assets: The Assets assets of the business in the form of cash, debtors bank balances, bill receivable and stock are called current assets as they can be realised within an operating cycle of one year to discharge liabilities.
3. Tangible assets: Tangible assets have definite physical shape or identity and existence; they can be seen, felt and have volume such as land, cash, stock etc. Thus tangible assets can be both fixed assets and current assets.
4. Intangible assets: The assets which have no physical shape which cannot be seen or felt but have value are called intangible assets. Goodwill, patents, trade marks and licences are examples of intangible assets. They are usually classified under fixed assets.
5. Fictitious assets: Fictitious assets are not real assets. Past accumulated losses or expenses which are capitalised for the time being, expenses for promotion of organisations (preliminary expenses), discount on issue of shares, debit balance of profit and loss account etc. are the examples of fictitious assets.
6. Wasting assets: These assets are also called depleting assets. Assets such as mines, Timber forests, quarries etc. which become exhausted in value by way of excavation of the minerals, cutting of wood etc. are known as wasting assets. Such assets are usually natural resources with physical limitations.
7. Contingent assets: Contingent assets are assets, the existence, value possession of which is based on happening or otherwise of specific events. For example, if a business firm has filed a suit for a particular property now in possession of other persons, the firm will get the property if the suit is decided in its favour. Till the suit is decided, it is a contingent asset.
Liabilities
A liability is an amount which a business firm is ‘liable to pay’ legally. All the amounts which are claims by outsiders on the assets of the business are known as liabilities. They are credit balances in the ledger. Liabilities are classified into bur categories as given below.
1. Owner’s capital: Capital is the amount contributed by the owners of the business. In addition to initial capital introduced, proprietors may introduce additional capital and withdraw some amounts from business over a period of time. Owner’s capital is also called ‘net worth’. Net worth is the total fund of proprietors on a particulars date. It consists of capital, profits and interest on capital subject to reduction of drawings and interest on drawings.
2. In case of limited companies, capital refers to capital subscribed by shareholders. Net worth refers to paid up equity capital plus reserves and profits, minus losses.
3. Long term Liabilities: Liabilities repayable after specific duration of long period of time are called long term liabilities. They do not become due for payment in the ordinary ‘operating cycle’ of business or within a short period of lime. Examples are long term loans and debentures. Long term liabilities may be secured or unsecured, though usually they are secured.
4. Current liabilities: Liabilities which are repayable during the operating cycle of business, usually within a year, are called short term liabilities or current liabilities. They are paid out of current assets or by the creation of other current liabilities. Examples of current liabilities are trade creditors, bills payable, outstanding expenses, bank overdraft, taxes payable and dividends payable.
5. Contingent liabilities: Contingent liabilities will result into liabilities only if certain events happen. Examples are:
Bills discounted and endorsed which may be dishonoured, unpaid calls on investments.
PRFORMA OF BALANCE SHEET | |||
Balance Sheet as on ……… |
| ||
Liabilities | Rs. | Assets | Rs. |
Capital | xxx | Fixed assets | xxx |
Add: Net profit | xxx | Goodwill | xxx |
Add: Interest on capital | xxx | Land & Buildings | xxx |
| —— | Loose tools | xxx |
Less: Drawing | xxx | Furniture & fixtures | xxx |
Less: Int. on drawings | xxx | Vehicles | xxx |
Less: Loss if any | xxx | Patents | xxx |
|
| Trade marks | xxx |
Long term liabilities |
| Long term loans | xxx |
|
| (advances ) |
|
Loan on mortgage | xxx | Investments |
|
|
| Current assets |
|
Bank loan | xxx | Closing stock | xxx |
Current liabilities |
| Sundry debtors | xxx |
Sundry creditors | xxx | Bills receivable | xxx |
Bills payable | xxx | Prepaid expenses | xxx |
Bank overdraft | xxx | Accrued incomes | xxx |
Creditors for outstanding exp. | xxx | Cash at bank | xxx |
Income received in advance | xxx | Cash in hand | xxx |
|
| Fictitious assets |
|
| Preliminary expenses | xxx | |
Advertisement expenses | xxx | ||
Underwriting commission | xxx | ||
Discount on issue of | xxx | ||
shares |
| ||
Discount on issue of | xxx | ||
debentures |
| ||
| xxx |
| xxx |
Adjustments
On preparing Trading and profit and Loss Account, adjustments re necessary when accrual basis of accounting is followed. The following are the items for which adjustments are usually required.
1. Closing Stock- This is the stock which remained unsold in the preceding accounting period.
Trading A/c
Closing stock A/c Dr.
To Trading A/c
Balance Sheet
By Closing stock
Closing stock
2. Outstanding Expenses- Outstanding expenses refer to those expenses which have become due during the accounting period for which the final accounts have been prepared, but have not yet been paid.
Expenses A/c Dr
To Outstanding expenses, A/c
3. Prepaid Expenses- Prepaid expenses are the expenses the benefit of which has not been fully enjoyed before the end of the accounting year. They are expenses paid in advance or unexpired expenses.
Prepaid expense A/c Dr
To Expenses A/c
4. Income Earned but not received (Outstanding or accrued income)- It may often happen that certain items of income such s interest on investments, commission etc. are earned during the current accounting year, but have not been actually received by the end of the same year. Such incomes are known as outstanding or accrued incomes.
Accrued Income A/c Dr
To Income A/c
5. Income received in advance- Sometimes a portion of income received during the current year relate to the future period. Such portion of the income which belong to the next accounting period is income received in advance and is known as unexpired income.
Income A/c Dr
To Income received in advance A/c
6. Depreciation- Depreciation is the decreased in the value of an asset due to wear and tear, passage of time, obsolescence etc. It is a business expenses, though it is not paid in cash every year. It is to be debited to profit and loss account and the amount be deducted from the relevant asset in the Balance Sheet.
If depreciation is given in the Trial Balance, it is taken only on the debit side of Profit and Loss Account as its adjustment is over.
Depreciation A/c Dr.
To Concerned Assets A/c
7. Bad Debts- Any irrecoverable portion of sundry debtors is termed as bad debt. Bad debt is a loss to the business. If is given in the Trial Balance, it should be shown on the debit side of Profit and Loss Account. Bad debts given in the adjustment is to be deducted from sundry debtors in the Balance Sheet and the same is debited to the Profit and Loss Account.
Bad debts A/c Dr.
To Sundry Debtors A/c
8. Provision for doubtful debts- It is a provision created to meet any loss, if the debtors fail to pay the whole or part of the debt owed by them. The amount required for doubtful debt is kept by changing the amount to the profit and loss account.
Profit and Loss A/c Dr
To Provision for doubtful debts A/c
9. Provision for discount on debtors- Sometimes the goods are sold on credit to customers in one accounting period whereas the payment of the same is received in the next accounting period and discount is to be allowed.
Profit and Loss A/c Dr.
To Provision for discount on debtors A/c
Fundamentals of Tally
Introduction
Tally is the world’s fastest
and most powerful concurrent Multi-lingual business Accounting and Inventory Management software. Tally, designed exclusively to meet the needs of small and
medium businesses, is a fully integrated, affordable and highly reliable software. Tally is easy to buy, quick to install, and easy to learn and use. Tally is designed to automate and integrate all your business operations, such as sales, finance, purchasing, inventory, and manufacturing. With Tally, accurate, up-to date business information is literally at your fingertips anywhere. The powerful new features and blazing speed and power of Tally combined with enhanced MIS, Multi-lingual, Data Synchronization and Remote capabilities help you simplify all your business processes easily and cost-effectively.
Salient Features of Tally
A leading accounting package: The first version of Tally was released in 1988 and, through continuous development, is now recognized as one of the leading accounting packages across the world, with over a quarter million customers. Tally’s market share is more than 90%.
No accounting codes: Unlike other computerized accounting packages which require numeric codes, Tally pioneered the ‘no accounting codes’ concept. Tally users have the freedom to allocate meaningful names in plain English to their data items in the system.
Complete business solution: Tally provides a comprehensive solution to the accounting and inventory needs of a business. The package comprises financial accounting, book-keeping and inventory accounting. It also has various tools to extract, interpret and present data.
Integrated/ Non-integrated accounting and inventory: With Tally, the user is able to choose between accounting and accounting with inventory. If accounting with inventory is opted for, the user can choose whether it should be integrated or not.
Flexible and easy to use: Tally is very flexible. It mimics the human thought proc- ess, which means that Tally can adapt to any business need. Tally users need not change the way their business is run to adapt to the package.
Speed: Tally provides the capability to generate instant and accurate reports, which assists the management to take timely and correct decisions for the overall productivity and growth of the company.
Power: Tally allows the user to maintain multiple companies and with unlimited levels of classification & grouping capabilities. It also allows drill down facility from report level to transaction level.
Flexibility: Tally provides flexibility to generate instant reports for any given period (month/year) or at any point of time besides providing the facility to toggle between Accounting & Inventory reports of the same company or between companies.
Concurrent multi-lingual capability: Tally offers you the exclusive capability of maintaining your accounts in any Indian language, viewing them in another language and printing them in yet another Indian language.
Real time processing: Immediate posting & updating of books of accounts as soon as the transactions are entered, thereby facilitating instant statements & Reports. It also facilities real-time multi-user environment.
Online Help: The Tally Online Help (Alt+H) provides instant assistance on basic and advanced features or any other relevant topics of Tally.
Tally.NET: is an enabling framework which establishes a connection through which the remote user can access the Client’s data without copying / transferring the data.
Remote Access: Tally provides remote capabilities to access the data from any- where and anytime.
Control Centre: works as an interface between the user and Tally installed at differ- ent sites and enables the user to centrally configure and administer Site/User belonging to an account.
Support Centre: allows a user to directly post his support queries on the functional and technical aspects of the Product.
Functional Features of Tally
BASIC ACCOUNTING
- Complete book-keeping
- Books, registers and statements of accounts
- General ledgers
- Accounts receivable and accounts payable
- Flexible voucher numbering
- Flexible classification of account heads
- Panoramic view
- Drill-down display
- Database reporting
- Voucher and cheque printing
- Columnar reports
- Bank reconciliation
ADVANCED ACCOUNTING
- Multiple companies
- Multi-currency
- Multiple financial years
- Comparison of data using multi-columnar reporting.
- Memo vouchers
- Post-dated vouchers
- User-defined voucher types
- Sales and purchase extracts
- Cash flow statement
- Daily balances and transaction values/ Interest calculations
- Percentage-based reporting
- Ratio analysis
- Value Added Tax (VAT)
- Service Tax (ST)
- Fringe Benefit Tax (FBT)
- Tax Deducted at Source (TDS)
- Tax Collected at Source (TCS)
- Excise
- Payroll
BASIC INVENTORY
- Stock categories
- Stock query by stock group, or stock cate- gory
- Multiple godowns
- Stock transfers to godowns and branches
- Multiple stock valuation methods
- Batch-wise/Lot-wise, including expiry date handling
- Alternate units of measure and tail units.
- Tracking through receipt notes/ delivery notes/ rejections inwards/ rejections out-wards
- Additional costs incurred on purchase
- Movement/Profitability analysis Party- wise/ Item-wise/ Stock Group-wise
- Customizable sales invoices using price lists with multiple prices
- Sales and purchase order processing
ADVANCED INVENTORY
- Stock items classified as raw materials, work-in-process, finished goods
- Bill of Material with auto-adjustment of stocks
- Job-working concepts, including sub-con- tracting
- Additional cost of manufacturing with notional value and percentage
·
CENVAT
Support
Reorder levels
Stock ageing analysis
Batch related stock reports
Point of Sale (POS)
Excise/VAT/ Central Sales Tax (CST)/ Tax Collected at Source (TCS) related Inventory transactions and reports.
Technology Advantages
·
Simple and rapid installation: Tally has a
simple, menu-driven installation proce- dure. The user can install the program
files on any drive if the hard disk has partitions. The user can also specify
the name and directory location of the program files. Tally uses minimum hard
disk space in the local drive. Its installation on the local disk takes just a
few seconds.
·
Unlimited multi-user support: A multi-user version of Tally can be installed on a network, having any number of computers with different operating systems such as Win 95, 98, NT, 2000, XP and Linux.
Internal backup/ restore: Tally has an in-built, user-friendly ‘backup and restore’ option. It helps the user to take a backup of one or more companies or all companies, in a single directory, in the local hard disk, or in any external media.
· Data reliability: Tally offers reliable data. It uses a flexi-field, flexi-length, self- indexed, weighted file structure for an extremely compact and fast database. Tally is robust and even if there is a power failure or the computer is incorrectly shut down, data is not lost. Tally uses signalling quality data integrity checks, at regular levels, to ensure the complete reliability of data.
User-defined security levels: Tally offers high levels of security. Users can define multiple levels of security according to their requirements. Every authorised user in the company can have an individual password, with rights to use specific features only. The user with the administrator level password will have full access and can set controls for other users.
· Data security: Tally’s data integrity checks ensure that there are no external changes to the data. Tally also uses a binary encoding format of storage to prevent devious grouping of information.
·Tally audit: The Tally audit feature provides the user with administrator rights and the capability to check the entries made by the authorised users and alter these entries, if necessary. Once the entries are audited, Tally displays the altered entries, if a along with the name of the user, who has altered the entry, and the date and time of the alteration.
Tally Vault: Tally offers a data encryption option called TallyVault. Without the valid TallyVault password, the data cannot be accessed. Tally follows the DES (Data Encryption Standard) encryption method to safeguard the data.
Removal of data into a separate company: Tally allows users to maintain a com- pany for any number of financial years. Once the books of accounts have been completed for the earlier financial years, the user can split the company data into multiple companies as per financial periods required. Tally also has a feature to split company data. The user can specify the date from which the company has to be split and Tally will split the company to form two companies as per periods specified. Once the data has been split, the closing balance of the first period (first company) becomes the opening balance for the next period (second company).
Multi-directory for company
management:
The user can create multiple directories to store data. The data stored in
these directories can be accessed directly in Tally, by specifying the path.
Import/ Export of data: Any transaction can be exported and imported to other software after suitably altering the current structures to accept the Tally data structure. Data can also be imported to Tally by writing a TDL program. The data which is to be exported from Tally can be in XML, HTML or ASCII format.
Tally Synchronization: Synchronization is the process of exchanging Tally data between two or more locations. This process enables a branch office to send its data to the head office, over the Internet or a private network.
Graphical analysis of data: Tally provides graphical analysis of data which helps the user to perform deeper analysis. The user can generate graphical analysis reports such as Sales register, Purchase register, Ledgers, Funds flow, Cash flow, Stock Item registers and so on. This helps the management to quickly judge performance and
be better pre- pared for difficult times.
ODBC (Open Database Connectivity) compliance: It allows other programs to use data from Tally, directly. Thus, any program such as MS-Excel or Oracle, which is ODBC compliant, can use data from Tally. Data connectivity is dynamic, which means that any update in Tally is reflected in real time in other ODBC compliant
software. The user can also extract data from Tally and design his/ her own
report formats in other ODBC compliant software.
Protocol support: Tally provides protocol support for HTTP, HTTPS, FTP, SMTP, ODBC and raw sockets with data interchange formats such as XML, HTML with XML islands, SOAP and related formats. Protocol refers to a mechanism by which information (data) can be put into or taken from Tally. Formats refer to the standard for informa- tion to be generated from Tally or from other applications which can exchange data with Tally.
Direct web browser access: While working on Tally, the user can directly log on to the Tally website, provided he/ she has access to the Internet. The website lists details of all the facilities offered by Tally. The user can also download the latest release ofTally as and when it is available. The Tally website also offers Tally Chat, by which a user can communicate with a Tally representative and get required information.
Ability to preview and publish reports and documents on the Internet: Companies which want to publish reports and price lists on their website can do so directly from Tally.
E-mail Facility: Tally facilitates the mailing of any Tally report or document.
Multilingual capability: Tally is the world’s first accounting and inventory software with multilingual capability. Currently, Tally’s multilingual capability extends to 12 languages which include nine Indian languages (Hindi, Gujarati, Punjabi, Tamil, Telugu, Mar-athi, Kannada, Malayalam and Bengali), Bahasa Melayu and Bahasa Indonesia. Tally enables you to enter data in one language and have it transliterated into different languages. You can generate invoices, purchase orders or delivery
notes in the language of your choice after entering data for the same in any of the nine specified languages. Also, the phonetic keyboard allows you to spell the term phonetically based on how it sounds and Tally displays the data in the language selected after transliteration.
Point of Sale (POS) : POS is an acronym for Point of sale. Point of Sale can be a retail out- let, a check-out counter shop, or any other location where a sales transaction takes place. It is a computerized cash register which adds up the sales totals, calculates the balance to be returned to buyer and automatically adjusts the inventory level to reflect the quantity sold. The equipment required for POS to work effectively are cash registers, card readers, bar-code scanners and so on.
Payroll
Tally Payroll is integrated with accounting and benefits the user by simplifying Payroll processing and accounting. Tally Payroll enables users to set up and implement salary structures, ranging from simple to complex, as per the organization’s requirements. The user can also align and automate payroll processes and directly integrate them with main stream accounting applications. Tally Payroll also supports configurable formats for pay slip printing; flexible salary/wage, attendance, leave and overtime registers; gratuity and expat reports.
Getting Functional with Tally
Tally Start-up
Tally can be started in any of
the following ways:
Click on Start > Programs
> Tally > Tally or double click on the Tally icon on your desktop
The welcome screen Tally –
Power of Simplicity appears while the software loads. You will be ready to
explore Tally, the moment the Tally start up screen appears.
The Tally Start-up Screen
appears as shown below:
Tally
Screen Components
·
Title bar: Displays the Tally version number.
·
Horizontal button bar: Selection of
Language key, Keyboard Language and Tally Help.
·
Close button: Performs the standard Windows
Operating Systems function (Windows 95 onwards), allowing you to minimise Tally
and work on other applications. To restore Tally, click the Tally icon on the
taskbar.
·
Gateway of Tally: Displays
menus, screens, reports and accepts the choices and options which you select to
view data as required.
·
Buttons toolbar: Displays buttons which provide
quick interaction with Tally. Only buttons relevant to the current task are
visible.
·
Calculator Area: Used for Calculator functions.
·
Info Panel: Displays Version number, License
details, Configuration details.
Mouse/
Keyboard Conventions
While working with Tally, use
the following conventions.
MOUSE/
KEYBOARD CONVENTIONS
·
Click- Press the left mouse button.
·
Double-click- Press and release the left
mouse button twice, without moving the mouse pointer off the item.
·
Choose– Position
the mouse pointer on the item and click the left mouse button.
·
Select— Position
the mouse pointer on the item and double- click the left mouse button.
·
Press– Use
the keys on the keyboard in the combination shown.
·
Fn– Press
the function key.
·
Fn+ Press ALT + function key.
·
Fn– Press CTRL + function key.
Switching
between Screen Areas
When Tally first loads, the
Gateway of Tally screen displays. To toggle between this screen and the
Calculator/ ODBC server area at the bottom of the screen, press Ctrl+N or
Ctrl+M as indicated on the screen. A green bar highlights the active area of
the screen.
Quitting
Tally
·
You
can exit the program from any Tally screen, but Tally requires all screens to
be closed before it shuts down.
·
To
quit working on Tally,
·
Press
Esc until you see the message Quit? Yes or No ? Press Enter or Y, or click Yes
to quit Tally.
·
Alternatively,
to exit without confirmation, press Ctrl+Q from Gateway of Tally.
·
You
can also press Enter while the option Quit is selected from Gateway of Tally.
Creation/
Setting up of Company in Tally
The first step towards
understanding Tally is to create a company in Tally. Create a company using the
Company Creation screen.
Creation
of a Company
Go to Gateway of Tally >
Company Info. > Create Company
The Company Creation screen
displays as shown.
Each field in the Company
Creation screen is explained below. To navigate between the fields, use the
enter key or the tab key or arrow keys or the mouse.
Directory– Tally
assumes that the company is to be created in the data path given in the
Tally.INI file, which is displayed by default. This field is skipped by
default. However, you can change this path, if you want to, by using the
backspace key, so that Tally saves the data to a different directory specified
by you.
·
Name– This
specifies the name of the company as it appears in Tally. If you have several
companies to create with similar names, you will have to distinguish between
them to provide a unique name for Tally.
·
Mailing Name– The company name given in the Name field automatically appears in
this field. This can be changed according to your requirements. The correct
name of the company for mailing purposes should be entered.
·
Address– The address of the company (The
mailing name and address details are picked from here for any report such as
balance sheet and statement of accounts).
·
Statutory
Compliance for Select India from the list of countries.
·
State– Select the appropriate State from
the list of States.
·
Pin Code– Enter the PIN code of the specified
address.
·
Telephone No.- Enter the telephone number of the company.
·
E- Mail– E-mail
address will be used to e-mail documents, reports and data from Tally.
·
Mobile No.– Enter the mobile number of the
company.
·
Currency Symbol– This refers to the currency
symbol Tally will use for monetary values. By default, Tally displays Rs.
·
Maintain– Select the nature of the company
i.e, Accounts only or Accounts with Inventory.
·
Financial Year From– Specify the
Financial Year (FY) for the company. Tally considers 12 months from the date
you give here as the Financial Year. For example, if you give 1st April 2009,
your FY will be April to March – in this case, ending with 31st March 2010.
·
Books Beginning From– The date given for ‘Financial Year
From’ is automatically displayed. However, we can specify the actual date on
which the books of accounts start. In case our accounts are opened mid-way
during the financial year specified, we can enter the required date and start
the books of accounts accordingly.
·
TallyVault Password– TallyVault
is an enhanced security feature utilised to protect company data in an
encrypted form by means of a Password. The TallyVault password entered ensures
that the data is maintained permanently in an encrypted form without retaining
information of the password used. Data is not accessible without the TallyVault
password. Remember to keep this password private and known only to those who
need to know. If the password is lost, your data cannot be recovered.
·
Use Security Control– Tally has a
range of security controls, which can define the authority of various users to
access the information and to enter/ alter/delete the vouchers.
Base
Currency Information
Tally needs to know the default
currency for the company and how the amounts should be shown on the screen and
in the reports.
BASE CURRENCY INFORMATION
·
Base currency symbol– Pre-set as a default currency — Rs. (as
specified earlier).
·
Formal name– Complete name for the currency
symbol. By default, this is set to Indian Rupees.
·
Number of decimal places– By default, this is set to 2.
·
Is symbol suffixed to amounts? By default, this is set to No. For example,
in India, we place the Rs symbol in front of amounts.
·
Symbol for Decimal Portion– Enter the
decimal portion for the currency mentioned. Enter Paise.
·
Show amounts in millions? – Tally caters to currencies where the
different parts of large amounts are called by special names. By default, this
is set to No.
·
Put a space between amounts and symbol? — By
default, this is set to Yes.
·
Decimal Places for Printing Amounts in words- You can specify the number of decimal
places to print the amount in words. This number should be equal to or lesser
than the number specified in Number of Deci- mal places field.
Press Y or Enter to accept the
screen.
Working
with Multiple Companies
For a group of companies, you
can maintain the details of each company separately. You can select the company
to work with and close the company when it is not required. However, you can
also open many companies at the same time and switch between companies without
closing the application.
Exercise
to Create another Company
Before looking at how to view
and amend company details, let us create another company to experiment with.
Name your company as Indus Enterprises, Financial Year as 1 April 2009 &
Book beginning from 1 April 2009 and you may enter the company details as you
like,
To
create Indus Enterprises, follow this procedure:
1. From the buttons bar select Alt
+ F3: Create Cmp or simply press Alt + F3 to bring up the Company Info. Menu.
2. Select Create Company from the
menu to bring up the Company Creation screen.
3. Enter Indus Enterprises in the
Name field and experiment with entering other data of your choice (for example,
the address details).
4. When you have finished, Press Y
or Enter to accept the screen The Gateway of Tally screen will now appear.
Notice that Indus Enterprises
is highlighted. This indicates that it is the currently selected company from
the list of open companies.
You can now practice selecting,
closing and altering company information.
Practice
Exercise
1. Select a Company
2. Shut a Company
3. Alter a Company
To
Select a Company
1. Go to the Gateway of Tally >
Alt + F3 > Company Info. > Select Company OR Press F1.
Tally
displays the List of Companies screen. All the companies created are displayed
in an alphabetical order. Select the company name from the list given.
2. In case two or more companies
are loaded (like National Traders and Indus Enterprises), click on the company
which you need to work on so that the selected company will be highlighted and
will appear on top of the list.
To
Shut a Company
Go to the Gateway of Tally >
Alt + F3 > Company Info. > Shut Company. Select the Company which you
need to shut from the List of Companies. You can also use Alt + F1 to shut a Company
from the Gateway of Tally screen.
To
Alter Company Details
Go to the Gateway of Tally >
Alt + F3 > Company Info. > Alter. Select the company which you need to
alter from the List of Companies and press Enter to view the Company Alteration
screen. Alter the company details as required and accept the screen.
You can also access these
functions, by selecting the appropriate button from the button bar.
Account Group
Capital
Account- This
records the Capital and Reserves of the company. The ledgers that belong to
Capital Accounts are Share Capital, Partners’ Capital A/c, Proprietor’s Capital
Account and so on.
Reserves and
Surplus [Retained Earnings]- This contains ledgers like Capital
Reserve, General Reserve, Reserve for Depreciation and so on.
Current
Assets- Current
Assets record the assets that do not belong either to Bank Accounts or to
Cash-in-Hand sub-groups.
·
Bank Accounts: Current
account, savings account, short term deposit accounts and so on.
·
Cash-in hand: Tally
automatically creates Cash A/c in this group. You can open more than one cash
account, if necessary.
Note: An account
under Cash-in-hand group or Bank Accounts/Bank OCC A/c group is printed as a
separate Cash Book in the traditional Cash Book format and does not form part
of the Ledger.
Deposits
(Asset):
Deposits contain Fixed Deposits, Security Deposits or any deposit made by the
company (not received by the company, which is a liability).
Loans &
Advances (Asset):
This records all loans given by the company and advances of a non-trading
nature (example: advance against salaries) or even for purchase of Fixed
Assets. We do not recommend you to open Advances to Suppliers’ account under
this Group. For further details, please refer to the section on Common Errors.
Stock-in-hand:
This
group contains accounts like Raw Materials, Work-in-Progress and Finished
Goods. The balance control depends on whether you have selected Integrated
Account-cum-Inventory option while creating the company. (Refer to Company
creation section for more details) Let us consider these options:
Integrated
Accounts-cum-Inventory: This option has a significant effect on the
Balance Sheet and Profit & Loss Account. If set to Yes, it brings the
stock/inventory balance figures from the inventory records and provides a drill
down to the Stock registers from the Balance Sheet. You are not allowed to
directly change the closing balance of an account under this group. You are
allowed to pass transactions in Inventory records and the account balances are
automatically reflected in the Balance Sheet as Closing Stock.
Non-integrated
Accounts-cum-Inventory: If Integrated Account-cum-Inventory option is set
to No, it ignores the inventory books figures and picks up manually entered
closing stock balances from the ledger account created. This provides the
facility to maintain accounts separately and inventory separately.
You are not
allowed to pass transactions if your accounts that come under this Group. It
allows you to hold opening and closing balances only. Since no vouchers can be
passed for these accounts, they are the only accounts for which the closing
balances can be directly altered (by an authorised user only).
Sundry
Debtors:
For customer accounts refer to common and possible errors in grouping of
accounts section.
Current
Liabilities- Accounts
like Outstanding Liabilities, Statutory Liabilities and other minor liabilities
can be created directly under this group. Sub-groups under Current Liabilities
are Duties and Taxes, Provisions and Sundry Creditors
Duties and
Taxes:
Duties and Taxes contain all tax accounts like VAT, CENVAT, Excise, Sales and
other trade taxes and the total liability (or asset in case of advances paid)
and the break-up of individual items.
Provisions: Accounts like
Provision for Taxation, Provision for Depreciation and so on are recorded under
Provisions.
Sundry
Creditors:
For trade creditors, refer to common and possible errors in grouping of
accounts section.
Investments- Group your
investment accounts like Investment in Shares, Bonds, Govt. securities, long
term Bank deposit accounts and so on. This allows you to view the total
investments made by the company.
Loans (Liability)-
Loans
that a company has borrowed, typically long-terms loans.
·
Bank OD Accounts [Bank OCC Accounts]: Tally
provides you with distinct types of Bank Accounts,
·
Bank OCC A/c: To record the company’s
overdraft accounts with banks. For example, Bill Discounted A/c’s and
Hypothecation A/c’s etc.
Note: An account
under Bank OCC A/c group is printed as a separate Cash Book in the traditional
Cash Book format and does not form part of the Ledger.
·
Secured Loans: Term loans or other
long/medium term loans, which are obtained against security of some asset.
does not verify the existence of the security. Typical accounts are
Debentures, Term Loans, and so on.
·
Unsecured Loans: Loans obtained without any
security. Example: Loans from Directors/partners or outside parties.
Suspense
Account – In
modern accounting, many large corporations use a Suspense Ledger to track the
money paid or recovered, the nature of which is not yet known. The most common
example is money paid for Traveling Advance whose details will be known only
upon submission of the Travelling Allowance bill. Some companies may prefer to
open such accounts under Suspense Account.
Loans and
Advances (Asset) group: The Suspense Account is a Balance Sheet item. Any
expense account even if it has ‘suspense’ in its name, it should be opened
under Revenue group like Indirect Expenses and not under Suspense Account
group.
Miscellaneous
Expenses (Asset)- This
group is typically used for legal disclosure requirements such as Schedule VI
of the Indian Companies Act. It should hold incorporation and pre-operative
expenses. Companies would write off a permissible portion of the account every
year. A balance remains to an extent that cannot be written off in Profit &
Loss Account. Tally does not show loss, carried forward in the Profit &
Loss Account, under this group. The Profit & Loss Account balance is
displayed separately in the Balance Sheet.
Branch/Divisions-
This
maintains ledger accounts of all your company’s branches, divisions,
affiliates, sister concerns, subsidiaries and so on. Tally permits Sales and
Purchase transactions to take place with accounts opened here. Remember, these
are their accounts in your books and not their books of accounts. Just treat
them as any other party account. If you wish to maintain the books of a
branch/division on your computer, you must open a separate company. (Tally
allows maintenance of multiple company accounts).
Sales Account-
You
can classify your sales accounts based on Tax slabs or type of sales. This also
becomes a simple mechanism for preparation of Tax returns.
For example,
·
Domestic
Sales
·
Export
Sales
·
Now
under Domestic Sales open the following ledgers:
·
Sales
(10%)
·
Sales
(5%)
·
Sales
(exempt)
You can even
open an account as Sales Returns under the group Domestic Sales to view your
net sales after returns (or the returns may be directly passed through Journal
against the specific Sales account).
Note: Do not create
customer accounts under this group. For more details, refer to common and
possible errors in grouping of accounts section.
Purchase
Account- This
is similar to sales accounts, except for the type of transactions.
Direct Income
[Income Direct]- These
are Non-trade income accounts that affect Gross Profit. All trade income
accounts fall under Sales Accounts. You may also use this group for accounts
like Servicing, Contract Charges that follow sales of equipment.
For a
professional services company, you may not use Sales Account group at all.
Instead, open accounts like Professional Fees under this group.
Indirect
Income [Income Indirect]- These are miscellaneous non-sale income accounts.
Example: Rent Received and Interest Received.
Direct
Expenses [Expenses Direct]- These are Manufacturing or direct
trading expenses. These accounts determine the Gross Profit of the company.
Indirect
Expenses [Expenses Indirect]- All administrative, selling or
non-direct expenses.
Profit &
Loss Account is a reserved primary account in Tally. You can use this account
to pass adjustment entries through journal vouchers. For example, transfer of
profit or loss account to Capital or Reserve account.
Common and
Possible Errors in Grouping and Account Classification
Debtor/Creditor classification– Accounts of
parties with whom your company is trading should be opened under any of the
following groups (or sub-groups under them):
·
Sundry
Debtors
·
Sundry
Creditors
·
Branch/Divisions
Sales and
Purchase account groups are meant for revenue accounts and are reflected in the
Profit & Loss Account. If you open party accounts under these groups, it
becomes difficult to pass sales or purchase voucher transactions.
For example,
in a sales voucher transaction entry, you must debit an account, which can be
sundry debtor, branch/division or even a sundry creditor. Moreover, other
facilities like bill-wise allocation and tracking will not be available unless
the accounts belong to one of these groups.
Opening two
accounts of the same party- Tally classifies debtors, creditors
and branch/divisions for convenience. This helps you in the process of keeping
the accounts of a particular group together during display and analysis. Thus,
you can pass both sales and purchase entries for a party account placed under
Sundry Debtors. Use the classification depending on the most natural group for
the party.
For example,
parties from whom you buy frequently can be placed under Sundry Creditors, as
that is the natural place to look for their account. Tally does not restrict
the accounts from having obverse balances. Thus, a Sundry Debtor can have a
credit balance depending on the state of his account.
Therefore, you
need not open two accounts for the same party – one under Sundry Debtors and
another under Sundry Creditors. Tally restricts opening of two identical ledger
accounts. In such cases, you may decide to circumvent by marking one account as
“A & Co – S/Dr” and another “A & Co – S/Cr”. This
will allow you to have two accounts of the same party under two groups, but you
will lose the advantage of analysing net position at a single instance. It is
always better to maintain a single account to obtain best benefits.
Expenditure
items are entered under Liabilities group. For example, the expenditure item
Rates & Taxes under the group Duties and Taxes.
The group
Duties and Taxes is specifically meant to handle taxation liabilities of your
company. Rates & Taxes and other statutory expenses should be placed under
Indirect Expenses.
Simply
adhering to the reserved groups may be sufficient for many organizations. For
greater diversity, Tally allows you to create your own groups, either as
sub-groups or primary groups. Groups can be sub-classified to practically an
unlimited level, giving you a virtual accounting tree. At the lowest level, of
course, would be the ledger account.
Note: While it is
necessary to assign every ledger to a group/sub-group, it is not essential to
have your own sub-classification of accounts; you may simply use the reserved
groups for grouping your ledger accounts.
Pre-Defined
Groups- There
are twenty eight pre-defined groups in Tally. These groups are a part of the
chart of accounts for most organizations. For example, Sales Accounts is a
pre-defined group. All sales ledgers can be classified under this group.
Out of the twenty-eight
pre-defined groups, fifteen are primary groups and thirteen are sub-groups. The
user can create any number of primary groups and sub-groups.
Primary Groups | Subgroups |
Branch / Divisions | Bank Accounts |
Capital Account | Bank OD A/c |
Current Assets | Cash-in-hand |
Current Liabilities | Deposits (Asset) |
Direct Expenses | Duties & Taxes |
Direct Incomes | Loans & Advances |
Fixed Assets | Provisions |
Indirect Expenses | Reserves & |
Indirect Incomes | Secured Loans |
Investments | Stock-in-hand |
Loans (Liability) | Sundry Creditors |
Misc. Expenses | Sundry Debtors |
Purchase Accounts | Unsecured Loans |
Sales Accounts | |
Suspense A/c |
Out
of the fifteen primary groups, nine primary groups appear in the balance sheets
that are capital in nature and six primary groups appear under Profit &
Loss account which are revenue in nature.
The
sub-groups that form a part of the balance sheet are:
Pre-defined Subgroups | Under |
Bank Accounts | Current Assets |
Bank OD A/c | Loans (Liability) |
Cash-in-hand | Current Assets |
Deposits (Asset) | Current Assets |
Duties & Taxes | Current Liabilities |
Loans & Advances | Current Assets |
Provisions | Current Liabilities |
Reserves & | Capital Account |
Secured Loans | Loans (Liability) |
Stock-in-hand | Current Assets |
Sundry Creditors | Current Liabilities |
Sundry Debtors | Current Assets |
Unsecured Loans | Loans (Liability) |
Note: Primary groups cannot
be deleted.
Voucher Entry in Tally
Lesson
Objectives
On completion
of this lesson, you will be able to
·
Describe
the purpose of the Tally Accounting Vouchers
·
Create
and alter Accounting Vouchers
·
Use
vouchers to enter Accounting transactions
·
Describe
the use of Non-Accounting Vouchers
·
Describe
the purpose of the Tally Inventory vouchers
·
Create
and alter Inventory Vouchers
·
Using
vouchers to enter Inventory transactions
In accounting
terms, a voucher is a document containing the details of a financial
transaction. For example, a purchase invoice, a sales receipt, a petty cash
docket, a bank interest statement, and so on. For every such transaction made,
a voucher is used to enter the details into the ledgers to update the financial
position of the company. This feature of Tally will be used most often.
Tally follows the Golden Rule
of Accounting :
Real
Accounts
·
Debit What Comes in
·
Credit What Goes out
Personal
Accounts
·
Debit The Receiver
·
Credit The Giver
Nominal
Accounts
·
Debit
Expenses and Losses
·
Credit
Incomes and Gains
Accounting
Vouchers
Tally is
pre-programmed with a variety of accounting vouchers, each designed to perform
a different job. The standard Accounting Vouchers are:
·
Contra
Voucher (F4)
·
Payment
Voucher (F5)
·
Receipt
Voucher (F6)
·
Journal
Voucher (F7)
·
Sales
Voucher /Invoice (F8)
·
Credit
Note Voucher (CTRL+ F8)
·
Purchase
Voucher (F9)
·
Debit
Note Voucher (CTRL+ F9)
·
Reversing
Journals (F10)
·
Memo
voucher (CTRL+ F10)
·
Optional
Voucher: All the available vouchers in Tally (except non-accounting vouchers)
can be marked optional, if required.
·
Post-dated
voucher: All the available vouchers in Tally can be marked post-dated, if
required.
You can alter
these vouchers to suit your company, and also create new ones. Read ahead to
understand the function of each voucher type. The following exercises are
sample enteries for understanding Voucher entry in Tally, do not make these
entries.
Contra
Voucher (F4)
Use a Contra
Voucher to record the entry. Setup:
·
In
Voucher entry mode, press F12: Contra Configuration and set the following to
Yes:
·
Skip
the Date field in Create Mode (faster entry!)
·
Use
Cr/Dr instead of To/By during entry
·
Warn
on Negative Cash Balance
·
Show
Ledger Current Balances
·
Show
Balances as on Voucher Date
Payment
Voucher (F5)
Use a Payment
Voucher to record the entry.
Go to the
Gateway of Tally > Accounting Vouchers > F5: Payment.
Payment in
Single Entry Mode
In Voucher
entry mode, use F12: Payment Configuration and set Use Single Entry mode for
Pymt/Rcpt/Contra to Yes.
The advantage
of a single-entry mode is that you can select multiple debits or credits
depending on the type of entry. Similarly, the transactions can be recorded in
single entry mode even in Receipt and Contra vouchers.
Warn on Negative Cash Balance
Tally displays
a warning if the cash balance is NIL when Warn on Negative Cash Balance is set
to Yes in the F12: Payment Configuration. For example, a cash ledger account
has no balance. A payment of Rs. 4,500 towards Telephone expenses is to be
made. In the process of making the payment, Tally displays a warning at the
time of accepting the entry.
In addition to
the warning, Tally also displays the negative balance amount in Red.
Receipt
Voucher (F6)
Use a Receipt
Voucher to record the entry.
Ensure in F12:
Payment Configuration, Use Single Entry mode for Pymt/Rcpt/Contra is set to No.
Go to the
Gateway of Tally > Accounting Vouchers > F6: Receipt.
Journal
Voucher (F7)
Use the Journal
Voucher to adjust the two accounts.
Go to the
Gateway of Tally > Accounting Vouchers > F7: Journal.
Sales
Voucher (F8)
Use a Sales
Voucher for making this entry.
Go to the
Gateway of Tally > Accounting Vouchers > F8: Sales.
Credit
Note Voucher (Ctrl + F8)
This voucher
type is made available when the option Use Debit/Credit Note to is set to Yes
in the
F11: Features
(F1: Accounting features).
Use a Credit
note to record this entry.
Go to the
Gateway of Tally > Accounting Vouchers > F8: Credit Note.
Purchase
Voucher (F9)
A company buys
computer parts on credit.
Use a Purchase
Voucher to record this entry.
Go to the
Gateway of Tally > Accounting Vouchers > F9: Purchase.
Debit
Note Voucher (Ctrl + F9)
This voucher
type is made available when the option Use Debit/Credit Notes is set to Yes in
the
F11: Features
(F1: Accounting Features).
Use a Debit
Note to record this entry.
Go to the
Gateway of Tally > Accounting Vouchers > F9: Debit Note.
Reversing
Journal Voucher (F10)
Reversing
Journals are special journals that are automatically reversed after the date of
the journal. They exist only for a day and are effective on the date of the
reversing journal. This voucher type is available only if the feature Use
Reversing Journals & Optional Vouchers is set to Yes in the F11: Features
(F1: Accounting Features).
Memo
Voucher (Ctrl + F10)
Memo Voucher
is a non-accounting voucher and the entries made using it will not affect your
accounts. In other words, Tally does not post these entries to ledgers but
stores them in a separate Memo Register. You can alter and convert a Memo
voucher into a regular voucher when you decide to bring the entry into your
books.
Memo vouchers
are used for the following purposes:
1. Making
suspense payments-
For example, the company gives an employee cash to buy office supplies, the
exact nature and cost of which are unknown. You could have entered a voucher
stating petty cash advance, a voucher to record the actual expenditure details
when they are known, and another voucher to record the return of surplus cash.
However, a simpler way is to enter a memo voucher when the cash is advanced,
and then turn it into a Payment voucher for the actual amount spent, when
known.
2. Vouchers not
verified at the time of entry- Sometimes it so happens that you do
not understand the details of a voucher you are entering. In such cases, enter
it as a Memo voucher and amend it when you get the details.
3. Items given on
approval-
Usually, entries are made into the books only after a sales transaction is
completed. Items given on approval, can be tracked by using a Memo voucher. It
can either be converted into a proper Sales voucher or be deleted depending on
the outcome.
Optional
Voucher-
This is
another non-accounting voucher which is available only if the feature Use
Reversing Journals & Optional Vouchers is set to Yes in the F11: Features
(F1: Accounting Features). It differs from the Memo voucher in two respects:
·
It
is not a voucher type, since all the other voucher types can be marked as
Optional during a voucher entry.
·
You
have the option to bring this voucher into your accounts temporarily and see
its effect on financial reports. Any voucher type (except non-accounting
voucher) can be designated as an Optional voucher.
Post-dated
Vouchers
Post-dated
Vouchers are ignored by Tally until the date in question. This is useful for
entering transactions that take place on a regular basis. For example, if you
pay for something by instalments, you can set-up the payments in advance, and Tally
will only enter them in the ledgers as and when they fall due. A voucher is
marked as Post-dated while creating or altering it.
Creating
a New Voucher Type
National
Traders wants to record bank and petty cash payments differently and needs two
new voucher types to replace the pre-defined Payment voucher. In order to do
this:
Create a Bank
Payment voucher
Go to the
Gateway of Tally > Accounts Info. > Voucher Types > Create.
1. Name: Bank Payment
2. Type of
Voucher:
Payment (Specify the default Tally voucher, whose functions the new voucher
should copy).
3. Abbr.: Bank Pymt
(Specify the abbreviation to denote this new voucher in reports)
4. Method of
Voucher
Numbering: Automatic
You can
choose one of the following methods for numbering from the pop-up:
Automatic For Tally to do it for you.
Manual You do it. You can also specify if you
wish to prevent duplicates.
None To disable numbering for this
voucher type.
5. Use Advance
Configuration:
No
6. Use EFFECTIVE
Dates for Vouchers:
No
7. Make
‘Optional’ as default: No (This is to set the voucher type as an Optional
voucher, by default)
8. Use Common
Narration: Yes
9. Narrations for
each entry: No
10. Print after
saving Voucher:
No
11. Name of Class: Skip.
Displaying
and Altering a Voucher Type
Observe the
menu, you will notice that you can also display and alter voucher types.
Selecting these options brings up a List of Voucher Types, from which you can
select the one you want to view or work on. Apart from the heading, the Voucher
Type Display/Alter screens are identical to the Creation screen.
Inventory
Vouchers
Tally
inventory vouchers perform the same function in the inventory system as
accounting vouchers do. They are the means by which you enter transactions
relating to the Inventory. The vouchers record transactions relating to the
issue and receipt of stock, the transfer of stock between godowns, and physical
stock adjustments. The following inventory vouchers are available in Tally:
·
Purchase
Order (Alt+F4)
·
Sales
Order (Alt+F5)
·
Rejections
Out (Alt+F6)
·
Rejections
In (Ctrl+ F6)
·
Stock
Journal (Alt+F7)
·
Delivery
Note (Alt+F8)
·
Receipt
Note (Alt+F9)
·
Physical
Stock (Alt+F10)
Purchase Order
A Purchase
order entry has to be made in the books of the company to assist them in checking
whether the goods have been received or not. The Purchase Order number can be
used as a reference.
For example,
the company wishes to place an order with the supplier for some goods.
Purchase Order
Description- Records placing an order for stock
items to suppliers.
Details recorded– Supplier’s Ledger account, Name and address,
Order details, name of stock item, Due on, Godown, Quantity, Rate, Amount,
Narration.
Sales
Order
A Sales Order
entry has to be made to record this. The Sales Order number can be used as a
reference. For example, a customer places an order with the company for
purchasing some goods.
Sales Order
Description- Records order details for stock
items received from customers.
Details recorded- Customer’s Ledger account, Name and address,
Order details, name of stock item, Due on, Godown, Quantity, Rate, Amount,
Narration.
Rejections
Out
A Rejections
Out entry is passed to record the rejected goods. This is a pure inventory
voucher. For example: We have purchased some goods and have rejected a part of
it.
Rejections Out (Purchase
Returns)
Description+ Records rejected stock details
returned to suppliers.
Details recorded– Ledger Account, Suppliers name and address,
stock item, Tracking details, Order details, Godown, Quantity, Rate, Amount,
Narration.
Rejections
In
A Rejections
In entry is passed to record the rejected goods. The Rejections In entry is a
pure inventory voucher. For example a customer has rejected goods that was sold
earlier.
Rejections In (Sales Returns)
Description- Records rejected stock details
received from customers
Details recorded- Ledger account, Customer’s name and address,
stock item, tracking details, order details, Godown, Quantity, Rate, Amount,
Narration.
Stock
Journal
To record the
consumption of goods there is no need for entries on both sides of the voucher.
Such entries can be entered in a stock journal voucher. For example: the
company transfers items of stock from the warehouse to the shop.
Stock Journal
Description+ Essentially records the transfer of
stock from one Godown to another.
Details recorded- Names of from and to godowns, name of stock
item, quantity, rate, amount, narration.
Delivery
Note
Goods that are
being delivered to a customer are recorded in a Delivery Note voucher.
Delivery Note
Description- Records delivery of new stock to
customers
Details recorded– Reference, ledger account, supplier’s (if
supplementary details are set to yes in F12: Delivery Note Configuration) then,
name and address, Order & dispatch details, name of stock item, Tracking
details, Order details, Godown, Quantity, Rate(optional), Amount(optional),
narration.
Receipt
Note
Goods that are
received from the supplier are recorded in a Receipt Note (Goods Receipt Note –
GRN) voucher.
Receipt Note
Description– Records receipt of new stock from
suppliers
Details recorded– Reference, ledger account, (If
supplementary details are set to yes in F12: Receipt Note Configuration) then,
Order details, Supplier’s name and address, name of stock item, Tracking
details, Order details, Godown, Quantity, Rate (optional), Amount (optional),
narration.
Physical
Stock Voucher
Tally
considers the stock available based on the entry made in a physical stock
voucher. For example, on conducting a stock-check, the company finds a
discrepancy between the actual stock and the recorded stock figure.
Physical Stock Voucher
Description+ Records the physical stock count as
the new stock balance
Details recorded– Name of stock item, Godown, Physical stock
quantity.
Pure
Inventory Transactions
Pure inventory
Transactions (vouchers) are those that do not affect financial records. They
affect only the stocks. There will be a rise or fall in the stock when such
vouchers are entered.
The different
pure inventory vouchers are:
·
Rejections
Out (Alt+F6)
·
Rejections
In (Ctrl+F6)
·
Stock
Journal (Alt+F7)
·
Delivery
Note (Alt+F8)
·
Receipt
Note (Alt+F9)
·
Physical
Stock (Alt+F10)
Setup:
·
To
enable Delivery Note and Receipt Note, set Yes to Use Tracking Numbers and Use Rejection
Notes in F11: Features (F2: Inventory Features).
·
Go
to the Gateway of Tally > F12: Configuration > Invoice/Orders Entry – Set
Com- plete Accounting Allocations in Order/Delivery Note to Yes.
·
Make
sure that Inventory Values are affected? is set to Yes in all ledger accounts
under the groups Sales Accounts and Purchase Accounts.
An entry made
in a purchase voucher can update the stocks. It is not necessary to make a
separate entry in a Goods Receipt Note. This holds true for the goods delivered
and recorded in the Sales Voucher itself.
We shall now
learn how to enter pure inventory vouchers.
Invoicing
Tally has an
in-built system to create and print sales invoices. You will now record sales
and purchase invoice details, adjust accounting and inventory balances.
To enable the
option of invoicing, set Yes to Allow Invoicing, Enter Purchases in Invoice
Format and Separate Discount Column in invoices in F11: Features (Accounting
Features/ Inventory Features).
·
Ensure
that the Inventory values are affected? is set to Yes in Purchases Ledger.
·
Ensure
that the Inventory values are affected? is set to Yes in Parts Sales, Software
Sales and Computer Sales.
Make the
following entry of Sales in Voucher Mode.
Go to the
Gateway of Tally > Accounting Vouchers > F8: Sales.
·
Ensure
the button above the Post-Dated option reads As Invoice. This button enables
you to toggle between the voucher and invoice format for data entry. The button
visible is the format NOT in use.
·
Enter
the following data as on 1-7-2009 to record the sale of 2 Nos of USB Pen Drives
64 MB to Supreme Computers. (at the standard price) and update the accounting
and stock records:
Item
Invoice and Account Invoice
Tally gives
you an option called Account Invoice where you can select the ledgers instead
of the stock items. An Item Invoice on the other hand, allows you to select
stock items instead of ledgers.
Businesses
that require an invoice raised with the item details, can select the Item
Invoice option. Businesses that want to raise invoices for services rendered,
can do so by selecting the Account Invoice.
At this point,
it is understood that you already know how to enter an Item Invoice, by
selecting items and entering their quantity, rate, discount, etc.
Walk-through
to create an Item Invoice
1. Ensure that
you are at the Gateway of Tally of Indus Enterprises.
2. Ensure Allow
Invoicing option in F11: Features (F1: Acounting Features) is set to Yes.
3. Go to the
Gateway of Tally > Accounting Vouchers > F8: Sales.
4. The invoice
screen must display the columns – Name of Item, Quantity, Rate, per, Amount,
etc.
5. Party’s A/c
Name: Customer One (create one, if it is not displayed in the list of ledgers).
6. Press Enter
till you reach the ‘Name of Item’ field and press the spacebar to view the List
of Stock Items.
7. The different
stock items with their balances are displayed.
Walk-through
to create an Account Invoice
Go to the
Gateway of Tally > Accounting Vouchers > F8: Sales.
1. The invoice
screen must display the following columns: Name of Item, Quantity, Rate, per
and Amount.
2. Click on the
Acct Invoice button. You will notice that Tally now displays the columns as
3. Particulars,
Rate, per and Amount.
4. Select the
Party’s A/c Name as Customer One.
5. Press Enter
till you reach the Particulars field. Press the Space Bar and Tally displays
the List of Ledgers.
6. Select the
Consulting Fees (create one if it is not displayed under Direct Income).
7. Specify the
amount as Rs. xxxxx and press Enter.
Shortcut
Keys
List of Function Keys
Function Key | |||
Sl. No | Key | Functionality | Availability |
1. | F2 | To change the menu | At |
2. | F4 | To select the contra | At |
To | At | ||
To | At | ||
To | At | ||
To | At the bill receivable and payable | ||
To | At | ||
To | At | ||
3. | F5 | To select the payment | At |
To switch between grouped and ledger | At | ||
To reconcile | At | ||
4. | F6 | To | At |
To | At the bill receivable and payable |
5. | F7 | To | At accounting creation and |
| ||||
To | At |
| ||||||
To | At the group summary | and | group |
| ||||
6. | F8 | To | At |
| ||||
7. | F9 | To | At |
| ||||
8. | F10 | Navigate between accounting | At |
| ||||
9. | F11 | To | At |
| ||||
10. | F12 | To | At |
| ||||
|
|
|
|
| ||||
Special Function Key
| ||||||||
Sl. No | Key | Functionality | Availability | |||||
1. | Alt | To | At | |||||
To | At | |||||||
To | At almost all screens in | |||||||
2. | Alt+ | To | At almost all screens in | |||||
3. | Alt | To select the company info menu. | At | |||||
To | ||||||||
4. | Alt | To | At | |||||
5. | Alt | To | At | |||||
6. | Alt | To | At |
To | At | ||
7. | Alt | To add multiple columns to a | At |
8. | Alt | To | At |
9. | Alt | To | At |
10. | Ctrl | To | At |
11. | Ctrl+ | To | At |
12. | Ctrl | To | At |
13. | Ctrl | To | At |
14. | Alt | Recalls | At creation/alteration of voucher |
15. | Ctrl | Recalls | At creation/alteration of voucher |
16. | Alt | To | At Voucher and Master (Single) |
17. | Alt | To cancel a voucher in Day | At |
18. | Alt | To | At |
19. | Alt | To | At | ||
20. | Alt | To | At | ||
21. | Alt | To | At | ||
22. | Alt | To | At | ||
23. | Ctrl | To retrieve all lines which are | At | ||
Key Combination Used For Navigation |
| ||||
Sl. No | Key | Functionality | Availability |
| |
1. | Enter | To accept anything you type | You |
| |
To accept |
| ||||
To |
| ||||
2. | Esc | To | At almost all screens in Tally. |
| |
To |
| ||||
To |
| ||||
3. | Shift + Enter | To view next level details and | At |
| |
4. | Space | Select | At |
| |
5. | Ctrl + Space | Select | At |
| |
DTP
Desktop Publishing
DTP, the
abbreviation for Desktop Publishing, is one of the most important components of
localization. DTP in general refers to make text editing, layout, graphic and
image processing by computer system and complete the typeset in line with
publishing requirement. Desktop Publishing is a publishing software used to
create high quality printed material for individuals, businesses and
organizations. The DTP software provides a good control over design and layout
of a page as compared to the word processor.
Types- DTP can be
two types:
1. Creates
electronic pages
2. Creates
virtual pages
The virtual
pages are printed on physical papers such as magazines, books, newspaper etc.
Usage- Desktop
publishing (DTP) is used to publish magazines, books, newspapers, comics etc.
Advantages- Desktop
publishing (DTP) refers to the use of a digital desktop for laying out and
constructing documents. The term is sometimes used to refer to processes that
allow printing out paper copies of documents in a localized hardware scenario.
It may also refer simply to the creation and construction of digital documents
on a desktop.
Desktop
publishing is also known as computer-aided publishing.
Popular
desktop publishing software’s- Adobe FrameMaker, Adobe PageMaker,
Adobe InDesign, Microsoft Office Publisher
Corel Ventura,
Express Publisher, Ventura Publisher, etc.
CorelDRAW
CorelDraw is
an enormously powerful graphic design package. It is different from bitmap
graphic design package, and is a vector-based program. It creates and handles
images as mathematically defined vectors. Vectors are objects with magnitude
and direction. You can define smooth curves in CorelDraw. It will retain the
smoothness when they are enlarged, but this is not the same with bitmap
graphics. Bitmap graphic images become grainy when they are enlarged. CorelDraw
images are great for printed output.
CorelDraw
images can be exported as “gif or jpeg” for the web page. A complete CorelDraw
page can also be saved for the World Wide Web. The tools and other special
features of CorelDraw help us to design stunning vector graphics.
HOW TO WORK IN
COREL DRAW
To open
CorelDraw
Step 1: Click on Start
Step 2: Select Programs
Step 3: CorelDraw
Step4: Click on CorelDraw
Select New Graphic for creating a new
CorelDraw image. About the other options:
Open last edited: will open
the last created/modified CorelDraw file
Open Graphic: It gives you the
option to browse and open the desired file.
Template: It provides
ready to use templates for designing.
Corel Tutor: Provides
tutorials on CorelDraw.
What’s new: Provides the
new features of this version over the previous version.
On Selecting and clicking on New
Graphic you get the following screen:
The above
screen contains:
Title Bar: It shows the
File name
Menu Bar: In contains
all the menus
Standard tool bar: It contains
some of the standard icons (open, save, new etc.)
Property Bar: It shows the
property of the selected object ( height, width, page size, page type, etc)
Rulers: It is used to
determine the size of the page and size & position of the object.
Page Tab: It shows the
number of pages and the current page you are working on.
Navigator: It is used
for navigating between pages.
Status Bar: It provides
information about the currently selected object or the action.
Tool Box
Tool Box: It contains
all the tools.
Color Pallet: It contains
the colors.
Drawing Window: This is the
area used for drawing objects. It also contains the drawing page.
Drawing Page: This is the
place where you can draw the object. When you give the print command it only
prints those objects which are there in the drawing page.
Tools
Pick Tool: It is used
for selecting an object. With the help of this we can resize the object. If an
object selected and you click again on it, the points in the corners change to
circular arrows, which help in rotating the object.
·
Selection
for rotation
·
Normal
Selection
Shape Tool: With the help
of this tool you can reshape any object by selecting the node and by
dragging/changing the position of the node.
Knife Tool: It is used
for cutting the object into two parts.
Erase Tool: It helps to
erase the object.
Free Transform Tool: Used for
giving free rotation to the object. With this we can take any point as the
center point of the object.
Zoom Tool: Used for
zooming the object.
Pan Tool: Used for
panning / scrolling up-down, left-right when we have zoomed the file
Freehand Tool: It is used
for drawing object freely.
Bezier Tool: It also
creates shapes, but by clicking in one point for making it the first point,
then click for 2nd point and 3rd point and so on until you want. But you have
to join the last point with the first point.
Artistic Media Tool: With this you
can draw some objects. It has Brush, Sprayer, Calligraphic and Pressure options
for designing.
Dimension Tool: It gives you
the exact height and width of the object.
Connector Line Tool: Used for
creating lines.
Interactive Connector Tool: It also
creates lines.
Rectangle Tool: Used for
drawing a rectangle. You can also have a rounded cornered rectangle. Press and
hold CTRL and draw to make a square.
Ellipse Tool: Used to
create circles. Press and hold CTRL and draw to make a perfect circle.
Polygon Tool: Used for
creating polygonal shapes (star, 5-sides/6-sides objects etc.). You will have
to define the number of sides for the polygon.
Spiral Tool: Used for
creating a spiral / net.
Graph Paper Tool: Provides a
graph paper structure. With the help of this you can make exact figures.
Text Tool: Helps to
write Paragraph or Artistic text. The text can be written on a defined path,
around any object. Also you can convert the text to curves for giving a new
shape to the text.
Interactive Fill Tool: Used for
filling up the object as well as filling the outline of the object in any
color.
Interactive Mesh Tool: Used for
modifying, giving a new look (shape) to the object.
Interactive Transparency Tool: Used for
providing transparency effect to the object.
Interactive Blend Tool: A special
effect that is created by blending one object with another through a
progression of shapes and colors. You can also provide a path for blending.
Interactive Contour Tool: Used for
giving a special effect by adding evenly spaced concentric lines inside or
outside the borders of an object. These lines use the same shape as the outline
of the original object, but they are smaller or larger depending on where they
are created.
Interactive Distortion Tool: You can push
or pull the nodes of objects you’re distorting away from or towards their
centers.
Interactive Envelop Tool: A feature
that allows you to distort the shape of an object. Distortion is created by
dragging nodes on an imaginary box (the envelope) which in turn distorts the
object.
Interactive Extrude Tool: A feature
that lets you give objects a three-dimensional (3D) look by creating the
illusion of depth. You can change the direction and depth of the extrude, the
position of the vanishing point, its placement in 3D space, and its color.
Interactive Drop Shadow Tool: With the help
of this tool, you create the illusion of depth between objects. You can add
drop shadows to almost all objects, except link groups such as blended objects,
contoured objects, beveled objects, extruded objects, or other drop shadows.
Eyedropper Tool: Used for picking up a
color.
Paint Bucket Tool: Used for
removing the fill / outline color to provide transparent effect to the object.
Outline Tool: Helps to give
outline to the object. You can set the outline color and the thickness of the
outline. Also you can set no outline of the object.
Fill Color Option: It helps to
fill a solid color to the object.
·
Fountain Fill Option: Fountain fill
is also known as a gradient fill. It is a progression of colors through the
Color Wheel that follows a linear, radial, conical, or square path.
·
Pattern Fill Option: Pattern fills
are preset, symmetrical images that can be tiled. You can import bitmaps or
vector graphics for use as pattern fills, or you can create simple two-color
bitmap patterns. There are three types of pattern fills: two-color, full-color,
and bitmap.
·
Texture Fill Option: A fractally
generated fill, such as water, minerals, and clouds that you can use to give
your objects a natural appearance.
·
PostScript Fill Option: A PostScript
texture is a texture fill designed using PostScript language. Some textures are
very complex, and large objects that contain PostScript texture fills may take
time to print or to update on screen.
·
No Fill option: The object is
filled with, no color/texture/pattern etc.
Node
Editing
Node: The Square
points at the end of lines and curve segments. You can change the shape of a
line or curve by dragging one or more of its nodes
When you
select any point of the object with SHAPE tool, which is drawn using freehand
tool / Bezier tool / artistic media tool, you will get the property bar for
editing the nodes of that object. In the property bar you will find many
options. These options are used for:
+ sign: Adds a
point/node in between two nodes.
– sign: Deletes the
selected node/nodes.
Join two nodes: It joins two
nodes (selected). It works with unclosed path.
Break Curve: It breaks the
curve. When a node is selected and we click on this option, the closed curve is
broken.
Convert curve to line: It converts
the curve/circular path to a straight line.
Convert line to curve: It converts a
straight line to curve.
Make node Cusp: The control
points of a cusp node move independently from one another. A curve that passes
through a cusp node can bend at a sharp angle.
Make node Smooth: The control
points of a smooth node are always directly opposite each other. When you move
one control point, the other moves also. The control points of a smooth node
may be of different lengths. Smooth nodes produce a smooth transition between
line segments.
Make node Symmetrical: The control
points of a symmetrical node are always directly opposite each other. Also, the
control points are always equal lengths. Symmetrical nodes produce the same
curvature on both sides of the node.
Reverse curve direction: It reverses
the direction of the curve.
Extend curves to close: It helps to
close a curve. Select the 1st and the last node and click on this option, it
will join the two nodes to give a closed curve.
Extract sub path: You can create
a sub path from any object.
Auto-close curve: It also
closes the curve, but in this case you select either 1st node or the last node,
and when you click on this option it closes the curve.
Stretch and scale nodes: It helps to
scale a particular node (selected) not the whole object.
Rotate and skew nodes: It helps to
rotate or skew a particular node (selected) not the whole object.
Align nodes: It helps to
align the selected nodes and their control points either horizontally or
vertically.
Elastic Mode: It makes the
node elastic, so that you can work easily.
Curve smoothness: You opts you
to enter a number for the smoothness of the curve.
Shaping
Objects
Shaping /
combining / joining objects using;
Weld: Welding
several objects binds them together to create one object with a single outline.
This new object uses the welded objects’ perimeter as its outline, and all
intersecting lines disappear. To weld objects, do the following steps:
1. Select the
object using the Pick tool.
2. Click Arrange
> Shaping > Weld
3. Click and
select the Source object check box, if you want to keep a copy of the source object after welding.
4. Click and
select the Target object check box, if you want to keep a copy of the target
object after welding.
5. Click on Weld
to
6. Click on the
object you want to be the target object for welding.
Trim: When you trim
an object, you remove the areas that are overlapped by other selected objects.
These areas are cut away, creating an entirely new shape. Trimming is a quick
way to create objects with irregular shapes. To trim objects do the following
steps:
1. Select the
object using the Pick tool.
2. Click Arrange
> Shaping > Trim
3. Click and
select the Source object check box, if you want to keep a copy of the source
object after trimming.
4. Click and
select the Target object check box, if you want to keep a copy of the target
object after trimming.
5. Click on Trim
6. Click on the
object you want to be the target object for trimming.
Intersect: Intersecting
creates a new object from the area where two or more objects overlap. The shape
of this new object can be simple or complex, depending on the shapes you
intersect. To weld objects, do the following steps:
1. Select the
object using the Pick tool.
2. Click Arrange
> Shaping > Intersect
3. Click and
select the Source object check box, if you want to keep a copy of the source
object after intersecting.
4. Click and
select the Target object check box, if you want to keep a copy of the target
object after intersecting.
5. Click on
Intersect with.
6. Click on the
object you want to be the target object for intersecting.
Transformation
Position: Lets you
position an object precisely using the Transformation Property Bar.
1. Select the
Object by Pick tool.
2. Click on
Arrange > Transformation
3. Select
Position
4. Specify the
Horizontal (H) and Vertical (V) position
5. Enable the
Relative Position check box and also select the center point.
6. Click on Apply
(if you want to change the position of the original image) Or Click on Apply to
duplicate (if you want to create a duplicate in the position specified with the
original image)
Rotation: Lets you
rotate an object around a fixed point, called the center of rotation.
1. Select the
Object by Pick tool.
2. Click on
Arrange > Transformation
3. Select
Rotation
4. Provide the
Angle/degree of rotation
5. Select the center
point for H(horizontal) and V(Vertical)
6. Enable the
Relative Centre check box and also select the center point.
7. Click on Apply
(if you want to rotate the original image) Or Click on Apply to duplicate (if
you want to create a duplicate of the original image in the angle specified by
you)
Scale and Mirror: Lets you scale
an object, or mirror an object vertically or horizontally.
1. Select the
Object by Pick tool.
2. Click on
Arrange > Transformation
3. Select Scale
& Mirror
4. Provide H
(horizontal) % of Scaling and Click on the mirror button (if horizontal mirror
is required)
5. Provide V
(vertical) % of Scaling and Click on the mirror button (if vertical mirror is
required)
6. Enable the
Non-proportional check box and also select the center point.
7. Click on Apply
(if you want to change the original image) Or Click on Apply to duplicate (if
you want to create a mirror image of the original image
Size: Lets you
resize an object by scaling it along the horizontal and vertical axis
simultaneously relative to its anchor point.
1. Select the
Object by Pick tool.
2. Click on
Arrange > Transformation
3. Select Size
4. Provide the H
(horizontal) and V (vertical) size required in inches.
5. Enable the
Non-proportional check box and also select the center point.
6. Click on Apply
(if you want to resize the original image) Or Click on Apply to duplicate (if
you want to create a duplicate of the original image in the size specified by
you)
Skew: Lets you Skew
/ Slant the horizontal and vertical lines of an object simultaneously, relative
to the object’s anchor point.
1. Select the
Object by Pick tool.
2. Click on
Arrange > Transformation
3. Select Skew
4. Provide the H
(horizontal) and V (vertical) degree, as per requirement.
5. Enable the Use
Anchor Point check box and also select the center point.
6. Click on Apply
(if you want to skew the original image) Or Click on Apply to duplicate (if you
want to create a duplicate of the original image which is skewed as specified
by you)
Align
And Distribute the Objects
To Align the Objects, do the following
steps:
1. Select the
objects by pick tool.
2. Click on
Arrange > Align and distribute.
3. Choose Align.
4. Select the
type of alignment (Left, Center, Right or Top, Center, Bottom).
5. Select and
enable the check box of “Edge of Page” or “Center of Page” Or Enable the check
box of “Align to Grid”
6. Click on
preview to check whether the result is ok. If this is what you require then
click on OK else click on Reset and do Step 4 & 5 again.
To Distribute the objects, do the
following steps:
1. Select the
objects by pick tool.
2. Click on
Arrange > Align and distribute.
3. Choose
Distribute.
4. Select the
type of distribution (Left, Center, Spacing, Right or Top, Center, Spacing, Bottom).
5. Select and
enable the check box of “Extent of Selection” or “Extent of Page” for
distribution.
6. Click on
preview to check whether the result is ok. If this is what you require then
click on OK else click on Reset and do Step 4 & 5 again.
Text
Designing
You can write
your text in a predefined path or around any object. For writing your text in a
predefined path do the following steps:
Write the
text.
Draw the Path using the freehand tool.
1. Select the
text by pick tool.
2. Click on Text
> Fit text to path. (The cursor will change to a thick arrow cursor)
3. Click on the
path drawn by you. (The text will be attached to the path)
To detach or separate the text from
the path, do the following:
1. Select the
joined text & path by pick tool.
2. Click on
Arrange > Separate
3. Select the
path by pick tool and delete it. Now you have the result. (as given right)
To write your text around any
object/shape, do the following:
1. Create the
object by freehand, Bezier, Artistic media, Rectangle, Ellipse, Polygon, Spiral
toll etc.
2. Click on Text
> Fit text to path.
3. Write your
text. The text will be written around the shape / object.
To detach or separate the text from
the shape/object, do the following:
1. Select the
joined text & object/shape by pick tool.
2. Click on
Arrange > Separate
3. Select the
shape/object by pick tool and delete it. Now you have the result.
Arrange
Menu
Apart from the options which you have
done earlier you, the other options available under arrange menu, are as
follows:
·
Group: To group a
set of objects.
·
Ungroup: To ungroup
the grouped object (selected one)
·
Ungroup all: Ungroup all
the grouped objects.
Order: Under order
we have;
·
To front: Brings the
selected object to the front of all the objects.
·
To back: Puts the
object behind all objects.
·
Forward one: Brings the
object one step forward.
·
Back one: Puts the
object one step behind.
·
In front of: On selecting
this you have to select the target object, in front of which the source object
will come.
·
Behind: On selecting
this you have to select the target object, behind which the source object will
come.
·
Reverse order: It will
reverse the order of the objects.
·
Combine: Combines to
objects.
·
Break apart: Breaks apart
the combined objects.
PHOTOSHOP
Adobe
Photoshop
– the imaging software application – has become more than an integral part of
graphic designers’ working tools. Photoshop has earned the reputation of being
a mysterious, magical environment where reality is twisted and reshaped, where
disintegrating family photos are returned to perfect condition, and where the
line between illustration and photography is freely crossed.
Photoshop
provides you some special features like, Image retouching, Advanced Imaging,
Special effect using filters, creating stunning backgrounds, images, texts and
buttons for your web pages. This is best software application available in the
market for Image Manipulation.
Work In
Photoshop
Open Photoshop
1. Click on START
2. Select
Programs
3. Select Adobe
4. Select Photoshop
5. Click on Photoshop
After finishing doing this you will
get a screen, the screen provides you the tool bar and few other windows, but
not the work area.
For work area;
1. Click on FILE
2. Click on NEW
The next screen will appear, which
will require few inputs from you, like
1. The height and
width of the work area in pixel / inches / cm / points / picas / columns,
2. The resolution
for the file
3. The image
color mode Bitmap / Grayscale / RGB / CMYK / lab color
4. The last
option for the type of background required white / background color /
transparent.
5. Give a file
name under “Name”
6. Click on OK
The normal size for work area is 640
pixels (width) x 480 pixels (height) with the resolution 72 pixels/inch.
Now as you have got the work area, you
can start working on it.
With the help of the Photoshop tool
bar you can create, edit, retouch, manipulate your drawing or imported image.
To Save Your Work
1. Click on File
2. Click on Save
/ Save as
3. Select the
directory under which the file you want to save
4. Provide a name
(if not provided at the time of creating a new file)
5. Click on Save
Note: Photoshop
saves the file in .psd file format
For saving your work either in .jpg or
in .gif for your webpage do the following;
For JPEG file format:
1. Click on File
2. Click on Save
a copy…
3. Select the
directory under which the file you want to save
4. Provide a name
5. Select JPEG
from under the “Save as” option.
6. Click on Save
For GIF file format:
1. Click on File
2. Click on
Export
3. Click on GIF89a
export
4. Without
changing anything (as above) Click on OK
5. Select the
directory under which the file you want to save
6. Provide a name
7. Click on Save
Tools
Available In Photoshop
For selection
we have Marquee, Lasso and Magic wand tool.
Under Marquee tool we have
Rectangular Marquee, Elliptical Marquee, Single row, Single column and Crop
tools. Rectangle and circular selections are possible with rectangular and
elliptical marquee respectively. If we want to select a row or a column then we
do it with single row and single column options respectively. Crop is used for
cropping. Cropping keeps the wanted area and removes the un-wanted area of the
image (means, if we want a portion of the image created by us, then we select
that area and press ENTER). This not only deletes the other portion but also
reduces the size of the file.
Under Lasso tool we have
Lasso, Polygonal Lasso and Magnetic Lasso options. Lasso tool is used for free
hand selection. In Polygonal lasso option we first click on any portion of the
object to make it the start point of selection, then we click on different
places as per the requirement, finally we click on the start point again to
close the selection. In case of magnetic lasso option, we just drag around the
object and it selects the area as per the color value.
Magic wand tool selects as
per the tolerance set by the user. The more the tolerance the more area
selected and the less the tolerance it selects lesser area. Tolerance is the
strength and the value of color (RGB/CMYK).
Move tool is used for
moving a selection or the object inside a layer. With the link option of layer
activated, it moves those layers which are linked together.
For Drawing we have Brush tool, Air Brush
tool, Pencil tool and Line tool. With the help of these tools, we can draw or
create a design/drawing etc.
Options available with these tools are
as follows:
Brush tool:
·
Opacity: It provides the strength of the color
(lightness or dark).
·
Fade __ steps: It fades the color after the
provided numbers of steps.
·
Fade to: Fades to either Transparent or to
background color.
·
Wet edges: Gives a faded effect of the color.
Air Brush tool:
·
Pressure: Same as opacity of brush tool
·
Fade __ steps: Same as brush tool
·
Fade to: Same as brush tool
Pencil tool:
·
Opacity: Same as brush tool
·
Fade __ steps: Same as brush tool
·
Fade to: Same as brush tool
·
Auto erase: Erase the
Line tool:
·
Opacity: Same as brush tool
·
Weight __ pixel: The line
thickness as defined
·
Anti-aliased: For a smooth line (not
pixilated)
·
Arrow head: (a) Start: Arrow head in the start
(b) End: Arrow head in the end
Rubber Stamp tool: Used for
copying an image and pasting in a different file or layer without using
copy-paste command.
Pattern Stamp tool: It also works same
as rubber stamp, but, first we have to define a pattern. To define pattern do
the following steps: Select the image to be used as pattern, Edit -> Define
Pattern
Eraser tool: Used for
erasing purpose.
Text tool: Used for writing text. We
can write the text in both horizontally and vertically.
Measure tool: Used to
measure the height of the object.
Paint bucket tool: Used for
filling the selection.
Eyedropper tool: Used for
picking up a color from an object, to be filled in some other object.
Zoom tool: Used for
zooming.
Hand tool: Used for scrolling up-down,
left-right when we have zoomed the file.
Gradient tool: Used for
filling a selection in multi color. The types of gradient tools are
1. Linear: Files from
top-to-bottom, left-to-right.
2. Radial: Files in a
circle.
3. Angular: Files in an
angle from one point.
4. Reflected: Files in like
linear option.
5. Diamond: Files in a
shape of diamond.
Pen tool: It is used for
drawing object in a path. These paths can be modified by the other options
available with the pen option. When any shape is made using the pen option a
work path is created under Path. Each shape is to be saved in a path, for
which, you have to create path for every shape, as you create new layers.
Options available on pen tool are:
1. Pen: The path is
drawn by clicking in different points and joining the 1st and the last point.
2. Magnetic: Draws a path
around any object. Works as a magnet while drawing the path around the object.
3. Freeform: Editable
paths are drawn in free form.
4. Add Point: For adding a
point to the path.
5. Delete point: For deleting
a point from the path.
6. Selection
tool: For
selecting the path.
7. Convert point:
Used
for giving curves to the path.
Smudge, Blur, Sharpen, Dodge, Burn,
Sponge tools are used for giving some special effect / final touching to your
image/object.
The other options available in the
tool bar of Photoshop are:
·
Background
color & Foreground color,
·
Standard
mode & Quick Mask mode,
·
Standard,
Full screen mode with menu bar & Full screen mode.
Effects
For giving
shadow, glow, bevel & emboss effects to the object in a layer, we do the
following:
Shadow: Shadow is of
two types i) Drop shadow & ii) Inner shadow. Drop shadow is used for
providing a shadow of the object which will appear below the object, and in
Inner shadow, the shadow appears inside the object.
1. Select the
object/shape
2. Click on Layer
3. Click on
effects
4. Choose drop
shadow or inner shadow (as per requirement)
In the next screen do the following:
1. Select the
Mode
2. Select the
color of shadow
3. Adjust the
opacity of shadow
4. Adjust the
angle of the shadow (where to be shown / which side of the object)
5. Adjust the
blur value (more blur > shadow lighter, less blur > shadow darker)
6. Adjust the
intensity of the color (more > darker, less > lighter)
Glow: Glow is also
of two types i) Outer glow & ii) Inner glow. Outer glow gives a glow effect
outside the object, where as inner glow gives a effect inside the object. Inner
glow is either from the center or from the edge of the object.
1. Do step 1-3 as
of shadow.
2. Choose outer
glow or inner glow (as per requirement).
In the next screen do the following:
1. Select the
mode
2. Select the
glow color
3. Select the
opacity of glow
4. Select the
blur value (more blur > more glow)
5. Select the
intensity of glow (more > more area / border)
Bevel & Emboss: Bevel is of
two types i) Outer bevel & ii) Inner bevel. Emboss is also of two types i)
Simple emboss & ii) Pillow emboss
1. Do steps 1-3
of shadow
2. Select Bevel
& emboss
Do the following in the next screen:
1. Choose the
highlight mode (opacity)
2. Choose the
shadow mode (opacity)
3. Select the
style (outer bevel or inner bevel / emboss or pillow emboss)
4. Define the
angle
5. Define the
depth (up / down)
6. Adjust the
blur value.
Different
Windows
Different
windows available in Photoshop are: Layer, Channels, Path, History, Action,
Brush, Color, Swatches, Navigator, Info and Options.
The options available
in these windows and how they work are given below.
Layer: It is always
advisable to work in layers, when creating any complex image/object. When we
erase some portion of the image, then the things which are behind that part
gets erased if not using layers, but if we are using layers, this does not
happen, as the erased part was in a different layer and the other parts are in
different layers. One can create a maximum of 99 layers in one file.
Options available in layer are:
1. Opacity: To adjust the
visibility / transparency of the layer
2. Preserve
transparency:
Preserves the transparency of the layer.
3. Layer no.: Shows the no.
of layers created with background.
4. Add mask
layer:
Makes the layer work in mask mode.
5. New: For creating
a new layer
6. Delete: For deleting
the selected layer.
7. Eye: For toggling
the visibility on/off of the layer.
8. Brush: Is seen on
the left-hand side of the selected layer, which indicates modification can be
done in this layer.
9. Link: Is used to
link other layers with the selected layer for modification.
Channels: It shows the
color channels we are working. RGB, R, G & B, if we are working on RGB
color mode.
Path: It is used
with the pen option. We can modify a path which is been created using this
option. No path can be made with the drawing tools (brush, air brush, pencil,
line).
Options available in path are:
1. Fill with
foreground color: Fills
the selected path with the foreground color.
2. Stroke with
foreground color: Strokes the selected path with foreground color.
3. Load as
selection:
Selects the current path.
4. Make work path
from selection: With
this option we can create a path from any thing and of any shape, which is been
selected. (Gets activated after any selection)
5. New: To create a
new path.
6. Delete: To delete the
selected path.
History: It shows the
history of our work, step by step.
Action:
Brush: It shows the
different shapes and sizes of the brushes available.
Color: It shows the
color depending upon the RGB settings.
Swatches: It shows the
color palette.
Navigator: It shows the
whole work area in a thumbnail.
Info: It provides
the information of RGB & CMYK color value, X-axis & Y-axis position and
the Height & Width of the object.
Option: It provides
different option available under the selected tool.
Different
Menus
In Photoshop
the file menu provides you option for creating a new file, opening an existing
file, saving a file, exporting and importing your graphics etc.
The edit menu provides copy, cut,
paste, paste into, copy merged, fill, stroke, transform, define pattern, free
transform etc.
To Fill:
1. Select the area
2. Click on Edit
3. Click on Fill
4. Select the
color, type of fill (Background, foreground, 50% gray)
5. Click on OK
For Stroking or giving outline to your
selection:
1. Select the
area
2. Click on Edit
3. Click on
Stroke
4. Select the
width (in pixels), location (inside, outside, center), mode, opacity.
5. Click on OK
Under Transform we have Scale, Rotate,
Skew, Perspective, Distort, Flip Horizontal, Flip Vertical. With these options
available we can reshape, rotate the image.
The image menu provides you
the mode (Bitmap, Grayscale, RGB, CMYK, Lab color, Indexed color etc.), adjust,
image size, canvas size, calculation etc.
The layer menu provides for
inserting new layer, duplicating a layer, deleting a layer, layer options,
effects, type, group, ungroup, layer mask, merge layer etc.
For Masking:
1. Select the
area
2. Click on Layer
3. Click on Add
Layer Mask
4. Choose the
type of masking (Revel selection, hide selection)
5. Click on OK
Note: Add layer
mask works with the Layer only not with the Background.
The select menu provides the options
as all, deselect, reselect, inverse, modify, feather, grow, load selection,
save selection etc.
With the help of modify, feather and
grow we can give new look to the outlines of our image. Feather helps us while
creating Collages. Under modify we have border, expand, smooth, contract.
To make a new channel and use that
channel with “Lighting effect” filter do the following steps:
1. Select the
area by any of the selection tool
Or
2. Select the
whole layer by Select -> Load Selection ->Layer name -> OK
3. Select ->
Save Selection ->New Channel ->Give a name ->Save
4. Filter ->
Render -> Lighting Effect
5. Texture
channel -> Choose the channel (you have created)
6. Set either
Flat or Mountainous
7. OK
Under filter menu you will find
different types of filters which will help you to give special effects /
creating illusions with your drawing / image.
Under window menu bar you will
get to open different windows like, layer, path, history, brush, color,
swatches, actions, channels etc.
Transactions
Computerize Professional Accounting
A voucher is a document that contains details of a financial transaction and is required for recording the same into the books of accounts. For every transaction, you can use the appropriate Program voucher to enter the details into the ledgers and update the financial position of the company.
The voucher entry menus options are available under Transactions in the Gateway. The Payroll and Order Vouchers are available as separate options which can be enabled based on the requirements.
Part-1 Accounting Vouchers
1. Contra Entry
2. Payment Entry
3. Receipt Entry
4. Purchase Entry
5. Sales Entry
6. Printing Vouchers based on Due Date
7. Debit Note Entry
8. Credit Note Entry
9. Post-dated Cheque Entry
Part-2 Inventory Vouchers
1. Receipt note
2. Rejections In
3. Rejections Out
4. Material In
5. Material Out
6. Stock Journal
7. Physical Stock
Part-3 Optional and Non-Accounting Vouchers
1. Memorandum Voucher
2. Optional Vouchers
3. Reversing Journals
4. Post Dated Vouchers
Part-4 Order Processing
1. Enabling Order Processing
2. Viewing Order Position
3. Purchase Order Processing
4. Sales Order Processing
5. Job Order Processing
6. Viewing Order Position
Part-5 Advanced Voucher Entry
1. Using Additional Cost of Purchase
2. Using Tracking Numbers
3. Using Zero Valued Entries
4. Using different Actual and Billed Quantities
5. Using Batch wise details
6. Using Mfg. and expiry dates
7. Using Cost Categories and Cost Centres
8. Using Cost Centre Class
9. Using Multi-currency
Part-1
Accounting Vouchers
Part-2
Inventory Vouchers
Part-3
Optional And Non-Accounting Vouchers
Part-4
Order Processing
Part-5
Advanced Voucher Entry
Company Management
Company Feature
In Accounting Program, you can enable and use the available features as required for your company.
To enable company features
1. Go to F11: Features.
2. Select the required features in the Company Features menu.
3. Enable the required features.
4. Press Ctrl+A to accept.
Part-1
Accounting Management
Using the Accounting Features, you can enable various options required for making transactions in your business.
To enable the accounting features
1. Go to F11: Features > F1: Accounts. The Company Operations Alteration screen appears as shown below:
2. Enable the required options.
3. Press Ctrl+A to accept.
If inventory vouchers and features are not appearing for your company, set the option Maintain accounts only to No, to use the Inventory features.
General Accounting Features
ü Maintain accounts only- Enable this option if you do not have any inventory transactions.
ü Integrate accounts and inventory- Enable this option to include the stock or inventory balance from the inventory records. Provides a drill down to the stock registers from balance sheet. Disable this option to maintain accounts and inventory separately. Stock records often contain compensating errors caused by wrong allocation to items. This feature enables finalization of financial books without waiting for the reconciliation of stocks.
ü Use Income and Expenses A/c instead of Profit and Loss A/c- Enable this option to display income and expenses a/c as the menu item instead of profit and loss a/c in the Gateway of Tally menu. Income and expenses statements are generally used for non-trading accounts and profit and loss a/c are used for trading accounts.
ü Enable multi-currency– Enable this option to enable working with multiple currencies.
Outstanding Management
ü Maintain bill-wise details- Enable this option to display the option Maintain balances bill by bill in all ledgers created under sundry debtors and creditors. When you enter details of sales and purchases with the bill wise option activated, Accounting Program prompts you to identify the invoice with an appropriate reference number. The reference number can then be used to allocate payments to the correct invoice to maintain an accurate account of outstanding. Bill wise details for non-trading accounts is useful when one needs to track either an instalment to be paid or a loan amount to be received over a certain period of time.
ü Activate interest calculation- Enable this option to calculate interest automatically based on the interest rate and style of calculation specified. The advanced parameters are useful when interest rates change from time to time. Set this option to Yes to enable this function.
Cost/Profit Centres Management
ü Maintain payroll- Enable this option to maintain payroll information in Accounting Program for the selected company.
ü Maintain cost centres- Enable this option to maintain and allocate expenses to cost centres.
ü Use cost center for job costing- Enable this option to track all income and expenses.
ü Maintain more than one payroll or cost category- Enable this option to create more than one Payroll or Cost Category.
ü Use pre-defined cost centre allocations in transactions-Enable this option to define Cost Centre Allocations.
ü Show opening balance for revenue items in reports- Enable this option to display the opening balance in Cost Centre report for the cost centres which are allocated to the ledgers, grouped under Income and Expenses Group.
Invoicing Features
ü Enable invoicing- Enable this option to create Sales and Purchase vouchers in the invoice format.
ü Record purchases in invoice mode- Enable this option to enable voucher class option in purchase voucher type.
ü Use debit and credit notes- Enable this option to use the debit note and credit note voucher types.
ü Record credit notes in invoice mode- Enable this option to create credit notes in invoice mode.
ü Record debit notes in invoice mode- Enable this option to create debit notes in invoice mode.
Budgets & Scenario Management
ü Maintain budgets and controls- Enable this option to create multiple budgets. The Budgets menu option is displayed in Masters Info. > Accounts Info. menu.
ü Use reversing journals and optional vouchers- Enable this option to display the Scenario option in Accounts Info menu. You can create and alter scenarios. You can record Reversing Journal and make it Optional for the entries to not affect the books.
Banking Management
ü Enable cheque printing- Enable this option to use cheque printing.
ü Edit banking features- Enable this option to alter banking features.
ü Set/alter post-dated transaction features- Enable this option to record post-dated transactions and view related reports.
Other Management
ü Enable zero-valued transactions- Enable this option to allow zero valued transactions in vouchers.
ü Maintain multiple mailing details for company and ledgers- Enable this option to maintain multiple mailing details for your company and ledgers.
ü Set/alter company mailing details- Enable this option to create or alter Address Types.
ü Enable company log- Enable this option to print the company logo on the selected vouchers, reports, and invoices.
Part-2
Inventory Management
Using the Inventory Features, you can enable various options required for making transactions in your business.
To enable the inventory features
1. Go to F11: Features > F1: Inventory.
2. Enable the required options.
3. Press Ctrl+A to accept.
General
ü Integrate accounts and inventory- Enable this option to include the stock or inventory balance from the inventory records. Provides a drill down to the stock registers from balance sheet. Disable this option to maintain accounts and inventory separately. Stock records often contain compensating errors caused by wrong allocation to items. This feature enables finalization of financial books without waiting for the reconciliation of stocks.
ü Enable zero-valued transactions+ Enable this option to allow zero-valued transactions in Inventory vouchers.
Storage and Classification
ü Maintain multiple Godowns / Excise Units- Enable this option if you have more than one stock storage locations or godowns, and you want to track stock movement across these Locations.
ü Maintain stock categories- Enable this option to create and maintain stock categories
ü Maintain batch-wise details- Enable this option to maintain batch information pertaining to Stock Items. A new field Maintain in Batches is displayed in the Stock Item Creation screen.
ü Set expiry dates for batches- Enable this option to set expiry dates for the batches. This displays an additional field Use Expiry Dates in the Stock Item Creation screen.
ü Use separate actual and billed quantity columns- Enable this option to specify quantities, that are different from those delivered/ received, when invoicing.
Order Processing
ü Enable purchase order processing- Enable this option to create purchase orders. This feature can also be used for pre-closure of purchase order.
ü Enable sales order processing- Enable this option to create sales orders.
ü Enable job order processing- Enable this option to create job work out or in orders.
Invoicing
ü Enable invoicing- Enable this option to create Sales and Purchase vouchers in the invoice format.
ü Record purchases in invoice mode- Enable this option to enable voucher class option in purchase voucher type.
ü Use debit and credit notes- Enable this option to use the debit note and credit note voucher types.
ü Record credit notes in invoice mode- Enable this option to create credit notes in invoice mode.
ü Record debit notes in invoice mode- Enable this option to create debit notes in invoice mode.
Purchase Management
ü Track additional costs of purchase- Enable this option to obtain a break-up of purchase costs, without the need to separately debit ledger accounts for expenses.
Sales Management
ü Use multiple price levels- Enable this option to create multiple price levels.
Other Features
ü Use track ing numbers (enables delivery and receipt notes)- Enable this option to use tracking numbers to maintain the relation between delivery notes and invoices. This is available for both purchases and sales.
ü Use rejection inward and outward notes- Enable this option to record rejection of goods separately and not through a common debit note or credit note.
ü Use material in and out vouchers- Enable this option to record transfer of item quantity towards the party and transfer material from one Godown (Location) to the other.
ü Use cost tracking for stock item- Enable this option to analyse the cost involved for an item.
Part-3
Statutory And Taxation Management
Accounting Program supports the various taxes applicable in India. You can maintain accurate books of accounts and generate error-free returns by detecting the missing information in the transactions, if any, and correct them before filing returns.
You can use statutory and taxation features in Accounting Program by enabling the required options in the Company Operations Alteration screen.
To enable statutory and taxation features
Part-4
Audit Management
Enable this option to use auditing features. The option F5: Audit Features is available only in the Accounting Program Auditor Edition.
To enable audit features
Company Configuration
Configurations are application centric configurations that are present across all screens of Accounting Program. These configurations can be changed and managed any number of times to suit changing needs.
Configuration options, affect all the companies maintained in the same Accounting Program directory and setting the configuration for one company will affect the configuration of other companies in that particular data directory.
Part-1
Voucher Entry Configuration
You can customise the voucher entries in Accounting Program, both the accounting and inventory vouchers, by enabling required options in the Voucher Configuration.
1. Go to Configure > Voucher Entry. The Voucher Configuration screen appears:
2. Enable the required options.
3. Press Ctrl+A to accept.
Accounts
ü Skip Date field during creation for faster entry-By default, the cursor skips the Date field during Voucher creation. If you do not want to skip the date field then set this option to No.
ü Use single entry mode for payment/receipt/contra vouchers- By default, Accounting Program displays single entry mode for payment/receipt/contra entry. If you want to display it in double entry mode, then set this option to No.
ü Use payment/receipt as contra voucher- Enable this option to use payment and receipt voucher as contra voucher.
ü Use Cr/Dr instead of To/By during entry- Enable this option to change To/By to Cr/Dr in the vouchers.
ü Use cheque printing for contra voucher- Enable this option to print the cheques from contra voucher while making the interbank transfers and cash withdrawals.
ü Warn on negative cash balance- By Default, Accounting Program displays a Negative Cash balance warning Message. If you set it to No, the error message will not be displayed.
ü Preallocate bills for payment/receipt/journal voucher- Enable this option to preallocate the bills before specifying the ledger amount.
ü Allow cash accounts in journal vouchers- Enable this option to select cash and also bank account in Journal voucher.
ü Allow expenses/fixed assets in purchase vouchers- Enable this option to select the expenses and also fixed asset ledger in purchase voucher.
ü Show inventory details- By default, Accounting Program displays inventory details in the voucher entry screen. If you set it to No, the inventory details will not be displayed.
ü Show table of bills for selection- By default, pending bills list of a ledger account are displayed in the voucher entry screen. If you set it to No, the pending bills list will not be displayed.
ü Show bill-wise details- By default, Bill-wise details of a ledger account are displayed in the Voucher entry screen. If you set it to No, Bill wise details will not be displayed
ü Show current balances of ledgers- By default, the ledger current balance up to last voucher entry date are displayed. If you set it to No, the ledger current balance will not be displayed
ü Show balance as on voucher date- By default, the ledger current balance up to last voucher entry date are displayed. If you set it to Yes, it will display the ledger balance up to current voucher entry date
ü Show forex gain/loss as on voucher date- By default, the Forex Gain/Loss balance up to the last voucher entry date are displayed. If you set it to Yes, it will display the Forex Gain/Loss balance up to current voucher entry date
Inventory
ü Provide reference number in stock journal- Enable this option to add the voucher reference field in Stock Journal also.
ü Show compound unit of item based on rate- Enable this option to show the compound unit of item based on the unit provided in the Rate Per column.
ü Show full details of compound unit – Enable this option to display full details of compound unit in the Quantity field. If Kgs is typed in Rate Per field, the Quantity field will display as 12 Kgs.250 grms.
ü Warn on negative stock balance- By default, a warning message is displayed for negative stock balance. If you set it to No, the error message will not be displayed.
ü Allow use of expiry batches for all stock items- By default, the expiry batches in the list of active batches during voucher entry are displayed. If you set it to No, expiry batches will not be displayed in the List of Active batches.
ü Show balances as on voucher date- By default, the stock item balance up to the last voucher entry date are displayed. If you set it to Yes, it will display the Stock Item balance up to current voucher entry date.
ü Show Godown-wise details- By default, the Godown details in rejection in/out vouchers are displayed. If you set it to No, the godown details will not be displayed in the rejection in/out vouchers.
ü Show batch-wise details- Enable this option to display batch information of stock items during voucher entry. If you set it to No, the Batch-Wise details will not be displayed.
Payroll
ü Allow cost centre allocation in payroll voucher- Enable this option to allow cost centre allocation in the payroll vouchers.
Statutory
ü Allow modification of tax details- Enable this option to modify tax details.
Part-2
Invoice, Delivery Note, or Order Configuration
You can customise your invoice, delivery notes, and other order vouchers using the options available in the Invoice Configuration screen. This involves specifying or automatically allocating the invoice value to a bill reference.
To change the invoice configuration
1. Go to F12: Configure > Invoice / Orders Entry. The Invoice Configuration screen appears:
2. Enable the required options.
3. Press Ctrl+A to accept.
General Options
ü Enable supplementary details- Enable this option to view the Party Details screen, when a party ledger is selected during invoice entry. Despatch details, order details, and buyer’s details can be recorded.
ü Allow separate buyer and consignee names- Enable this option to enter buyer and consignee details separately in the Party Details screen.
ü Allow modification of all fields during entry- Default order/delivery note entries appearing in the invoice can be changed during invoice entry. Enable this option to permit modification of all fields.
ü Use common Ledger A/c for item allocation- Enable this option to allocate all the items selected in the invoice to a common sales or purchase account. If each item in the invoice has to be allocated to different ledger accounts, then this option should be set to No.
ü Use defaults for bill allocations- Set this option to No, to enter the reference number, or select the required bill while saving an invoice. Set this option to Yes, to automatically display the invoice number as the bill reference name. The credit period specified in the party ledger master will be automatically captured by default in the bill wise details screen.
ü Provide additional descriptions for item name- Enable this option to specify description for each item selected in the invoice.
ü Provide additional descriptions for ledger name- Enable this option to specify the description for each Ledger selected in the Accounting invoice entries.
ü Consolidate stock items with same rates- Enable this option to consolidate the stock items having same rates in Invoice/Challans.
ü Show compound unit of item based on rate- Enable this option to show the compound unit of item based on the unit provided in the Rate Per column.
ü Show full details of compound unit- Enable this option to display full details of compound unit in the Quantity field. If Kgs is typed in Rate Per field, the Quantity field will display as 12 Kgs.250 grms.
ü Show turnover achieved with customer- Enable this option to view the turnover achieved till date with a particular customer.
Exporter’s Options
ü Provide export shipping details- Enable this option to enter export details for the invoice in the Supplementary details screen.
You can enter the following details:
● Place of Receipt
● Vessel / Flight No. (the transport used to send the goods)
● Port of Loading (from where the goods are despatched)
● Port of Discharge (where the goods will be finally offloaded)
● Country To (to which country the goods are being sent)
ü Provide marks and numbers./container no.- Enable this option to specify Marks for every item selected in the invoice.
ü Provide number and kind of packages- Enable this option to specify Num. Packages for every item selected in the invoice.
Inventory
ü Warn on negative stock balance- Enable this option to warn if the item selected reaches a negative balance.
ü Warn on duplicate order number- Enable this option to display a warning message to notify when an order number is repeated.
ü Use expired batches for all stock items- By default, this option is set to Yes. Disable this option to not include expired batches in the list of batches displayed at the time of entry.
ü Provide complete accounting allocations in order/delivery note- Enable this option for faster data entry at the time of entering sales/purchase invoices against the deliver or receipt notes.
Statutory
ü Calculate tax on current sub-total- Enable this option to calculate tax on the current subtotal value and not on inventory total value.
ü Allow modification of tax details- Enable this option to modify tax details.
Open Python Program File
Open Fundamental Program File
In this file you will get learn the following topics.
Computer, Data processing, Characteristic features of computers, Computers’ evolution to their present form, Computer generations, Characteristic features of each computer generation
Basic operations performed by all types of computer systems, Basic organization of a computer system, Input unit and its functions, Output unit and its functions, Storage unit and its functions, Types of storage used in a computer system
Non-positional number system, Positional number system, Decimal number system, Binary number system, Octal number system, Hexadecimal number system
Computer data, Computer codes: representation of data in binary, Most commonly used computer codes, Collating sequence:
Reasons for using binary instead of decimal numbers, Basic arithmetic operations using binary numbers, Addition (+), Subtraction (-), Multiplication (*), Division (/)
Internal structure of processor, Memory structure, Determining the speed of a processor, Different types of processors available, Determining the capacity of a memory, Different types of memory available, Several other terms related to the processor and main memory of a computer system
Secondary storage devices and their need, Classification of commonly used secondary storage devices, Difference between sequential and direct access storage devices, Basic principles of operation, types, and uses of popular secondary storage devices such as magnetic tape, magnetic disk, and optical disk
Input/Output (I/O) devices, Commonly used input devices, Commonly used output devices, Other concepts related to I/O devices, Term “Software” and its relationship with “Hardware”, Various types of software and their examples, Relationship among hardware, system software, application software, and users of a computer system, Different ways of acquiring software, Various steps involved in software development, Firmware, Middleware
Programs must be planned before they are written, Algorithm, Flowchart, Pseudocode, Plan the logic of a computer program, Commonly used tools for program planning and their use
Computer languages or programming languages, Three broad categories of programming languages – machine, assembly, and high-level languages, Commonly used programming language tools such as assembler, compiler, linker, and interpreter, Concepts of object-oriented programming languages, Some popular programming languages such as FORTRAN, COBOL, BASIC, Pascal, C, C++, C#, Java, RPG, LISP and SNOBOL, Related concepts such as Subprogram, Characteristics of a good programming language, and factors to consider while selecting a language for coding an application
Definition and need for operating system, Main functions of an operating system, Commonly used mechanisms for:, Process management, Memory management, File management, Security, Command interpretation module, Some commonly used OS capability enhancement software, Some popular operating systems
Word-processing package, Spreadsheet package, Graphics package, Personal assistance package
Classifications of computers, Common types of computers today, Characteristic features of various types of computers in use today
Operating System
Open Operating System Program File
Open Word-Processing Program File
In this file you will get learn the following topics.
Create and format documents
Basic tasks in Word, create a fillable form, Set page margins, Change the line spacing, Change the font color (text color), Add a “Draft” watermark to your document, Add a picture as a background watermark
Headers and footers
Add a header or footer, Add images to a header or footer, Add page numbers to a header or footer in Word for Windows, Delete or change a header or footer on a single page, Insert the file name in a footer
Page numbers
Add page numbers, Add page numbers to a header or footer, Add different page numbers or number formats to different sections, Start page numbering later in your document, Add page number X of Y, Delete page numbers
Tables of contents
Create a table of contents, Format or customize a table of contents, Update a table of contents
Links, images, and graphics
Create or edit a hyperlink, Add or delete bookmarks in a Word document, Remove a hyperlink, Insert pictures, Insert a screenshot or screen clipping, Learn about SmartArt Graphics, Insert a check mark or other symbol
Review a document
Track Changes, Accept tracked changes, Track changes in Word, Change your user name and initials, Keep Track Changes on with a password, Turn off track changes, Check spelling and grammar in Office, Add words to your spell check dictionary
Mail merge
Mail merge with an Excel spreadsheet, Use mail merge for email, Use mail merge to personalize letters, Mail merge for labels, Mail merge for envelopes, Format your mail merge contacts in an Excel spreadsheet, Set up a mail merge list in Word
Share and print
Share your document, Collaborate on Word documents with real-time coauthoring, Print a document, Shrink text to fit, Change page orientation to landscape or portrait, Save or convert to PDF or XPS, Add a “Draft” watermark to your document, Create a fillable form, Test your document’s readability
Accessibility
Creating accessible Word documents, Create accessible PDFs, Check for accessibility issues, Keyboard shortcuts for Word, Keyboard shortcuts for SmartArt graphics, Customize keyboard shortcuts, Use a screen reader to explore and navigate Word
And much more…..
Open Spreadsheet Program File
In this file you will get learn the following topics.
Create, Save, Analyze and format in Excel
Rows, columns & cells
Insert or delete, Freeze panes to lock, Hide or show, Filter for unique values or remove duplicate values, Split text into different columns with the Convert Text to Columns Wizard, Create a list of sequential dates, Move or copy cells and cell contents, Resize a table, Find or replace text and numbers on a worksheet, Merge and unmerge, Apply data validation to cells, Import or export text (.txt or .csv) files
Formulas & functions
Learn these top skills to create your own formulas and functions.
Formatting
Available number, Conditional formatting, Align or rotate text in a cell, Change the format of a cell, Copy cell formatting with the Format Painter, Add a watermark , Display or hide zero values, Create or delete a custom number format
Tables & charts
Learn these top skills to create your own tables and charts.
PivotTables
Create a PivotTable to analyze worksheet data, Use the Field List to arrange fields in a PivotTable, Group or ungroup data in a PivotTable, Filter data in a PivotTable, Create a PivotChart
And much more…..
Open Multimedia Program File
In this file you will get learn the following topics.
Get started
Basic tasks for creating a PowerPoint presentation, Create a basic presentation in four steps
Create a presentation
Add, rearrange, and delete slides, Change the size of your slides, Use portrait slide orientation for your presentation, Add a hyperlink to a slide, Basic tasks for creating a PowerPoint presentation, Format text as superscript or subscript, Use keyboard shortcuts to create your presentation, Save your presentation file
Deliver a presentation
Print slides with or without speaker notes, Start the presentation and see your notes in Presenter view, Create a self-running presentation, Add speaker notes to your slides, View your speaker notes as you deliver your slide show, Use keyboard shortcuts to deliver your presentation
Design your slides
Create professional slide layouts with PowerPoint Designer , Create and save a PowerPoint template, Create your own theme in PowerPoint, Combining colors in PowerPoint – Mistakes to avoid, Save a slide design (theme) as a template, Slide masters, layouts, and themes, Remove or change the current theme, Use multiple themes in one presentation, Change the fonts, Add a background picture (or watermark) to slides
Add formatting and effects
Animate text or objects, Apply multiple animation effects to more than one object, Format the background color of slides, Add, change, or remove transitions between slides, Use the Morph transition , Play music and other sounds automatically when a slide appears
Add pictures, graphics, or data
Insert clip art, Insert pictures, Insert Excel data in PowerPoint, Use charts and graphs in your presentation, Make or find pictures in Office
Insert audio or video
Turn your presentation into a video, Video and audio file formats supported in PowerPoint, Play music for the duration of your slide show, Add or delete audio in your presentation, Insert or link to a video on YouTube, Add an animated GIF to a slide, Add and play a video in a presentation
Work on a presentation with others
Work together on PowerPoint presentations, Use comments in a presentation, Track changes in your presentation, Use e-mail to send a presentation or a link to a presentation, Prepare to distribute a presentation, Turn your presentation into a video, Open a presentation created in a different version of PowerPoint, Compatibility Checker, Help prevent changes to a final version of a file, Remove hidden data and personal information by inspecting presentations, View or change the properties of an Office file
Add headers and footers
Slides: slide numbers, date, and footer, Handouts: page numbers, footers, and headers, Notes pages: page numbers, footers, and headers, Change the fonts in a footer on a slide
Using different file types
View or change the properties for an Office file, Save your presentation file, Save a presentation in a different file format, Insert PDF file content into a PowerPoint presentation, Use PowerPoint to open or save a presentation in the OpenDocument Presentation (.odp) format
Open Database Management System Program File
In this file you will get learn the following topics.
Design Tables
Introduction to tables, , Guidelines for naming fields, controls, and objects, Control data entry formats with input masks, Normalize your data using the Table Analyzer, Add or change a table’s primary key, Restrict data input by using a validation rule, Guide to table relationships, Add a calculated field to a table, Data types for Access desktop databases, Create and use an index to improve performance
Understand Queries
Introduction to queries, Examples of using dates as criteria in Access queries, Examples of Access query criteria, Create and run an update query, Use parameters to ask for input when running a query, Create a simple select query, Create a make table query, Create and run a delete query, Add records to a table by using an append query
Create Forms
Create an Access form, Create a list of choices by using a list box or combo box, Create a form that contains a subforum (a one-to-many form), Set default values for fields or controls, Create a navigation form, Display column totals in a datasheet using a Totals row, Apply a filter to view select records in an Access database, Create a form by using the Form Wizard, Create a form by using the Form tool
Create Reports
Introduction to reports in Access, Create a grouped or summary report, Set print options, Insert a page break control in an Access report, Video: Use conditional formatting on reports, Set the record source for a report, Filter data in a report, Preview and print a report
Use Expressions
Use the Expression Builder, Introduction to expressions, learn to build an expression, Guide to expression syntax, Examples of expressions, String functions and how to use them, Access Functions (by category)
Work with External Data
Import or link to data in another Access database, Import or link to data in an Excel workbook, Link to or import from an SQL Server database, import from or link data to a SharePoint list, Import or link to data in a text file, Export data to Excel, Use mail merge to send data to Word
Set Global Options
Decide whether to trust a database, Protect your data with backup and restore processes, Customize the Navigation Pane, Set user options for the current database, Set name AutoCorrect options, Encrypt a database by using a database password, Split an Access database, Show or hide the Navigation Pane in Access, Compact and repair database files, Set the default format options for datasheets
Keyboard Shortcuts
And much more…..
Part-1
Data Communication and Computer Network (DCN)
This subject has studied basics of Data Communication and Computer Network (DCN) and will also through various advance concepts related to Data Communication and Computer Network..
Data communications
Data communications refers to the transmission of this digital data between two or more computers and a computer network or data network is a telecommunications network that allows computers to exchange data. The physical connection between networked computing devices is established using either cable media or wireless media. The best-known computer network is the Internet.
Computer Network Introduction
A system of interconnected computers and computerized peripherals such as printers is called computer network. This interconnection among computers facilitates information sharing among them. Computers may connect to each other by either wired or wireless media.
Classification of Computer Networks
Computer networks are classified based on various factors.They includes:
- Geographical span
- Inter-connectivity
- Administration
- Architecture
Geographical Span
Geographically a network can be seen in one of the following categories:
- It may be spanned across your table, among Bluetooth enabled devices,. Ranging not more than few meters.
- It may be spanned across a whole building, including intermediate devices to connect all floors.
- It may be spanned across a whole city.
- It may be spanned across multiple cities or provinces.
- It may be one network covering whole world.
Inter-Connectivity
Components of a network can be connected to each other differently in some fashion. By connectedness we mean either logically , physically , or both ways.
- Every single device can be connected to every other device on network, making the network mesh.
- All devices can be connected to a single medium but geographically disconnected, created bus like structure.
- Each device is connected to its left and right peers only, creating linear structure.
- All devices connected together with a single device, creating star like structure.
- All devices connected arbitrarily using all previous ways to connect each other, resulting in a hybrid structure.
Administration
From an administrator’s point of view, a network can be private network which belongs a single autonomous system and cannot be accessed outside its physical or logical domain.A network can be public which is accessed by all.
Network Architecture
Computer networks can be discriminated into various types such as Client-Server, peer-to-peer or hybrid, depending upon its architecture.
- There can be one or more systems acting as Server. Other being Client, requests the Server to serve requests. Server takes and processes request on behalf of Clients.
- Two systems can be connected Point-to-Point, or in back-to-back fashion. They both reside at the same level and called peers.
- There can be hybrid network which involves network architecture of both the above types.
Network Applications
Computer systems and peripherals are connected to form a network. They provide numerous advantages:
- Resource sharing such as printers and storage devices
- Exchange of information by means of e-Mails and FTP
- Information sharing by using Web or Internet
- Interaction with other users using dynamic web pages
- IP phones
- Video conferences
- Parallel computing
- Instant messaging
Computer Network Types
Generally, networks are distinguished based on their geographical span. A network can be as small as distance between your mobile phone and its Bluetooth headphone and as large as the internet itself, covering the whole geographical world,
Personal Area Network
A Personal Area Network (PAN) is smallest network which is very personal to a user. This may include Bluetooth enabled devices or infra-red enabled devices. PAN has connectivity range up to 10 meters. PAN may include wireless computer keyboard and mouse, Bluetooth enabled headphones, wireless printers and TV remotes.
For example, Piconet is Bluetooth-enabled Personal Area Network which may contain up to 8 devices connected together in a master-slave fashion.
Local Area Network
A computer network spanned inside a building and operated under single administrative system is generally termed as Local Area Network (LAN). Usually, LAN covers an organization’ offices, schools, colleges or universities. Number of systems connected in LAN may vary from as least as two to as much as 16 million.
LAN provides a useful way of sharing the resources between end users. The resources such as printers, file servers, scanners, and internet are easily sharable among computers.
LANs are composed of inexpensive networking and routing equipment. It may contains local servers serving file storage and other locally shared applications. It mostly operates on private IP addresses and does not involve heavy routing. LAN works under its own local domain and controlled centrally.
LAN uses either Ethernet or Token-ring technology. Ethernet is most widely employed LAN technology and uses Star topology, while Token-ring is rarely seen.
LAN can be wired, wireless, or in both forms at once.
Metropolitan Area Network
The Metropolitan Area Network (MAN) generally expands throughout a city such as cable TV network. It can be in the form of Ethernet, Token-ring, ATM, or Fiber Distributed Data Interface (FDDI).
Metro Ethernet is a service which is provided by ISPs. This service enables its users to expand their Local Area Networks. For example, MAN can help an organization to connect all of its offices in a city.
Backbone of MAN is high-capacity and high-speed fiber optics. MAN works in between Local Area Network and Wide Area Network. MAN provides uplink for LANs to WANs or internet.
Wide Area Network
As the name suggests, the Wide Area Network (WAN) covers a wide area which may span across provinces and even a whole country. Generally, telecommunication networks are Wide Area Network. These networks provide connectivity to MANs and LANs. Since they are equipped with very high-speed backbone, WANs use very expensive network equipment.
WAN may use advanced technologies such as Asynchronous Transfer Mode (ATM), Frame Relay, and Synchronous Optical Network (SONET). WAN may be managed by multiple administration.
Internetwork
A network of networks is called an internetwork, or simply the internet. It is the largest network in existence on this planet. The internet hugely connects all WANs and it can have connection to LANs and Home networks. Internet uses TCP/IP protocol suite and uses IP as its addressing protocol. Present day, Internet is widely implemented using IPv4. Because of shortage of address spaces, it is gradually migrating from IPv4 to IPv6.
Internet enables its users to share and access enormous amount of information worldwide. It uses WWW, FTP, email services, audio and video streaming etc. At huge level, internet works on Client-Server model.
Internet uses very high speed backbone of fiber optics. To inter-connect various continents, fibers are laid under sea known to us as submarine communication cable.
Internet is widely deployed on World Wide Web services using HTML linked pages and is accessible by client software known as Web Browsers. When a user requests a page using some web browser located on some Web Server anywhere in the world, the Web Server responds with the proper HTML page. The communication delay is very low.
Internet is serving many proposes and is involved in many aspects of life. Some of them are:
- Web sites
- Instant Messaging
- Blogging
- Social Media
- Marketing
- Networking
- Resource Sharing
- Audio and Video Streaming
Network LAN Technologies
The various LAN technologies in brief:
Ethernet
Ethernet is a widely deployed LAN technology. This technology was invented by Bob Metcalfe and D.R. Boggs in the year 1970. It was standardized in IEEE 802.3 in 1980.
Ethernet shares media. Network which uses shared media has high probability of data collision. Ethernet uses Carrier Sense Multi Access/Collision Detection (CSMA/CD) technology to detect collisions. On the occurrence of collision in Ethernet, all its hosts roll back, wait for some random amount of time, and then re-transmit the data.
Ethernet connector is, network interface card equipped with 48-bits MAC address. This helps other Ethernet devices to identify and communicate with remote devices in Ethernet.
Traditional Ethernet uses 10BASE-T specifications. The number 10 depicts 10MBPS speed, BASE stands for baseband, and T stands for Thick Ethernet. 10BASE-T Ethernet provides transmission speed up to 10MBPS and uses coaxial cable or Cat-5 twisted pair cable with RJ-45 connector. Ethernet follows star topology with segment length up to 100 meters. All devices are connected to a hub/switch in a star fashion.
Fast-Ethernet
To encompass need of fast emerging software and hardware technologies, Ethernet extends itself as Fast-Ethernet. It can run on UTP, Optical Fiber, and wirelessly too. It can provide speed up to 100 MBPS. This standard is named as 100BASE-T in IEEE 803.2 using Cat-5 twisted pair cable. It uses CSMA/CD technique for wired media sharing among the Ethernet hosts and CSMA/CA (CA stands for Collision Avoidance) technique for wireless Ethernet LAN.
Fast Ethernet on fiber is defined under 100BASE-FX standard which provides speed up to 100 MBPS on fiber. Ethernet over fiber can be extended up to 100 meters in half-duplex mode and can reach maximum of 2000 meters in full-duplex over multimode fibers.
Giga-Ethernet
After being introduced in 1995, Fast-Ethernet could enjoy its high-speed status only for 3 years till Giga-Ethernet introduced. Giga-Ethernet provides speed up to 1000 mbits/seconds. IEEE802.3ab standardize Giga-Ethernet over UTP using Cat-5, Cat-5e and Cat-6 cables. IEEE802.3ah defines Giga-Ethernet over Fiber.
Virtual LAN
LAN uses Ethernet which in turn works on shared media. Shared media in Ethernet create one single Broadcast domain and one single Collision domain. Introduction of switches to Ethernet has removed single collision domain issue and each device connected to switch works in its separate collision domain. But even Switches cannot divide a network into separate Broadcast domains.
Virtual LAN is a solution to divide a single Broadcast domain into multiple Broadcast domains. Host in one VLAN cannot speak to a host in another. By default, all hosts are placed into the same VLAN.
In this diagram, different VLANs are depicted in different color codes. Hosts in one VLAN, even if connected on the same Switch cannot see or speak to other hosts in different VLANs. VLAN is Layer-2 technology which works closely on Ethernet. To route packets between two different VLANs a Layer-3 device such as Router is required.
A Network Topology is the arrangement with which computer systems or network devices are connected to each other. Topologies may define both physical and logical aspect of the network. Both logical and physical topologies could be same or different in a same network.
Point-to-Point
Point-to-point networks contains exactly two hosts such as computer, switches or routers, servers connected back to back using a single piece of cable. Often, the receiving end of one host is connected to sending end of the other and vice-versa.
If the hosts are connected point-to-point logically, then may have multiple intermediate devices. But the end hosts are unaware of underlying network and see each other as if they are connected directly.
Bus Topology
In case of Bus topology, all devices share single communication line or cable. Bus topology may have problem while multiple hosts sending data at the same time. Therefore, Bus topology either uses CSMA/CD technology or recognizes one host as Bus Master to solve the issue. It is one of the simple forms of networking where a failure of a device does not affect the other devices. But failure of the shared communication line can make all other devices stop functioning.
Both ends of the shared channel have line terminator. The data is sent in only one direction and as soon as it reaches the extreme end, the terminator removes the data from the line.
Star Topology
All hosts in Star topology are connected to a central device, known as hub device, using a point-to-point connection. That is, there exists a point to point connection between hosts and hub. The hub device can be any of the following:
- Layer-1 device such as hub or repeater
- Layer-2 device such as switch or bridge
- Layer-3 device such as router or gateway
As in Bus topology, hub acts as single point of failure. If hub fails, connectivity of all hosts to all other hosts fails. Every communication between hosts, takes place through only the hub. Star topology is not expensive as to connect one more host, only one cable is required and configuration is simple.
Ring Topology
In ring topology, each host machine connects to exactly two other machines, creating a circular network structure. When one host tries to communicate or send message to a host which is not adjacent to it, the data travels through all intermediate hosts. To connect one more host in the existing structure, the administrator may need only one more extra cable.
Failure of any host results in failure of the whole ring.Thus, every connection in the ring is a point of failure. There are methods which employ one more backup ring.
Mesh Topology
In this type of topology, a host is connected to one or multiple hosts .This topology has hosts in point-to-point connection with every other host or may also have hosts which are in point-to-point connection to few hosts only.
Hosts in Mesh topology also work as relay for other hosts which do not have direct point-to-point links. Mesh technology comes into two types:
- Full Mesh: All hosts have a point-to-point connection to every other host in the network. Thus for every new host n(n-1)/2 connections are required. It provides the most reliable network structure among all network topologies.
- Partially Mesh: Not all hosts have point-to-point connection to every other host. Hosts connect to each other in some arbitrarily fashion. This topology exists where we need to provide reliability to some hosts out of all.
Tree Topology
Also known as Hierarchical Topology, this is the most common form of network topology in use presently. This topology imitates as extended Star topology and inherits properties of bus topology.
This topology divides the network in to multiple levels/layers of network. Mainly in LANs, a network is bifurcated into three types of network devices. The lowermost is access-layer where computers are attached. The middle layer is known as distribution layer, which works as mediator between upper layer and lower layer. The highest layer is known as core layer, and is central point of the network, i.e. root of the tree from which all nodes fork.
All neighbouring hosts have point-to-point connection between them. Similar to the Bus topology, if the root goes down, then the entire network suffers even. though it is not the single point of failure. Every connection serves as point of failure, failing of which divides the network into unreachable segment.
Daisy Chain
This topology connects all the hosts in a linear fashion. Similar to Ring topology, all hosts are connected to two hosts only, except the end hosts. Means, if the end hosts in daisy chain are connected then it represents Ring topology.
Each link in daisy chain topology represents single point of failure. Every link failure splits the network into two segments. Every intermediate host works as relay for its immediate hosts.
Hybrid Topology
A network structure whose design contains more than one topology is said to be hybrid topology. Hybrid topology inherits merits and demerits of all the incorporating topologies.
The above picture represents an arbitrarily hybrid topology. The combining topologies may contain attributes of Star, Ring, Bus, and Daisy-chain topologies. Most WANs are connected by means of Dual-Ring topology and networks connected to them are mostly Star topology networks. Internet is the best example of largest Hybrid topology
Computer Network Models
Networking engineering is a complicated task, which involves software, firmware, chip level engineering, hardware, and electric pulses. To ease network engineering, the whole networking concept is divided into multiple layers. Each layer is involved in some particular task and is independent of all other layers. But as a whole, almost all networking tasks depend on all of these layers. Layers share data between them and they depend on each other only to take input and send output.
Layered Tasks
In layered architecture of Network Model, one whole network process is divided into small tasks. Each small task is then assigned to a particular layer which works dedicatedly to process the task only. Every layer does only specific work.
In layered communication system, one layer of a host deals with the task done by or to be done by its peer layer at the same level on the remote host. The task is either initiated by layer at the lowest level or at the top most level. If the task is initiated by the-top most layer, it is passed on to the layer below it for further processing. The lower layer does the same thing, it processes the task and passes on to lower layer. If the task is initiated by lower most layer, then the reverse path is taken.
Every layer clubs together all procedures, protocols, and methods which it requires to execute its piece of task. All layers identify their counterparts by means of encapsulation header and tail.
OSI Model
Open System Interconnect is an open standard for all communication systems. OSI model is established by International Standard Organization (ISO). This model has seven layers:
- Application Layer: This layer is responsible for providing interface to the application user. This layer encompasses protocols which directly interact with the user.
- Presentation Layer: This layer defines how data in the native format of remote host should be presented in the native format of host.
- Session Layer: This layer maintains sessions between remote hosts. For example, once user/password authentication is done, the remote host maintains this session for a while and does not ask for authentication again in that time span.
- Transport Layer: This layer is responsible for end-to-end delivery between hosts.
- Network Layer: This layer is responsible for address assignment and uniquely addressing hosts in a network.
- Data Link Layer: This layer is responsible for reading and writing data from and onto the line. Link errors are detected at this layer.
- Physical Layer: This layer defines the hardware, cabling wiring, power output, pulse rate etc.
Internet Model
Internet uses TCP/IP protocol suite, also known as Internet suite. This defines Internet Model which contains four layered architecture. OSI Model is general communication model but Internet Model is what the internet uses for all its communication. The internet is independent of its underlying network architecture so is its Model. This model has the following layers:
- Application Layer: This layer defines the protocol which enables user to interact with the network. For example, FTP, HTTP etc.
- Transport Layer: This layer defines how data should flow between hosts. Major protocol at this layer is Transmission Control Protocol (TCP). This layer ensures data delivered between hosts is in-order and is responsible for end-to-end delivery.
- Internet Layer: Internet Protocol (IP) works on this layer. This layer facilitates host addressing and recognition. This layer defines routing.
- Link Layer: This layer provides mechanism of sending and receiving actual data. Unlike its OSI Model counterpart, this layer is independent of underlying network architecture and hardware.
Computer Network Security
During initial days of internet, its use was limited to military and universities for research and development purpose. Later when all networks merged together and formed internet, the data use ds to travel through public transit network. Common people may send the data that can be highly sensitive such as their bank credentials, username and passwords, personal documents, online shopping details, or confidential documents.
All security threats are intentional i.e. they occur only if intentionally triggered. Security threats can be divided into the following categories:
- Interruption
Interruption is a security threat in which availability of resources is attacked. For example, a user is unable to access its web-server or the web-server is hijacked.
- Privacy-Breach
In this threat, the privacy of a user is compromised. Someone, who is not the authorized person is accessing or intercepting data sent or received by the original authenticated user.
- Integrity
This type of threat includes any alteration or modification in the original context of communication. The attacker intercepts and receives the data sent by the sender and the attacker then either modifies or generates false data and sends to the receiver. The receiver receives the data assuming that it is being sent by the original Sender.
- Authenticity
This threat occurs when an attacker or a security violator, poses as a genuine person and accesses the resources or communicates with other genuine users.
No technique in the present world can provide 100% security. But steps can be taken to secure data while it travels in unsecured network or internet. The most widely used technique is Cryptography.
Cryptography is a technique to encrypt the plain-text data which makes it difficult to understand and interpret. There are several cryptographic algorithms available present day as described below:
- Secret Key
- Public Key
- Message Digest
Secret Key Encryption
Both sender and receiver have one secret key. This secret key is used to encrypt the data at sender’s end. After the data is encrypted, it is sent on the public domain to the receiver. Because the receiver knows and has the Secret Key, the encrypted data packets can easily be decrypted.
Example of secret key encryption is Data Encryption Standard (DES). In Secret Key encryption, it is required to have a separate key for each host on the network making it difficult to manage.
Public Key Encryption
In this encryption system, every user has its own Secret Key and it is not in the shared domain. The secret key is never revealed on public domain. Along with secret key, every user has its own but public key. Public key is always made public and is used by Senders to encrypt the data. When the user receives the encrypted data, he can easily decrypt it by using its own Secret Key.
Example of public key encryption is Rivest-Shamir-Adleman (RSA).
Message Digest
In this method, actual data is not sent, instead a hash value is calculated and sent. The other end user, computes its own hash value and compares with the one just received.If both hash values are matched, then it is accepted otherwise rejected.
Example of Message Digest is MD5 hashing. It is mostly used in authentication where user password is cross checked with the one saved on the server.
Physical Layer Introduction
Physical layer in the OSI model plays the role of interacting with actual hardware and signalling mechanism. Physical layer is the only layer of OSI network model which actually deals with the physical connectivity of two different stations. This layer defines the hardware equipment, cabling, wiring, frequencies, pulses used to represent binary signals etc.
Physical layer provides its services to Data-link layer. Data-link layer hands over frames to physical layer. Physical layer converts them to electrical pulses, which represent binary data. The binary data is then sent over the wired or wireless media.
Signals
When data is sent over physical medium, it needs to be first converted into electromagnetic signals. Data itself can be analog such as human voice, or digital such as file on the disk.Both analog and digital data can be represented in digital or analog signals.
- Digital Signals
Digital signals are discrete in nature and represent sequence of voltage pulses. Digital signals are used within the circuitry of a computer system.
- Analog Signals
Analog signals are in continuous wave form in nature and represented by continuous electromagnetic waves.
Transmission Impairment
When signals travel through the medium they tend to deteriorate. This may have many reasons as given:
- Attenuation
For the receiver to interpret the data accurately, the signal must be sufficiently strong. When the signal passes through the medium, it tends to get weaker.As it covers distance, it loses strength.
- Dispersion
As signal travels through the media, it tends to spread and overlaps. The amount of dispersion depends upon the frequency used.
- Delay distortion
Signals are sent over media with pre-defined speed and frequency. If the signal speed and frequency do not match, there are possibilities that signal reaches destination in arbitrary fashion. In digital media, this is very critical that some bits reach earlier than the previously sent ones.
- Noise
Random disturbance or fluctuation in analog or digital signal is said to be Noise in signal, which may distort the actual information being carried. Noise can be characterized in one of the following class:
- Thermal Noise
Heat agitates the electronic conductors of a medium which may introduce noise in the media. Up to a certain level, thermal noise is unavoidable.
- Intermodulation
When multiple frequencies share a medium, their interference can cause noise in the medium. Intermodulation noise occurs if two different frequencies are sharing a medium and one of them has excessive strength or the component itself is not functioning properly, then the resultant frequency may not be delivered as expected.
- Crosstalk
This sort of noise happens when a foreign signal enters into the media. This is because signal in one medium affects the signal of second medium.
- Impulse
This noise is introduced because of irregular disturbances such as lightening, electricity, short-circuit, or faulty components. Digital data is mostly affected by this sort of noise.
Transmission Media
The media over which the information between two computer systems is sent, called transmission media. Transmission media comes in two forms.
- Guided Media
All communication wires/cables are guided media, such as UTP, coaxial cables, and fiber Optics. In this media, the sender and receiver are directly connected and the information is send (guided) through it.
- Unguided Media
Wireless or open-air space is said to be unguided media, because there is no connectivity between the sender and receiver. Information is spread over the air, and anyone including the actual recipient may collect the information.
Channel Capacity
The speed of transmission of information is said to be the channel capacity. We count it as data rate in digital world. It depends on numerous factors such as:
- Bandwidth: The physical limitation of underlying media.
- Error-rate: Incorrect reception of information because of noise.
- Encoding: The number of levels used for signaling.
Multiplexing
Multiplexing is a technique to mix and send multiple data streams over a single medium. This technique requires system hardware called multiplexer (MUX) for multiplexing the streams and sending them on a medium, and de-multiplexer (DMUX) which takes information from the medium and distributes to different destinations.
Switching
Switching is a mechanism by which data/information sent from source towards destination which are not directly connected. Networks have interconnecting devices, which receives data from directly connected sources, stores data, analyze it and then forwards to the next interconnecting device closest to the destination.
Switching can be categorized as:
Digital Transmission in Computer Network
Data or information can be stored in two ways, analog and digital. For a computer to use the data, it must be in discrete digital form.Similar to data, signals can also be in analog and digital form. To transmit data digitally, it needs to be first converted to digital form.
Digital-to-Digital Conversion
This section explains how to convert digital data into digital signals. It can be done in two ways, line coding and block coding. For all communications, line coding is necessary whereas block coding is optional.
Line Coding
The process for converting digital data into digital signal is said to be Line Coding. Digital data is found in binary format. It is represented (stored) internally as series of 1s and 0s.
Digital signal is denoted by discreet signal, which represents digital data.There are three types of line coding schemes available:
- Uni-polar Encoding
Unipolar encoding schemes use single voltage level to represent data. In this case, to represent binary 1, high voltage is transmitted and to represent 0, no voltage is transmitted. It is also called Unipolar-Non-return-to-zero, because there is no rest condition i.e. it either represents 1 or 0.
- Polar Encoding
Polar encoding scheme uses multiple voltage levels to represent binary values. Polar encodings is available in four types:
Polar Non-Return to Zero (Polar NRZ)
It uses two different voltage levels to represent binary values. Generally, positive voltage represents 1 and negative value represents 0. It is also NRZ because there is no rest condition.
NRZ scheme has two variants: NRZ-L and NRZ-I.
NRZ-L changes voltage level at when a different bit is encountered whereas NRZ-I changes voltage when a 1 is encountered.
- Return to Zero (RZ)
Problem with NRZ is that the receiver cannot conclude when a bit ended and when the next bit is started, in case when sender and receiver’s clock are not synchronized.
RZ uses three voltage levels, positive voltage to represent 1, negative voltage to represent 0 and zero voltage for none. Signals change during bits not between bits.
- Manchester
This encoding scheme is a combination of RZ and NRZ-L. Bit time is divided into two halves. It transits in the middle of the bit and changes phase when a different bit is encountered.
- Differential Manchester
This encoding scheme is a combination of RZ and NRZ-I. It also transit at the middle of the bit but changes phase only when 1 is encountered.
- Bipolar Encoding
Bipolar encoding uses three voltage levels, positive, negative and zero. Zero voltage represents binary 0 and bit 1 is represented by altering positive and negative voltages.
Block Coding
To ensure accuracy of the received data frame redundant bits are used. For example, in even-parity, one parity bit is added to make the count of 1s in the frame even. This way the original number of bits is increased. It is called Block Coding.
Block coding is represented by slash notation, mB/nB. Means, m-bit block is substituted with n-bit block where n > m. Block coding involves three steps:
- Division,
- Substitution
After block coding is done, it is line coded for transmission.
Analog-to-Digital Conversion
Microphones create analog voice and camera creates analog videos, which are treated is analog data. To transmit this analog data over digital signals, we need analog to digital conversion.
Analog data is a continuous stream of data in the wave form whereas digital data is discrete. To convert analog wave into digital data, we use Pulse Code Modulation (PCM).
PCM is one of the most commonly used method to convert analog data into digital form. It involves three steps:
- Sampling
- Quantization
- Sampling
The analog signal is sampled every T interval. Most important factor in sampling is the rate at which analog signal is sampled. According to Nyquist Theorem, the sampling rate must be at least two times of the highest frequency of the signal.
- Quantization
Sampling yields discrete form of continuous analog signal. Every discrete pattern shows the amplitude of the analog signal at that instance. The quantization is done between the maximum amplitude value and the minimum amplitude value. Quantization is approximation of the instantaneous analog value.
- Encoding
In encoding, each approximated value is then converted into binary format.
Transmission Modes
The transmission mode decides how data is transmitted between two computers.The binary data in the form of 1s and 0s can be sent in two different modes: Parallel and Serial.
- Parallel Transmission
The binary bits are organized in-to groups of fixed length. Both sender and receiver are connected in parallel with the equal number of data lines. Both computers distinguish between high order and low order data lines. The sender sends all the bits at once on all lines. Because the data lines are equal to the number of bits in a group or data frame, a complete group of bits (data frame) is sent in one go. Advantage of Parallel transmission is high speed and disadvantage is the cost of wires, as it is equal to the number of bits sent in parallel.
- Serial Transmission
In serial transmission, bits are sent one after another in a queue manner. Serial transmission requires only one communication channel.
Serial transmission can be either asynchronous or synchronous.
- Asynchronous Serial Transmission
It is named so because there’is no importance of timing. Data-bits have specific pattern and they help receiver recognize the start and end data bits.For example, a 0 is prefixed on every data byte and one or more 1s are added at the end.
Two continuous data-frames (bytes) may have a gap between them.
- Synchronous Serial Transmission
Timing in synchronous transmission has importance as there is no mechanism followed to recognize start and end data bits.There is no pattern or prefix/suffix method. Data bits are sent in burst mode without maintaining gap between bytes (8-bits). Single burst of data bits may contain a number of bytes. Therefore, timing becomes very important.
It is up to the receiver to recognize and separate bits into bytes.The advantage of synchronous transmission is high speed, and it has no overhead of extra header and footer bits as in asynchronous transmission.
Analog Transmission
To send the digital data over an analog media, it needs to be converted into analog signal. There can be two cases according to data formatting.
Bandpass: The filters are used to filter and pass frequencies of interest. A bandpass is a band of frequencies which can pass the filter.
Low-pass: Low-pass is a filter that passes low frequencies signals.
When digital data is converted into a bandpass analog signal, it is called digital-to-analog conversion. When low-pass analog signal is converted into bandpass analog signal, it is called analog-to-analog conversion.
Digital-to-Analog Conversion
When data from one computer is sent to another via some analog carrier, it is first converted into analog signals. Analog signals are modified to reflect digital data.
An analog signal is characterized by its amplitude, frequency, and phase. There are three kinds of digital-to-analog conversions:
- Amplitude Shift Keying
In this conversion technique, the amplitude of analog carrier signal is modified to reflect binary data.
When binary data represents digit 1, the amplitude is held; otherwise it is set to 0. Both frequency and phase remain same as in the original carrier signal.
- Frequency Shift Keying
In this conversion technique, the frequency of the analog carrier signal is modified to reflect binary data.
This technique uses two frequencies, f1 and f2. One of them, for example f1, is chosen to represent binary digit 1 and the other one is used to represent binary digit 0. Both amplitude and phase of the carrier wave are kept intact.
- Phase Shift Keying
In this conversion scheme, the phase of the original carrier signal is altered to reflect the binary data.
When a new binary symbol is encountered, the phase of the signal is altered. Amplitude and frequency of the original carrier signal is kept intact.
- Quadrature Phase Shift Keying
QPSK alters the phase to reflect two binary digits at once. This is done in two different phases. The main stream of binary data is divided equally into two sub-streams. The serial data is converted in to parallel in both sub-streams and then each stream is converted to digital signal using NRZ technique. Later, both the digital signals are merged together.
Analog-to-Analog Conversion
Analog signals are modified to represent analog data. This conversion is also known as Analog Modulation. Analog modulation is required when bandpass is used. Analog to analog conversion can be done in three ways:
- Amplitude Modulation
In this modulation, the amplitude of the carrier signal is modified to reflect the analog data.
Amplitude modulation is implemented by means of a multiplier. The amplitude of modulating signal (analog data) is multiplied by the amplitude of carrier frequency, which then reflects analog data.
The frequency and phase of carrier signal remain unchanged.
- Frequency Modulation
In this modulation technique, the frequency of the carrier signal is modified to reflect the change in the voltage levels of the modulating signal (analog data).
The amplitude and phase of the carrier signal are not altered.
- Phase Modulation
In the modulation technique, the phase of carrier signal is modulated in order to reflect the change in voltage (amplitude) of analog data signal.
Phase modulation is practically similar to Frequency Modulation, but in Phase modulation frequency of the carrier signal is not increased. Frequency of carrier is signal is changed (made dense and sparse) to reflect voltage change in the amplitude of modulating signal.
Transmission Media in Computer Network
The transmission media is nothing but the physical media over which communication takes place in computer networks.
Magnetic Media
One of the most convenient way to transfer data from one computer to another, even before the birth of networking, was to save it on some storage media and transfer physical from one station to another. Though it may seem old-fashion way in today’s world of high speed internet, but when the size of data is huge, the magnetic media comes into play.
For example, a bank has to handle and transfer huge data of its customer, which stores a backup of it at some geographically far-away place for security reasons and to keep it from uncertain calamities. If the bank needs to store its huge backup data then its,transfer through internet is not feasible.The WAN links may not support such high speed.Even if they do; the cost too high to afford.
In these cases, data backup is stored onto magnetic tapes or magnetic discs, and then shifted physically at remote places.
Twisted Pair Cable
A twisted pair cable is made of two plastic insulated copper wires twisted together to form a single media. Out of these two wires, only one carries actual signal and another is used for ground reference. The twists between wires are helpful in reducing noise (electro-magnetic interference) and crosstalk.
There are two types of twisted pair cables:
- Shielded Twisted Pair (STP) Cable
- Unshielded Twisted Pair (UTP) Cable
STP cables comes with twisted wire pair covered in metal foil. This makes it more indifferent to noise and crosstalk.
UTP has seven categories, each suitable for specific use. In computer networks, Cat-5, Cat-5e, and Cat-6 cables are mostly used. UTP cables are connected by RJ45 connectors.
Coaxial Cable
Coaxial cable has two wires of copper. The core wire lies in the center and it is made of solid conductor. The core is enclosed in an insulating sheath.The second wire is wrapped around over the sheath and that too in turn encased by insulator sheath. This all is covered by plastic cover.
Because of its structure, the coax cable is capable of carrying high frequency signals than that of twisted pair cable. The wrapped structure provides it a good shield against noise and cross talk. Coaxial cables provide high bandwidth rates of up to 450 mbps.
There are three categories of coax cables namely, RG-59 (Cable TV), RG-58 (Thin Ethernet), and RG-11 (Thick Ethernet). RG stands for Radio Government.
Cables are connected using BNC connector and BNC-T. BNC terminator is used to terminate the wire at the far ends.
Power Lines
Power Line communication (PLC) is Layer-1 (Physical Layer) technology which uses power cables to transmit data signals.In PLC, modulated data is sent over the cables. The receiver on the other end de-modulates and interprets the data.
Because power lines are widely deployed, PLC can make all powered devices controlled and monitored. PLC works in half-duplex.
There are two types of PLC:
Narrow band PLC
Broad band PLC
Narrow band PLC provides lower data rates up to 100s of kbps, as they work at lower frequencies (3-5000 kHz). They can be spread over several kilometers.
Broadband PLC provides higher data rates up to 100s of Mbps and works at higher frequencies (1.8 – 250 MHz). They cannot be as much extended as Narrowband PLC.
Fiber Optics
Fiber Optic works on the properties of light. When light ray hits at critical angle it tends to refracts at 90 degree. This property has been used in fiber optic. The core of fiber optic cable is made of high-quality glass or plastic. From one end of it light is emitted, it travels through it and at the other end light detector detects light stream and converts it to electric data.
Fiber Optic provides the highest mode of speed. It comes in two modes, one is single mode fiber and second is multimode fiber. Single mode fiber can carry a single ray of light whereas multimode is capable of carrying multiple beams of light.
Fiber Optic also comes in unidirectional and bidirectional capabilities. To connect and access fiber optic special type of connectors are used. These can be Subscriber Channel (SC), Straight Tip (ST), or MT-RJ.
Wireless Transmission in Computer Network
Wireless transmission is a form of unguided media. Wireless communication involves no physical link established between two or more devices, communicating wirelessly. Wireless signals are spread over in the air and are received and interpreted by appropriate antennas.
When an antenna is attached to electrical circuit of a computer or wireless device, it converts the digital data into wireless signals and spread all over within its frequency range. The receptor on the other end receives these signals and converts them back to digital data.
A little part of electromagnetic spectrum can be used for wireless transmission.
Radio Transmission
Radio frequency is easier to generate and because of its large wavelength it can penetrate through walls and structures alike.Radio waves can have wavelength from 1 mm – 100,000 km and have frequency ranging from 3 Hz (Extremely Low Frequency) to 300 GHz (Extremely High Frequency). Radio frequencies are sub-divided into six bands.
Radio waves at lower frequencies can travel through walls whereas higher RF can travel in straight line and bounce back. The power of low frequency waves decreases sharply as they cover long distance. High frequency radio waves have more power.
Lower frequencies such as VLF, LF, MF bands can travel on the ground up to 1000 kilometers, over the earth’s surface.
Radio waves of high frequencies are prone to be absorbed by rain and other obstacles. They use Ionosphere of earth atmosphere. High frequency radio waves such as HF and VHF bands are spread upwards. When they reach Ionosphere, they are refracted back to the earth.
Microwave Transmission
Electromagnetic waves above 100 MHz tend to travel in a straight line and signals over them can be sent by beaming those waves towards one particular station. Because Microwaves travels in straight lines, both sender and receiver must be aligned to be strictly in line-of-sight.
Microwaves can have wavelength ranging from 1 mm – 1 meter and frequency ranging from 300 MHz to 300 GHz.
Microwave antennas concentrate the waves making a beam of it. As shown in picture above, multiple antennas can be aligned to reach farther. Microwaves have higher frequencies and do not penetrate wall like obstacles.
Microwave transmission depends highly upon the weather conditions and the frequency it is using.
Infrared Transmission
Infrared wave lies in between visible light spectrum and microwaves. It has wavelength of 700-nm to 1-mm and frequency ranges from 300-GHz to 430-THz.
Infrared wave is used for very short range communication purposes such as television and it’s remote. Infrared travels in a straight line hence it is directional by nature. Because of high frequency range, Infrared cannot cross wall-like obstacles.
Light Transmission
Highest most electromagnetic spectrum which can be used for data transmission is light or optical signalling. This is achieved by means of LASER.
Because of frequency light uses, it tends to travel strictly in straight line.Hence the sender and receiver must be in the line-of-sight. Because laser transmission is unidirectional, at both ends of communication the laser and the photo-detector needs to be installed. Laser beam is generally 1mm wide hence it is a work of precision to align two far receptors each pointing to lasers source.
Laser works as Tx (transmitter) and photo-detectors works as Rx (receiver).
Lasers cannot penetrate obstacles such as walls, rain, and thick fog. Additionally, laser beam is distorted by wind, atmosphere temperature, or variation in temperature in the path.
Laser is safe for data transmission as it is very difficult to tap 1mm wide laser without interrupting the communication channel.
Multiplexing in Computer Network
Multiplexing is a technique by which different analog and digital streams of transmission can be simultaneously processed over a shared link. Multiplexing divides the high capacity medium into low capacity logical medium which is then shared by different streams.
Communication is possible over the air (radio frequency), using a physical media (cable), and light (optical fiber). All mediums are capable of multiplexing.
When multiple senders try to send over a single medium, a device called Multiplexer divides the physical channel and allocates one to each. On the other end of communication, a De-multiplexer receives data from a single medium, identifies each, and sends to different receivers.
Frequency Division Multiplexing
When the carrier is frequency, FDM is used. FDM is an analog technology. FDM divides the spectrum or carrier bandwidth in logical channels and allocates one user to each channel. Each user can use the channel frequency independently and has exclusive access of it. All channels are divided in such a way that they do not overlap with each other. Channels are separated by guard bands. Guard band is a frequency which is not used by either channel.
Time Division Multiplexing
TDM is applied primarily on digital signals but can be applied on analogy signals as well. In TDM the shared channel is divided among its user by means of time slot. Each user can transmit data within the provided time slot only. Digital signals are divided in frames, equivalent to time slot i.e. frame of an optimal size which can be transmitted in given time slot.
TDM works in synchronized mode. Both ends, i.e. Multiplexer and De-multiplexer are timely synchronized and both switch to next channel simultaneously.
When channel A transmits its frame at one end,the De-multiplexer provides media to channel A on the other end. As soon as the channel A’s time slot expires, this side switches to channel B. On the other end, the De-multiplexer works in a synchronized manner and provides media to channel B. Signals from different channels travel the path in interleaved manner.
Wavelength Division Multiplexing
Light has different wavelength (colors). In fiber optic mode, multiple optical carrier signals are multiplexed into an optical fiber by using different wavelengths. This is an analog multiplexing technique and is done conceptually in the same manner as FDM but uses light as signals.
Further, on each wavelength time division multiplexing can be incorporated to accommodate more data signals.
Code Division Multiplexing
Multiple data signals can be transmitted over a single frequency by using Code Division Multiplexing. FDM divides the frequency in smaller channels but CDM allows its users to full bandwidth and transmit signals all the time using a unique code. CDM uses orthogonal codes to spread signals.
Each station is assigned with a unique code, called chip. Signals travel with these codes independently, inside the whole bandwidth.The receiver knows in advance the chip code signal it has to receive.
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Multiplexing is a technique by which different analog and digital streams of transmission can be simultaneously processed over a shared link. Multiplexing divides the high capacity medium into low capacity logical medium which is then shared by different streams.
Communication is possible over the air (radio frequency), using a physical media (cable), and light (optical fiber). All mediums are capable of multiplexing.
When multiple senders try to send over a single medium, a device called Multiplexer divides the physical channel and allocates one to each. On the other end of communication, a De-multiplexer receives data from a single medium, identifies each, and sends to different receivers.
Frequency Division Multiplexing
When the carrier is frequency, FDM is used. FDM is an analog technology. FDM divides the spectrum or carrier bandwidth in logical channels and allocates one user to each channel. Each user can use the channel frequency independently and has exclusive access of it. All channels are divided in such a way that they do not overlap with each other. Channels are separated by guard bands. Guard band is a frequency which is not used by either channel.
Time Division Multiplexing
TDM is applied primarily on digital signals but can be applied on analog signals as well. In TDM the shared channel is divided among its user by means of time slot. Each user can transmit data within the provided time slot only. Digital signals are divided in frames, equivalent to time slot i.e. frame of an optimal size which can be transmitted in given time slot.
TDM works in synchronized mode. Both ends, i.e. Multiplexer and De-multiplexer are timely synchronized and both switch to next channel simultaneously.
When channel A transmits its frame at one end,the De-multiplexer provides media to channel A on the other end.As soon as the channel A’s time slot expires, this side switches to channel B. On the other end, the De-multiplexer works in a synchronized manner and provides media to channel B. Signals from different channels travel the path in interleaved manner.
Wavelength Division Multiplexing
Light has different wavelength (colors). In fiber optic mode, multiple optical carrier signals are multiplexed into an optical fiber by using different wavelengths. This is an analog multiplexing technique and is done conceptually in the same manner as FDM but uses light as signals.
Further, on each wavelength time division multiplexing can be incorporated to accommodate more data signals.
Code Division Multiplexing
Multiple data signals can be transmitted over a single frequency by using Code Division Multiplexing. FDM divides the frequency in smaller channels but CDM allows its users to full bandwidth and transmit signals all the time using a unique code. CDM uses orthogonal codes to spread signals.
Each station is assigned with a unique code, called chip. Signals travel with these codes independently, inside the whole bandwidth.The receiver knows in advance the chip code signal it has to receive.
Network Switching
Switching is process to forward packets coming in from one port to a port leading towards the destination. When data comes on a port it is called ingress, and when data leaves a port or goes out it is called egress. A communication system may include number of switches and nodes. At broad level, switching can be divided into two major categories:
- Connectionless:The data is forwarded on behalf of forwarding tables. No previous handshaking is required and acknowledgements are optional.
- Connection Oriented: Before switching data to be forwarded to destination, there is a need to pre-establish circuit along the path between both endpoints. Data is then forwarded on that circuit. After the transfer is completed, circuits can be kept for future use or can be turned down immediately.
Circuit Switching
When two nodes communicate with each other over a dedicated communication path, it is called circuit switching. There ‘is a need of pre-specified route from which data will travels and no other data is permitted. In circuit switching, to transfer the data, circuit must be established so that the data transfer can take place.
Circuits can be permanent or temporary. Applications which use circuit switching may have to go through three phases:
- Establish a circuit
- Transfer the data
- Disconnect the circuit
Circuit switching was designed for voice applications. Telephone is the best suitable example of circuit switching. Before a user can make a call, a virtual path between caller and callee is established over the network.
Message Switching
This technique was somewhere in middle of circuit switching and packet switching. In message switching, the whole message is treated as a data unit and is switching / transferred in its entirety.
A switch working on message switching, first receives the whole message and buffers it until there are resources available to transfer it to the next hop. If the next hop is not having enough resource to accommodate large size message, the message is stored and switch waits.
This technique was considered substitute to circuit switching. As in circuit switching the whole path is blocked for two entities only. Message switching is replaced by packet switching. Message switching has the following drawbacks:
- Every switch in transit path needs enough storage to accommodate entire message.
- Because of store-and-forward technique and waits included until resources are available, message switching is very slow.
- Message switching was not a solution for streaming media and real-time applications.
Packet Switching
Shortcomings of message switching gave birth to an idea of packet switching. The entire message is broken down into smaller chunks called packets. The switching information is added in the header of each packet and transmitted independently.
It is easier for intermediate networking devices to store small size packets and they do not take much resources either on carrier path or in the internal memory of switches.
Packet switching enhances line efficiency as packets from multiple applications can be multiplexed over the carrier. The internet uses packet switching technique. Packet switching enables the user to differentiate data streams based on priorities. Packets are stored and forwarded according to their priority to provide quality of service.
Data-link Layer Introduction
Data Link Layer is second layer of OSI Layered Model. This layer is one of the most complicated layers and has complex functionalities and liabilities. Data link layer hides the details of underlying hardware and represents itself to upper layer as the medium to communicate.
Data link layer works between two hosts which are directly connected in some sense. This direct connection could be point to point or broadcast. Systems on broadcast network are said to be on same link. The work of data link layer tends to get more complex when it is dealing with multiple hosts on single collision domain.
Data link layer is responsible for converting data stream to signals bit by bit and to send that over the underlying hardware. At the receiving end, Data link layer picks up data from hardware which are in the form of electrical signals, assembles them in a recognizable frame format, and hands over to upper layer.
Data link layer has two sub-layers:
- Logical Link Control:It deals with protocols, flow-control, and error control
- Media Access Control:It deals with actual control of media
Functionality of Data-link Layer
Data link layer does many tasks on behalf of upper layer. These are:
- Framing
Data-link layer takes packets from Network Layer and encapsulates them into Frames. Then, it sends each frame bit-by-bit on the hardware. At receiver’ end, data link layer picks up signals from hardware and assembles them into frames.
- Addressing
Data-link layer provides layer-2 hardware addressing mechanism. Hardware address is assumed to be unique on the link. It is encoded into hardware at the time of manufacturing.
- Synchronization
When data frames are sent on the link, both machines must be synchronized in order to transfer to take place.
- Error Control
Sometimes signals may have encountered problem in transition and the bits are flipped. These errors are detected and attempted to recover actual data bits. It also provides error reporting mechanism to the sender.
- Flow Control
Stations on same link may have different speed or capacity. Data-link layer ensures flow control that enables both machine to exchange data on same speed.
- Multi-Access
When host on the shared link tries to transfer the data, it has a high probability of collision. Data-link layer provides mechanism such as CSMA/CD to equip capability of accessing a shared media among multiple Systems.
Error Detection & Correction
There are many reasons such as noise, cross-talk etc., which may help data to get corrupted during transmission. The upper layers work on some generalized view of network architecture and are not aware of actual hardware data processing.Hence, the upper layers expect error-free transmission between the systems. Most of the applications would not function expectedly if they receive erroneous data. Applications such as voice and video may not be that affected and with some errors they may still function well.
Data-link layer uses some error control mechanism to ensure that frames (data bit streams) are transmitted with certain level of accuracy. But to understand how errors is controlled, it is essential to know what types of errors may occur.
Types of Errors
There may be three types of errors:
- Single bit error
In a frame, there is only one bit, anywhere though, which is corrupt.
- Multiple bits error
Frame is received with more than one bits in corrupted state.
- Burst error
Frame contains more than1 consecutive bits corrupted.
Error control mechanism may involve two possible ways:
- Error detection
- Error correction
Error Detection
Errors in the received frames are detected by means of Parity Check and Cyclic Redundancy Check (CRC). In both cases, few extra bits are sent along with actual data to confirm that bits received at other end are same as they were sent. If the counter-check at receiver’ end fails, the bits are considered corrupted.
- Parity Check
One extra bit is sent along with the original bits to make number of 1s either even in case of even parity, or odd in case of odd parity.
The sender while creating a frame counts the number of 1s in it. For example, if even parity is used and number of 1s is even then one bit with value 0 is added. This way number of 1s remains even.If the number of 1s is odd, to make it even a bit with value 1 is added.
The receiver simply counts the number of 1s in a frame. If the count of 1s is even and even parity is used, the frame is considered to be not-corrupted and is accepted. If the count of 1s is odd and odd parity is used, the frame is still not corrupted.
If a single bit flips in transit, the receiver can detect it by counting the number of 1s. But when more than one bits are erro neous, then it is very hard for the receiver to detect the error.
- Cyclic Redundancy Check (CRC)
CRC is a different approach to detect if the received frame contains valid data. This technique involves binary division of the data bits being sent. The divisor is generated using polynomials. The sender performs a division operation on the bits being sent and calculates the remainder. Before sending the actual bits, the sender adds the remainder at the end of the actual bits. Actual data bits plus the remainder is called a codeword. The sender transmits data bits as codewords.
At the other end, the receiver performs division operation on codewords using the same CRC divisor. If the remainder contains all zeros the data bits are accepted, otherwise it is considered as there some data corruption occurred in transit.
Error Correction
In the digital world, error correction can be done in two ways:
- Backward Error CorrectionWhen the receiver detects an error in the data received, it requests back the sender to retransmit the data unit.
- Forward Error CorrectionWhen the receiver detects some error in the data received, it executes error-correcting code, which helps it to auto-recover and to correct some kinds of errors.
The first one, Backward Error Correction, is simple and can only be efficiently used where retransmitting is not expensive. For example, fiber optics. But in case of wireless transmission retransmitting may cost too much. In the latter case, Forward Error Correction is used.
To correct the error in data frame, the receiver must know exactly which bit in the frame is corrupted. To locate the bit in error, redundant bits are used as parity bits for error detection. For example, we take ASCII words (7 bits data), then there could be 8 kind of information we need: first seven bits to tell us which bit is error and one more bit to tell that there is no error.
For m data bits, r redundant bits are used. r bits can provide 2r combinations of information. In m+r bit codeword, there is possibility that the r bits themselves may get corrupted. So the number of r bits used must inform about m+r bit locations plus no-error information, i.e. m+r+1.
Data-link Control & Protocols
Data-link layer is responsible for implementation of point-to-point flow and error control mechanism.
Flow Control
When a data frame (Layer-2 data) is sent from one host to another over a single medium, it is required that the sender and receiver should work at the same speed. That is, sender sends at a speed on which the receiver can process and accept the data. What if the speed (hardware/software) of the sender or receiver differs? If sender is sending too fast the receiver may be overloaded, (swamped) and data may be lost.
Two types of mechanisms can be deployed to control the flow:
- Stop and Wait
This flow control mechanism forces the sender after transmitting a data frame to stop and wait until the acknowledgement of the data-frame sent is received.
- Sliding Window
In this flow control mechanism, both sender and receiver agree on the number of data-frames after which the acknowledgement should be sent. As we learnt, stop and wait flow control mechanism wastes resources, this protocol tries to make use of underlying resources as much as possible.
Error Control
When data-frame is transmitted, there is a probability that data-frame may be lost in the transit or it is received corrupted. In both cases, the receiver does not receive the correct data-frame and sender does not know anything about any loss.In such case, both sender and receiver are equipped with some protocols which helps them to detect transit errors such as loss of data-frame. Hence, either the sender retransmits the data-frame or the receiver may request to resend the previous data-frame.
Requirements for error control mechanism:
- Error detection– The sender and receiver, either both or any, must ascertain that there is some error in the transit.
- Positive ACK– When the receiver receives a correct frame, it should acknowledge it.
- Negative ACK– When the receiver receives a damaged frame or a duplicate frame, it sends a NACK back to the sender and the sender must retransmit the correct frame.
- Retransmission: The sender maintains a clock and sets a timeout period. If an acknowledgement of a data-frame previously transmitted does not arrive before the timeout the sender retransmits the frame, thinking that the frame or it’s acknowledgement is lost in transit.
There are three types of techniques available which Data-link layer may deploy to control the errors by Automatic Repeat Requests (ARQ):
- Stop-and-wait ARQ
The following transition may occur in Stop-and-Wait ARQ:
- The sender maintains a timeout counter.
- When a frame is sent, the sender starts the timeout counter.
- If acknowledgement of frame comes in time, the sender transmits the next frame in queue.
- If acknowledgement does not come in time, the sender assumes that either the frame or its acknowledgement is lost in transit. Sender retransmits the frame and starts the timeout counter.
- If a negative acknowledgement is received, the sender retransmits the frame.
- Go-Back-N ARQ
Stop and wait ARQ mechanism does not utilize the resources at their best.When the acknowledgement is received, the sender sits idle and does nothing. In Go-Back-N ARQ method, both sender and receiver maintain a window.
The sending-window size enables the sender to send multiple frames without receiving the acknowledgement of the previous ones. The receiving-window enables the receiver to receive multiple frames and acknowledge them. The receiver keeps track of incoming frame’s sequence number.
When the sender sends all the frames in window, it checks up to what sequence number it has received positive acknowledgement. If all frames are positively acknowledged, the sender sends next set of frames. If sender finds that it has received NACK or has not receive any ACK for a particular frame, it retransmits all the frames after which it does not receive any positive ACK.
- Selective Repeat ARQ
In Go-back-N ARQ, it is assumed that the receiver does not have any buffer space for its window size and has to process each frame as it comes. This enforces the sender to retransmit all the frames which are not acknowledged.
In Selective-Repeat ARQ, the receiver while keeping track of sequence numbers, buffers the frames in memory and sends NACK for only frame which is missing or damaged.
The sender in this case, sends only packet for which NACK is received.
Network Layer Introduction
Layer-3 in the OSI model is called Network layer. Network layer manages options pertaining to host and network addressing, managing sub-networks, and internetworking.
Network layer takes the responsibility for routing packets from source to destination within or outside a subnet. Two different subnet may have different addressing schemes or non-compatible addressing types. Same with protocols, two different subnet may be operating on different protocols which are not compatible with each other. Network layer has the responsibility to route the packets from source to destination, mapping different addressing schemes and protocols.
Layer-3 Functionalities
Devices which work on Network Layer mainly focus on routing. Routing may include various tasks aimed to achieve a single goal. These can be:
- Addressing devices and networks.
- Populating routing tables or static routes.
- Queuing incoming and outgoing data and then forwarding them according to quality of service constraints set for those packets.
- Internetworking between two different subnets.
- Delivering packets to destination with best efforts.
- Provides connection oriented and connection less mechanism.
Network Layer Features
With its standard functionalities, Layer 3 can provide various features as:
- Quality of service management
- Load balancing and link management
- Security
- Interrelation of different protocols and subnets with different schema.
- Different logical network design over the physical network design.
- L3 VPN and tunnels can be used to provide end to end dedicated connectivity.
Internet protocol is widely respected and deployed Network Layer protocol which helps to communicate end to end devices over the internet. It comes in two flavors. IPv4 which has ruled the world for decades but now is running out of address space. IPv6 is created to replace IPv4 and hopefully mitigates limitations of IPv4 too.
Network Addressing
Layer 3 network addressing is one of the major tasks of Network Layer. Network Addresses are always logical i.e. these are software-based addresses which can be changed by appropriate configurations.
A network address always points to host / node / server or it can represent a whole network. Network address is always configured on network interface card and is generally mapped by system with the MAC address (hardware address or layer-2 address) of the machine for Layer-2 communication.
There are different kinds of network addresses in existence:
- IP
- IPX
- AppleTalk
We are discussing IP here as it is the only one we use in practice these days.
IP addressing provides mechanism to differentiate between hosts and network. Because IP addresses are assigned in hierarchical manner, a host always resides under a specific network. The host which needs to communicate outside its subnet, needs to know destination network address, where the packet/data is to be sent.
Hosts in different subnet need a mechanism to locate each other. This task can be done by DNS. DNS is a server which provides Layer-3 address of remote host mapped with its domain name or FQDN. When a host acquires the Layer-3 Address (IP Address) of the remote host, it forwards all its packet to its gateway. A gateway is a router equipped with all the information which leads to route packets to the destination host.
Routers take help of routing tables, which has the following information:
Method to reach the network
Routers upon receiving a forwarding request, forwards packet to its next hop (adjacent router) towards the destination.
The next router on the path follows the same thing and eventually the data packet reaches its destination.
Network address can be of one of the following:
- Unicast (destined to one host)
- Multicast (destined to group)
- Broadcast (destined to all)
- Anycast (destined to nearest one)
A router never forwards broadcast traffic by default. Multicast traffic uses special treatment as it is most a video stream or audio with highest priority. Anycast is just similar to unicast, except that the packets are delivered to the nearest destination when multiple destinations are available.
Network Layer Routing
When a device has multiple paths to reach a destination, it always selects one path by preferring it over others. This selection process is termed as Routing. Routing is done by special network devices called routers or it can be done by means of software processes. The software based routers have limited functionality and limited scope.
A router is always configured with some default route. A default route tells the router where to forward a packet if there is no route found for specific destination. In case there are multiple path existing to reach the same destination, router can make decision based on the following information:
- Hop Count
- Bandwidth
- Metric
- Prefix-length
- Delay
Routes can be statically configured or dynamically learnt. One route can be configured to be preferred over others.
Unicast routing
Most of the traffic on the internet and intranets known as unicast data or unicast traffic is sent with specified destination. Routing unicast data over the internet is called unicast routing. It is the simplest form of routing because the destination is already known. Hence the router just has to look up the routing table and forward the packet to next hop.
Broadcast routing
By default, the broadcast packets are not routed and forwarded by the routers on any network. Routers create broadcast domains. But it can be configured to forward broadcasts in some special cases. A broadcast message is destined to all network devices.
Broadcast routing can be done in two ways (algorithm):
- A router creates a data packet and then sends it to each host one by one. In this case, the router creates multiple copies of single data packet with different destination addresses. All packets are sent as unicast but because they are sent to all, it simulates as if router is broadcasting.
This method consumes lots of bandwidth and router must destination address of each node.
- Secondly, when router receives a packet that is to be broadcasted, it simply floods those packets out of all interfaces. All routers are configured in the same way.
This method is easy on router’s CPU but may cause the problem of duplicate packets received from peer routers.
Reverse path forwarding is a technique, in which router knows in advance about its predecessor from where it should receive broadcast. This technique is used to detect and discard duplicates.
Multicast Routing
Multicast routing is special case of broadcast routing with significance difference and challenges. In broadcast routing, packets are sent to all nodes even if they do not want it. But in Multicast routing, the data is sent to only nodes which wants to receive the packets.
The router must know that there are nodes, which wish to receive multicast packets (or stream) then only it should forward. Multicast routing works spanning tree protocol to avoid looping.
Multicast routing also uses reverse path Forwarding technique, to detect and discard duplicates and loops.
Anycast Routing
Anycast packet forwarding is a mechanism where multiple hosts can have same logical address. When a packet destined to this logical address is received, it is sent to the host which is nearest in routing topology.
Anycast routing is done with help of DNS server. Whenever an Anycast packet is received it is enquired with DNS to where to send it. DNS provides the IP address which is the nearest IP configured on it.
Unicast Routing Protocols
There are two kinds of routing protocols available to route unicast packets:
Distance Vector Routing Protocol
Distance Vector is simple routing protocol which takes routing decision on the number of hops between source and destination. A route with less number of hops is considered as the best route. Every router advertises its set best routes to other routers. Ultimately, all routers build up their network topology based on the advertisements of their peer routers,
For example, Routing Information Protocol (RIP).
Link State Routing Protocol
Link State protocol is slightly complicated protocol than Distance Vector. It considers the states of links of all the routers in a network. This technique helps routes build a common graph of the entire network. All routers then calculate their best path for routing purposes. For example, Open Shortest Path First (OSPF) and Intermediate System to Intermediate System (ISIS).
Multicast Routing Protocols
Unicast routing protocols use graphs while Multicast routing protocols use trees, i.e. spanning tree to avoid loops. The optimal tree is called shortest path spanning tree.
- DVMRP– Distance Vector Multicast Routing Protocol
- MOSPF– Multicast Open Shortest Path First
- CBT– Core Based Tree
- PIM– Protocol independent Multicast
Protocol Independent Multicast is commonly used now. It has two flavors:
- PIM Dense Mode
This mode uses source-based trees. It is used in dense environment such as LAN.
- PIM Sparse Mode
This mode uses shared trees. It is used in sparse environment such as WAN.
Routing Algorithms
The routing algorithms are as follows:
Flooding
Flooding is simplest method packet forwarding. When a packet is received, the routers send it to all the interfaces except the one on which it was received. This creates too much burden on the network and lots of duplicate packets wandering in the network.
Time to Live (TTL) can be used to avoid infinite looping of packets. There exists another approach for flooding, which is called Selective Flooding to reduce the overhead on the network. In this method, the router does not flood out on all the interfaces, but selective ones.
Shortest Path
Routing decision in networks, are mostly taken on the basis of cost between source and destination. Hop count plays major role here. Shortest path is a technique which uses various algorithms to decide a path with minimum number of hops.
Common shortest path algorithms are:
- Dijkstra’s algorithm
- Bellman Ford algorithm
- Floyd War shall algorithm
Internetworking in Computer Network
In real world scenario, networks under same administration are generally scattered geographically. There may exist requirement of connecting two different networks of same kind as well as of different kinds. Routing between two networks is called internetworking.
Networks can be considered different based on various parameters such as, Protocol, topology, Layer-2 network and addressing scheme.
In internetworking, routers have knowledge of each other’s address and addresses beyond them. They can be statically configured go on different network or they can learn by using internetworking routing protocol.
Routing protocols which are used within an organization or administration are called Interior Gateway Protocols or IGP. RIP, OSPF are examples of IGP. Routing between different organizations or administrations may have Exterior Gateway Protocol, and there is only one EGP i.e. Border Gateway Protocol.
Tunneling
If they are two geographically separate networks, which want to communicate with each other, they may deploy a dedicated line between or they have to pass their data through intermediate networks.
Tunneling is a mechanism by which two or more same networks communicate with each other, by passing intermediate networking complexities. Tunneling is configured at both ends.
When the data enters from one end of Tunnel, it is tagged. This tagged data is then routed inside the intermediate or transit network to reach the other end of Tunnel. When data exists the Tunnel its tag is removed and delivered to the other part of the network.
Both ends seem as if they are directly connected and tagging makes data travel through transit network without any modifications.
Packet Fragmentation
Most Ethernet segments have their maximum transmission unit (MTU) fixed to 1500 bytes. A data packet can have more or less packet length depending upon the application. Devices in the transit path also have their hardware and software capabilities which tell what amount of data that device can handle and what size of packet it can process.
If the data packet size is less than or equal to the size of packet the transit network can handle, it is processed neutrally. If the packet is larger, it is broken into smaller pieces and then forwarded. This is called packet fragmentation. Each fragment contains the same destination and source address and routed through transit path easily. At the receiving end it is assembled again.
If a packet with DF (don’t fragment) bit set to 1 comes to a router which can not handle the packet because of its length, the packet is dropped.
When a packet is received by a router has its MF (more fragments) bit set to 1, the router then knows that it is a fragmented packet and parts of the original packet is on the way.
If packet is fragmented too small, the overhead is increases. If the packet is fragmented too large, intermediate router may not be able to process it and it might get dropped.
Network Layer Protocols
Every computer in a network has an IP address by which it can be uniquely identified and addressed. An IP address is Layer-3 (Network Layer) logical address. This address may change every time a computer restarts. A computer can have one IP at one instance of time and another IP at some different time.
Address Resolution Protocol (ARP)
While communicating, a host needs Layer-2 (MAC) address of the destination machine which belongs to the same broadcast domain or network. A MAC address is physically burnt into the Network Interface Card (NIC) of a machine and it never changes.
On the other hand, IP address on the public domain is rarely changed. If the NIC is changed in case of some fault, the MAC address also changes. This way, for Layer-2 communication to take place, a mapping between the two is required.
To know the MAC address of remote host on a broadcast domain, a computer wishing to initiate communication sends out an ARP broadcast message asking, “Who has this IP address?” Because it is a broadcast, all hosts on the network segment (broadcast domain) receive this packet and process it. ARP packet contains the IP address of destination host, the sending host wishes to talk to. When a host receives an ARP packet destined to it, it replies back with its own MAC address.
Once the host gets destination MAC address, it can communicate with remote host using Layer-2 link protocol. This MAC to IP mapping is saved into ARP cache of both sending and receiving hosts. Next time, if they require to communicate, they can directly refer to their respective ARP cache.
Reverse ARP is a mechanism where host knows the MAC address of remote host but requires to know IP address to communicate.
Internet Control Message Protocol (ICMP)
ICMP is network diagnostic and error reporting protocol. ICMP belongs to IP protocol suite and uses IP as carrier protocol. After constructing ICMP packet, it is encapsulated in IP packet. Because IP itself is a best-effort non-reliable protocol, so is ICMP.
Any feedback about network is sent back to the originating host. If some error in the network occurs, it is reported by means of ICMP. ICMP contains dozens of diagnostic and error reporting messages.
ICMP-echo and ICMP-echo-reply are the most commonly used ICMP messages to check the reachability of end-to-end hosts. When a host receives an ICMP-echo request, it is bound to send back an ICMP-echo-reply. If there is any problem in the transit network, the ICMP will report that problem.
Internet Protocol Version 4 (IPv4)
IPv4 is 32-bit addressing scheme used as TCP/IP host addressing mechanism. IP addressing enables every host on the TCP/IP network to be uniquely identifiable.
IPv4 provides hierarchical addressing scheme which enables it to divide the network into sub-networks, each with well-defined number of hosts. IP addresses are divided into many categories:
- Class A– it uses first octet for network addresses and last three octets for host addressing
- Class B– it uses first two octets for network addresses and last two for host addressing
- Class C– it uses first three octets for network addresses and last one for host addressing
- Class D– it provides flat IP addressing scheme in contrast to hierarchical structure for above three.
- Class E– It is used as experimental.
IPv4 also has well-defined address spaces to be used as private addresses (not routable on internet), and public addresses (provided by ISPs and are routable on internet).
Though IP is not reliable one; it provides ‘Best-Effort-Delivery’ mechanism.
Internet Protocol Version 6 (IPv6)
Exhaustion of IPv4 addresses gave birth to a next generation Internet Protocol version 6. IPv6 addresses its nodes with 128-bit wide address providing plenty of address space for future to be used on entire planet or beyond.
IPv6 has introduced Anycast addressing but has removed the concept of broadcasting. IPv6 enables devices to self-acquire an IPv6 address and communicate within that subnet. This auto-configuration removes the dependability of Dynamic Host Configuration Protocol (DHCP) servers. This way, even if the DHCP server on that subnet is down, the hosts can communicate with each other.
IPv6 provides new feature of IPv6 mobility. Mobile IPv6 equipped machines can roam around without the need of changing their IP addresses.
IPv6 is still in transition phase and is expected to replace IPv4 completely in coming years. At present, there are few networks which are running on IPv6. There are some transition mechanisms available for IPv6 enabled networks to speak and roam around different networks easily on IPv4. These are:
- Dual stack implementation
- Tunneling
- NAT-PT
Transport Layer Introduction
Next Layer in OSI Model is recognized as Transport Layer (Layer-4). All modules and procedures pertaining to transportation of data or data stream are categorized into this layer. As all other layers, this layer communicates with its peer Transport layer of the remote host.
Transport layer offers peer-to-peer and end-to-end connection between two processes on remote hosts. Transport layer takes data from upper layer (i.e. Application layer) and then breaks it into smaller size segments, numbers each byte, and hands over to lower layer (Network Layer) for delivery.
Functions
- This Layer is the first one which breaks the information data, supplied by Application layer in to smaller units called segments. It numbers every byte in the segment and maintains their accounting.
- This layer ensures that data must be received in the same sequence in which it was sent.
- This layer provides end-to-end delivery of data between hosts which may or may not belong to the same subnet.
- All server processes intend to communicate over the network are equipped with well-known Transport Service Access Points (TSAPs) also known as port numbers.
End-to-End Communication
A process on one host identifies its peer host on remote network by means of TSAPs, also known as Port numbers. TSAPs are very well defined and a process which is trying to communicate with its peer knows this in advance.
For example, when a DHCP client wants to communicate with remote DHCP server, it always requests on port number 67. When a DNS client wants to communicate with remote DNS server, it always requests on port number 53 (UDP).
The two main Transport layer protocols are:
- Transmission Control Protocol
It provides reliable communication between two hosts.
- User Datagram Protocol
It provides unreliable communication between two hosts.
Transmission Control Protocol
The transmission Control Protocol (TCP) is one of the most important protocols of Internet Protocols suite. It is most widely used protocol for data transmission in communication network such as internet.
Features
- TCP is reliable protocol. That is, the receiver always sends either positive or negative acknowledgement about the data packet to the sender, so that the sender always has bright clue about whether the data packet is reached the destination or it needs to resend it.
- TCP ensures that the data reaches intended destination in the same order it was sent.
- TCP is connection oriented. TCP requires that connection between two remote points be established before sending actual data.
- TCP provides error-checking and recovery mechanism.
- TCP provides end-to-end communication.
- TCP provides flow control and quality of service.
- TCP operates in Client/Server point-to-point mode.
- TCP provides full duplex server, i.e. it can perform roles of both receiver and sender.
Header
The length of TCP header is minimum 20 bytes long and maximum 60 bytes.
- Source Port (16-bits)– It identifies source port of the application process on the sending device.
- Destination Port (16-bits)– It identifies destination port of the application process on the receiving device.
- Sequence Number (32-bits)– Sequence number of data bytes of a segment in a session.
- Acknowledgement Number (32-bits)– When ACK flag is set, this number contains the next sequence number of the data byte expected and works as acknowledgement of the previous data received.
- Data Offset (4-bits)– This field implies both, the size of TCP header (32-bit words) and the offset of data in current packet in the whole TCP segment.
- Reserved (3-bits)– Reserved for future use and all are set zero by default.
- Flags (1-bit each)
- NS– Nonce Sum bit is used by Explicit Congestion Notification signaling process.
- CWR– When a host receives packet with ECE bit set, it sets Congestion Windows Reduced to acknowledge that ECE received.
- ECE-It has two meanings:
- If SYN bit is clear to 0, then ECE means that the IP packet has its CE (congestion experience) bit set.
- If SYN bit is set to 1, ECE means that the device is ECT capable.
- URG– It indicates that Urgent Pointer field has significant data and should be processed.
- ACK– It indicates that Acknowledgement field has significance. If ACK is cleared to 0, it indicates that packet does not contain any acknowledgement.
- PSH– When set, it is a request to the receiving station to PUSH data (as soon as it comes) to the receiving application without buffering it.
- RST– Reset flag has the following features:
- It is used to refuse an incoming connection.
- It is used to reject a segment.
- It is used to restart a connection.
- SYN– This flag is used to set up a connection between hosts.
- FIN– This flag is used to release a connection and no more data is exchanged thereafter. Because packets with SYN and FIN flags have sequence numbers, they are processed in correct order.
- Windows Size– This field is used for flow control between two stations and indicates the amount of buffer (in bytes) the receiver has allocated for a segment, i.e. how much data is the receiver expecting.
- Checksum– This field contains the checksum of Header, Data and Pseudo Headers.
- Urgent Pointer– It points to the urgent data byte if URG flag is set to 1.
- Options– It facilitates additional options which are not covered by the regular header. Option field is always described in 32-bit words. If this field contains data less than 32-bit, padding is used to cover the remaining bits to reach 32-bit boundary.
Addressing
TCP communication between two remote hosts is done by means of port numbers (TSAPs). Ports numbers can range from 0 – 65535 which are divided as:
- System Ports (0 – 1023)
- User Ports (1024 – 49151)
- Private/Dynamic Ports (49152 – 65535)
Connection Management
TCP communication works in Server/Client model. The client initiates the connection and the server either accepts or rejects it. Three-way handshaking is used for connection management.
Establishment
Client initiates the connection and sends the segment with a Sequence number. Server acknowledges it back with its own Sequence number and ACK of client’s segment which is one more than client’s Sequence number. Client after receiving ACK of its segment sends an acknowledgement of Server’s response.
Release
Either of server and client can send TCP segment with FIN flag set to 1. When the receiving end responds it back by ACKnowledging FIN, that direction of TCP communication is closed and connection is released.
Bandwidth Management
TCP uses the concept of window size to accommodate the need of Bandwidth management. Window size tells the sender at the remote end, the number of data byte segments the receiver at this end can receive. TCP uses slow start phase by using window size 1 and increases the window size exponentially after each successful communication.
For example, the client uses windows size 2 and sends 2 bytes of data. When the acknowledgement of this segment received the windows size is doubled to 4 and next sent the segment sent will be 4 data bytes long. When the acknowledgement of 4-byte data segment is received, the client sets windows size to 8 and so on.
If an acknowledgement is missed, i.e. data lost in transit network or it received NACK, then the window size is reduced to half and slow start phase starts again.
Error Control &and Flow Control
TCP uses port numbers to know what application process it needs to handover the data segment. Along with that, it uses sequence numbers to synchronize itself with the remote host. All data segments are sent and received with sequence numbers. The Sender knows which last data segment was received by the Receiver when it gets ACK. The Receiver knows about the last segment sent by the Sender by referring to the sequence number of recently received packet.
If the sequence number of a segment recently received does not match with the sequence number the receiver was expecting, then it is discarded and NACK is sent back. If two segments arrive with the same sequence number, the TCP timestamp value is compared to decide.
Multiplexing
The technique to combine two or more data streams in one session is called Multiplexing. When a TCP client initializes a connection with Server, it always refers to a well-defined port number which indicates the application process. The client itself uses a randomly generated port number from private port number pools.
Using TCP Multiplexing, a client can communicate with a number of different application process in a single session. For example, a client requests a web page which in turn contains different types of data (HTTP, SMTP, FTP etc.) the TCP session timeout is increased and the session is kept open for longer time so that the three-way handshake overhead can be avoided.
This enables the client system to receive multiple connection over single virtual connection. These virtual connections are not good for Servers if the timeout is too long.
Congestion Control
When large amount of data is fed to system which is not capable of handling it, congestion occurs. TCP controls congestion by means of Window mechanism. TCP sets a window size telling the other end how much data segment to send. TCP may use three algorithms for congestion control:
- Additive increase, Multiplicative Decrease
- Slow Start
- Timeout React
Timer Management
TCP uses different types of timer to control and management various tasks:
Keep-alive timer:
- This timer is used to check the integrity and validity of a connection.
- When keep-alive time expires, the host sends a probe to check if the connection still exists.
Retransmission timer:
- This timer maintains stateful session of data sent.
- If the acknowledgement of sent data does not receive within the Retransmission time, the data segment is sent again.
Persist timer:
- TCP session can be paused by either host by sending Window Size 0.
- To resume the session a host needs to send Window Size with some larger value.
- If this segment never reaches the other end, both ends may wait for each other for infinite time.
- When the Persist timer expires, the host re-sends its window size to let the other end know.
- Persist Timer helps avoid deadlocks in communication.
Timed-Wait:
- After releasing a connection, either of the hosts waits for a Timed-Wait time to terminate the connection completely.
- This is in order to make sure that the other end has received the acknowledgement of its connection termination request.
- Timed-out can be a maximum of 240 seconds (4 minutes).
Crash Recovery
TCP is very reliable protocol. It provides sequence number to each of byte sent in segment. It provides the feedback mechanism i.e. when a host receives a packet, it is bound to ACK that packet having the next sequence number expected (if it is not the last segment).
When a TCP Server crashes mid-way communication and re-starts its process it sends TPDU broadcast to all its hosts. The hosts can then send the last data segment which was never unacknowledged and carry onwards.
User Datagram Protocol
The User Datagram Protocol (UDP) is simplest Transport Layer communication protocol available of the TCP/IP protocol suite. It involves minimum amount of communication mechanism. UDP is said to be an unreliable transport protocol but it uses IP services which provides best effort delivery mechanism.
In UDP, the receiver does not generate an acknowledgement of packet received and in turn, the sender does not wait for any acknowledgement of packet sent. This shortcoming makes this protocol unreliable as well as easier on processing.
Requirement of UDP
A question may arise, why do we need an unreliable protocol to transport the data? We deploy UDP where the acknowledgement packets share significant amount of bandwidth along with the actual data. For example, in case of video streaming, thousands of packets are forwarded towards its users. Acknowledging all the packets is troublesome and may contain huge amount of bandwidth wastage. The best delivery mechanism of underlying IP protocol ensures best efforts to deliver its packets, but even if some packets in video streaming get lost, the impact is not calamitous and can be ignored easily. Loss of few packets in video and voice traffic sometimes goes unnoticed.
Features
- UDP is used when acknowledgement of data does not hold any significance.
- UDP is good protocol for data flowing in one direction.
- UDP is simple and suitable for query based communications.
- UDP is not connection oriented.
- UDP does not provide congestion control mechanism.
- UDP does not guarantee ordered delivery of data.
- UDP is stateless.
- UDP is suitable protocol for streaming applications such as VoIP, multimedia streaming.
UDP Header
UDP header is as simple as its function.
UDP header contains four main parameters:
- Source Port– This 16 bits information is used to identify the source port of the packet.
- Destination Port– This 16 bits information, is used identify application level service on destination machine.
- Length– Length field specifies the entire length of UDP packet (including header). It is 16-bits field and minimum value is 8-byte, i.e. the size of UDP header itself.
- Checksum– This field stores the checksum value generated by the sender before sending. IPv4 has this field as optional so when checksum field does not contain any value it is made 0 and all its bits are set to zero.
UDP application
Here are few applications where UDP is used to transmit data:
- Domain Name Services
- Simple Network Management Protocol
- Trivial File Transfer Protocol
- Routing Information Protocol
- Kerberos
Application Layer Introduction
Application layer is the top most layer in OSI and TCP/IP layered model. This layer exists in both layered Models because of its significance, of interacting with user and user applications. This layer is for applications which are involved in communication system.
A user may or may not directly interacts with the applications. Application layer is where the actual communication is initiated and reflects. Because this layer is on the top of the layer stack, it does not serve any other layers. Application layer takes the help of Transport and all layers below it to communicate or transfer its data to the remote host.
When an application layer protocol wants to communicate with its peer application layer protocol on remote host, it hands over the data or information to the Transport layer. The transport layer does the rest with the help of all the layers below it.
There’s an ambiguity in understanding Application Layer and its protocol. Not every user application can be put into Application Layer. except those applications which interact with the communication system. For example, designing software or text-editor cannot be considered as application layer programs.
On the other hand, when we use a Web Browser, which is actually using Hyper Text Transfer Protocol (HTTP) to interact with the network. HTTP is Application Layer protocol.
Another example is File Transfer Protocol, which helps a user to transfer text based or binary files across the network. A user can use this protocol in either GUI based software like FileZilla or Cute FTP and the same user can use FTP in Command Line mode.
Hence, irrespective of which software you use, it is the protocol which is considered at Application Layer used by that software. DNS is a protocol which helps user application protocols such as HTTP to accomplish its work.
Client Server Model
Two remote application processes can communicate mainly in two different fashions:
- Peer-to-peer:Both remote processes are executing at same level and they exchange data using some shared resource.
- Client-Server:One remote process acts as a Client and requests some resource from another application process acting as Server.
In client-server model, any process can act as Server or Client. It is not the type of machine, size of the machine, or its computing power which makes it server; it is the ability of serving request that makes a machine a server.
A system can act as Server and Client simultaneously. That is, one process is acting as Server and another is acting as a client. This may also happen that both client and server processes reside on the same machine.
Communication
Two processes in client-server model can interact in various ways:
- Sockets
- Remote Procedure Calls (RPC)
Sockets
In this paradigm, the process acting as Server opens a socket using a well-known (or known by client) port and waits until some client request comes. The second process acting as a Client also opens a socket but instead of waiting for an incoming request, the client processes ‘requests first’.
When the request is reached to server, it is served. It can either be an information sharing or resource request.
Remote Procedure Call
This is a mechanism where one process interacts with another by means of procedure calls. One process (client) calls the procedure lying on remote host. The process on remote host is said to be Server. Both processes are allocated stubs. This communication happens in the following way:
- The client process calls the client stub. It passes all the parameters pertaining to program local to it.
- All parameters are then packed (marshalled) and a system call is made to send them to other side of the network.
- Kernel sends the data over the network and the other end receives it.
- The remote host passes data to the server stub where it is unmarshalled.
- The parameters are passed to the procedure and the procedure is then executed.
- The result is sent back to the client in the same manner.
Application Protocols in Computer Network
There are several protocols which work for users in Application Layer. Application layer protocols can be broadly divided into two categories:
- Protocols which are used by users.For email for example, eMail.
- Protocols which help and support protocols used by users.For example DNS.
Few of Application layer protocols are described below:
Domain Name System
The Domain Name System (DNS) works on Client Server model. It uses UDP protocol for transport layer communication. DNS uses hierarchical domain based naming scheme. The DNS server is configured with Fully Qualified Domain Names (FQDN) and email addresses mapped with their respective Internet Protocol addresses.
A DNS server is requested with FQDN and it responds back with the IP address mapped with it. DNS uses UDP port 53.
Simple Mail Transfer Protocol
The Simple Mail Transfer Protocol (SMTP) is used to transfer electronic mail from one user to another. This task is done by means of email client software (User Agents) the user is using. User Agents help the user to type and format the email and store it until internet is available. When an email is submitted to send, the sending process is handled by Message Transfer Agent which is normally comes inbuilt in email client software.
Message Transfer Agent uses SMTP to forward the email to another Message Transfer Agent (Server side). While SMTP is used by end user to only send the emails, the Servers normally use SMTP to send as well as receive emails. SMTP uses TCP port number 25 and 587.
Client software uses Internet Message Access Protocol (IMAP) or POP protocols to receive emails.
File Transfer Protocol
The File Transfer Protocol (FTP) is the most widely used protocol for file transfer over the network. FTP uses TCP/IP for communication and it works on TCP port 21. FTP works on Client/Server Model where a client requests file from Server and server sends requested resource back to the client.
FTP uses out-of-band controlling i.e. FTP uses TCP port 20 for exchanging controlling information and the actual data is sent over TCP port 21.
The client requests the server for a file. When the server receives a request for a file, it opens a TCP connection for the client and transfers the file. After the transfer is complete, the server closes the connection. For a second file, client requests again and the server reopens a new TCP connection.
Post Office Protocol (POP)
The Post Office Protocol version 3 (POP 3) is a simple mail retrieval protocol used by User Agents (client email software) to retrieve mails from mail server.
When a client needs to retrieve mails from server, it opens a connection with the server on TCP port 110. User can then access his mails and download them to the local computer. POP3 works in two modes. The most common mode the delete mode, is to delete the emails from remote server after they are downloaded to local machines. The second mode, the keep mode, does not delete the email from mail server and gives the user an option to access mails later on mail server.
Hyper Text Transfer Protocol (HTTP)
The Hyper Text Transfer Protocol (HTTP) is the foundation of World Wide Web. Hypertext is well organized documentation system which uses hyperlinks to link the pages in the text documents. HTTP works on client server model. When a user wants to access any HTTP page on the internet, the client machine at user end initiates a TCP connection to server on port 80. When the server accepts the client request, the client is authorized to access web pages.
To access the web pages, a client normally uses web browsers, who are responsible for initiating, maintaining, and closing TCP connections. HTTP is a stateless protocol, which means the Server maintains no information about earlier requests by clients.
HTTP versions
- HTTP 1.0 uses non-persistent HTTP. At most one object can be sent over a single TCP connection.
- HTTP 1.1 uses persistent HTTP. In this version, multiple objects can be sent over a single TCP connection.
Network Services
Computer systems and computerized systems help human beings to work efficiently and explore the unthinkable. When these devices are connected together to form a network, the capabilities are enhanced multiple-times. Some basic services computer network can offer are.
Directory Services
These services are mapping between name and its value, which can be variable value or fixed. This software system helps to store the information, organize it, and provides various means of accessing it.
- Accounting
In an organization, a number of users have their user names and passwords mapped to them. Directory Services provide means of storing this information in cryptic form and make available when requested.
- Authentication and Authorization
User credentials are checked to authenticate a user at the time of login and/or periodically. User accounts can be set into hierarchical structure and their access to resources can be controlled using authorization schemes.
- Domain Name Services
DNS is widely used and one of the essential services on which internet works. This system maps IP addresses to domain names, which are easier to remember and recall than IP addresses. Because network operates with the help of IP addresses and humans tend to remember website names, the DNS provides website’s IP address which is mapped to its name from the back-end on the request of a website name from the user.
File Services
File services include sharing and transferring files over the network.
- File Sharing
One of the reasons which gave birth to networking was file sharing. File sharing enables its users to share their data with other users. User can upload the file to a specific server, which is accessible by all intended users. As an alternative, user can make its file shared on its own computer and provides access to intended users.
- File Transfer
This is an activity to copy or move file from one computer to another computer or to multiple computers, with help of underlying network. Network enables its user to locate other users in the network and transfers files.
Communication Services
Electronic mail is a communication method and something a computer user cannot work without. This is the basis of today’s internet features. Email system has one or more email servers. All its users are provided with unique IDs. When a user sends email to other user, it is actually transferred between users with help of email server.
- Social Networking
Recent technologies have made technical life social. The computer savvy peoples, can find other known peoples or friends, can connect with them, and can share thoughts, pictures, and videos.
- Internet Chat
Internet chat provides instant text transfer services between two hosts. Two or more people can communicate with each other using text based Internet Relay Chat services. These days, voice chat and video chat are very common.
- Discussion Boards
Discussion boards provide a mechanism to connect multiple peoples with same interests. It enables the users to put queries, questions, suggestions etc. which can be seen by all other users. Other may respond as well.
- Remote Access
This service enables user to access the data residing on the remote computer. This feature is known as Remote desktop. This can be done via some remote device, e.g. mobile phone or home computer.
Application Services
These are nothing but providing network based services to the users such as web services, database managing, and resource sharing.
- Resource Sharing
To use resources efficiently and economically, network provides a mean to share them. This may include Servers, Printers, and Storage Media etc.
- Databases
This application service is one of the most important services. It stores data and information, processes it, and enables the users to retrieve it efficiently by using queries. Databases help organizations to make decisions based on statistics.
- Web Services
World Wide Web has become the synonym for internet. It is used to connect to the internet, and access files and information services provided by the internet servers.
Part-2
Internet
Internet
Internet is a world-wide global system of interconnected computer networks. Internet uses the standard Internet Protocol (TCP/IP). Every computer in internet is identified by a unique IP address. IP Address is a unique set of numbers (such as 110.22.33.114) which identifies a computer location. A special computer DNS (Domain Name Server) is used to give name to the IP Address so that user can locate a computer by a name. For example, a DNS server will resolve a name https://www.ucidream.com to a particular IP address to uniquely identify the computer on which this website is hosted. Internet is accessible to every user all over the world.
Internet Evolution
The concept of Internet was originated in 1969 and has undergone several technological & Infrastructural changes as :
The origin of Internet devised from the concept of Advanced Research Project Agency Network (ARPANET). ARPANET was developed by United States Department of Defense. Basic purpose of ARPANET was to provide communication among the various bodies of government. Initially, there were only four nodes, formally called Hosts. In 1972, the ARPANET spread over the globe with 23 nodes located at different countries and thus became known as Internet. By the time, with invention of new technologies such as TCP/IP protocols, DNS, WWW, browsers, scripting languages etc., Internet provided a medium to publish and access information over the web.
Extranet
Extranet refers to network within an organization, using internet to connect to the outsiders in controlled manner. It helps to connect businesses with their customers and suppliers and therefore allows working in a collaborative manner.
Extranet vs Intranet
Extranet- Internal network that can be accessed externally. Extranet is extension of company’s Intranet. For limited external communication between customers, suppliers and business partners.
Intranet- Internal network that cannot be accessed externally. Only limited users of a company. Only for communication within a company.
Internet Models
OSI Reference Model
OSI Reference Model- OSI is acronym of Open System Interface. This model is developed by the international organization of Standardization (ISO) and therefore also referred as ISO-OSI Model. The OSI model consists of seven layers. Each layer has a specific function; however, each layer provides services to the layer above.
- Physical Layer- The Physical layer is responsible for this type’s activities. Activating, maintaining and deactivating the physical connection. Defining voltages and data rates needed for transmission. Converting digital bits into electrical signal. Deciding whether the connection is simplex, half duplex or full duplex.
- Data Link Layer- The data link layer performs for these functions. Performs synchronization and error control for the information which is to be transmitted over the physical link. Enables error detection, and adds error detection bits to the data which are to be transmitted.
- Network Layer- These are the functions of Network Layer- To route the signals through various channels to the other end. To act as the network controller by deciding which route data should take. To divide the outgoing messages into packets and to assemble incoming packets into messages for higher levels.
- Transport Layer- The Transport layer performs for these functions. It decides if the data transmission should take place on parallel paths or single path. It performs multiplexing, splitting on the data. It breaks the data groups into smaller units so that they are handled more efficiently by the network layer. The Transport Layer guarantees transmission of data from one end to another end.
- Session Layer- The Session layer performs for these functions. Manages the messages and synchronizes conversations between two different applications. It controls logging on and off, user identification, billing and session management.
- Presentation Layer- The Presentation layer performs for these functions- <=”” ul=”” style=”margin-top: 0px; margin-bottom: 0rem !important; color: rgba(0, 0, 0, 0.87); font-family: Arial, Verdana, Tahoma; font-size: 16px; font-style: normal; font-variant-ligatures: normal; font-variant-caps: normal; font-weight: 400; letter-spacing: normal; orphans: 2; text-align: start; text-indent: 0px; text-transform: none; white-space: normal; widows: 2; word-spacing: 0px; -webkit-text-stroke-width: 0px; text-decoration-thickness: initial; text-decoration-style: initial; text-decoration-color: initial;”>. This layer makes it sure that the information is delivered in such a form that the receiving system will understand and use it.
- Application Layer
The Application layer performs for these functions- It provides different services such as manipulation of information in several ways, retransferring the files of information, distributing the results etc. The functions such as LOGIN or password checking are also performed by the application layer.
TCP/IP Reference Model
TCP/IP model is practical model and is used in the Internet. TCP/IP is acronym of Transmission Control Protocol and Internet Protocol. The TCP/IP model combines the two layers (Physical and Data link layer) into one layer i.e., Host-to-Network layer. The various layers of TCP/IP model:
- Application Layer- This layer is same as that of the OSI model and performs for these functions. It provides different services such as manipulation of information in several ways, retransferring the files of information, distributing the results etc. The functions such as LOGIN or password checking are also performed by the application layer.
Protocols used: TELNET, FTP, SMTP, DN, HTTP, NNTP are the protocols employed in this layer.
- Transport Layer- It does the same functions as that of transport layer in OSI model. Here are the key points regarding transport layer. It uses TCP and UDP protocol for end-to-end transmission. TCP is reliable and connection-oriented protocol. TCP also handles flow control. The UDP is not reliable and a connection less protocol also does not perform flow control.
Protocols used: TCP/IP and UDP protocols are employed in this layer.
- Internet Layer- The function of this layer is to allow the host to insert packets into network and then make them travel independently to the destination. However, the order of receiving the packet can be different from the sequence they were sent.
Protocols used: Internet Protocol (IP) is employed in Internet layer.
- Host-to-Network Layer- This is the lowest layer in TCP/IP model. The host has to connect to network using some protocol, so that it can send IP packets over it. This protocol varies from host to host and network to network.
Protocols used: ARPANET, SATNET, LAN, packet radio are the protocols which are used in this layer.
Domain Name System Architecture
The Domain name system comprises of Domain Names, Domain Name Space, Name Server that have been described below:
Domain Names- Domain Name is a symbolic string associated with an IP address. There are several domain names available; some of them are generic such as com, edu, gov, net etc, while some country level domain names such as au, in, za, us etc.
The Generic Top-Level Domain names- Com-Commercial business, Edu- Education, Gov– U.S. government agency, Int+ International entity, Mil– U.S. military, Net– Networking organization, Org- Non profit organization
The Country top-level domain names- Au– Australia, in – India, cl– Chile, fr– France, us– United States, za– South Africa, uk– United Kingdom, jp+ Japan, es- Spain, de– Germany, ca– Canada, ee– Estonia, hk– Hong Kong
Domain Name Space- The domain name space refers a hierarchy in the internet naming structure. This hierarchy has multiple levels (from 0 to 127), with a root at the top.
Name Server- Name server contains the DNS database. This database comprises of various names and their corresponding IP addresses. Since it is not possible for a single server to maintain entire DNS database, therefore, the information is distributed among many DNS servers. Hierarchy of server is same as hierarchy of names. The entire name space is divided into the zones
Zones- Zone is collection of nodes (sub domains) under the main domain. The server maintains a database called zone file for every zone. The information about the nodes in the sub domain is stored in the servers at the lower levels however; the original server keeps reference to these lower levels of servers.
Types of Name Servers
These are the three categories of Name Servers that manages the entire Domain Name System- Root Server, Primary Server and Secondary Server
- Root Server- Root Server is the top level server which consists of the entire DNS tree. It does not contain the information about domains but delegates the authority to the other server
- Primary Servers- Primary Server stores a file about its zone. It has authority to create, maintain, and update the zone file.
- Secondary Server- Secondary Server transfers complete information about a zone from another server which may be primary or secondary server. The secondary server does not have authority to create or update a zone file.
DNS Working
DNS translates the domain name into IP address automatically. Here the steps included in domain resolution process- 1. When we type www.ucidreamt.com into the browser, it asks the local DNS Server for its IP address. 2. Here the local DNS is at ISP end. 3. When the local DNS does not find the IP address of requested domain name, it forwards the request to the root DNS server and again enquires about IP address of it. 4. The root DNS server replies with delegation that I do not know the IP address of www.tutorialspoint.com but know the IP address of DNS Server. 5. The local DNS server then asks the com DNS Server the same question. 6. The com DNS Server replies the same that it does not know the IP address of www.tutorialspont.com but knows the address of tutorialspoint.com. 7. Then the local DNS asks the tutorialspoint.com DNS server the same question. 8. Then ucidream.com DNS server replies with IP address of www.ucidream.com. 9. Now, the local DNS sends the IP address of www.ucidream.com to the computer that sends the request.
Internet Services
- Communication Services- There are various Communication Services available that offer exchange of information with individuals or groups. These are various these services:
- Electronic Mail- Used to send electronic message over the internet.
- Telnet- Used to log on to a remote computer that is attached to internet.
- Newsgroup- Offers a forum for people to discuss topics of common interests.
- Internet Relay Chat (IRC)- Allows the people from all over the world to communicate in real time.
- Mailing Lists- Used to organize group of internet users to share common information through e-mail.
- Internet Telephony (VoIP)- Allows the internet users to talk across internet to any PC equipped to receive the call.
- Instant Messaging- Offers real time chat between individuals and group of people. Eg. Yahoo messenger, MSN messenger.
- Information Retrieval Services- There exist several Information retrieval services offering easy access to information present on the internet. These are various these services:
- File Transfer Protocol (FTP)- Enable the users to transfer files.
- Archie- It’s updated database of public FTP sites and their content. It helps to search a file by its name.
- Gopher- Used to search, retrieve, and display documents on remote sites.
- Very Easy Rodent Oriented Netwide Index to Computer Achieved (VERONICA)- VERONICA is gopher-based resource. It allows access to the information resource stored on gopher’s servers.
- Web Services- Web services allow exchange of information between applications on the web. Using web services, applications can easily interact with each other. The web services are offered using concept of Utility Computing.
- World Wide Web (WWW)- WWW is also known as W3. It offers a way to access documents spread over the several servers over the internet. These documents may contain texts, graphics, audio, video, hyperlinks. The hyperlinks allow the users to navigate between the documents.
- Video Conferencing- Video conferencing or Video teleconferencing is a method of communicating by two-way video and audio transmission with help of telecommunication technologies.
Modes of Video Conferencing
- Point-to-Point- This mode of conferencing connects two locations only.
- Multi-point- This mode of conferencing connects more than two locations through Multi-point Control Unit (MCU).
Internet Protocols
- Transmission Control Protocol (TCP)- Transmission Control Protocol (TCP) corresponds to the Transport Layer of OSI Model. TCP is a reliable and connection-oriented protocol.
TCP offers- Stream Data Transfer, Reliability, Efficient Flow Control, Full-duplex operation and Multiplexing. TCP offers connection oriented end-to-end packet delivery. TCP ensures reliability by sequencing bytes with a forwarding acknowledgement number that indicates to the destination the next byte the source expect to receive. It retransmits the bytes not acknowledged with in specified time period.
- Internet Protocol (IP)- Internet Protocol is connectionless and unreliable protocol. It ensures no guarantee of successfully transmission of data. In order to make it reliable, it must be paired with reliable protocol such as TCP at the transport layer.
- User Datagram Protocol (UDP)- Like IP, UDP is connectionless and unreliable protocol. It doesn’t require making a connection with the host to exchange data. Since UDP is unreliable protocol, there is no mechanism for ensuring that data sent is received. UDP transmits the data in form of a datagram. The UDP datagram consists of five parts as shown in the following diagram:
- File Transfer Protocol (FTP)- FTP is used to copy files from one host to another. FTP offers the mechanism for the same in following manner:
FTP creates two processes such as Control Process and Data Transfer Process at both ends i.e., at client as well as at server. FTP establishes two different connections: one is for data transfer and other is for control information. Control connection is made between control processes while Data Connection is made between<=”” b=””>. FTP uses port 21 for the control connection and Port 20 for the data connection.
- Trivial File Transfer Protocol (TFTP)- Trivial File Transfer Protocol is also used to transfer the files but it transfers the files without authentication. Unlike FTP, TFTP does not separate control and data information. Since there is no authentication exists, TFTP lacks in security features therefore it is not recommended to use TFTP.
Key points- TFTP makes use of UDP for data transport. Each TFTP message is carried in separate UDP datagram. The first two bytes of a TFTP message specify the type of message. The TFTP session is initiated when a TFTP client sends a request to upload or download a file. The request is sent from an ephemeral UDP port to the UDP port 69 of an TFTP server.
- Telnet- Telnet is a protocol used to log in to remote computer on the internet. There are a number of Telnet clients having user friendly user interface. The following diagram shows a person is logged in to computer A, and from there, he remote logged into computer B.
- Hyper Text Transfer Protocol (HTTP)- HTTP is a communication protocol. It defines mechanism for communication between browser and the web server. It is also called request and response protocol because the communication between browser and server takes place in request and response pairs.
- HTTP request comprises of lines which contains- Request line, Header Fields and Message body
Key Points- The first line i.e. the Request line specifies the request method i.e. Get or Post. The second line specifies the header which indicates the domain name of the server from where index.htm is retrieved.
- HTTP Response- Like HTTP request, HTTP response also has certain structure. HTTP response contains- Status line, Headers and Message body
Email is a service which allows us to send the message in electronic mode over the internet. It offers an efficient, inexpensive and real time mean of distributing information among people.
E-mail Protocols
- SMPTP- SMTP stands for Simple Mail Transfer Protocol. It was first proposed in 1982. It is a standard protocol used for sending e-mail efficiently and reliably over the internet.
Key Points- SMTP is application level protocol. SMTP is connection oriented protocol. SMTP is textbased protocol. It handles exchange of messages between e-mail servers over TCP/IP network. Apart from transferring e-mail, SMPT also provides notification regarding incoming mail. When you send e-mail, your e-mail client sends it to your e-mail server which further contacts the recipient mail server using SMTP client. These SMTP commands specify the sender’s and receiver’s e-mail address, along with the message to be send. The exchange of commands between servers is carried out without intervention of any user. In case, message cannot be delivered, an error report is sent to the sender which makes SMTP a reliable protocol.
- IMAP- IMAP stands for Internet Message Access Protocol. It was first proposed in 1986. There exist five versions of IMAP as follows- Original IMAP, IMAP2, IMAP3, IMAP2bis and IMAP4
Key Points- IMAP allows the client program to manipulate the e-mail message on the server without downloading them on the local computer. The e-mail is hold and maintained by the remote server. It enables us to take any action such as downloading, delete the mail without reading the mail. It enables us to create, manipulate and delete remote message folders called mail boxes. IMAP enables the users to search the e-mails. It allows concurrent access to multiple mailboxes on multiple mail servers.
- POP- POP stands for Post Office Protocol. It is generally used to support a single client. There are several versions of POP but the POP 3 is the current standard.
- Key Points- POP is an application layer internet standard protocol. Since POP supports offline access to the messages, thus requires less internet usage time. POP does not allow search facility. In order to access the messaged, it is necessary to download them. It allows only one mailbox to be created on server. It is not suitable for accessing non mail data. POP commands are generally abbreviated into codes of three or four letters. Eg. STAT.
- E-mail Security
E-mail Hacking- Email hacking can be done in any of the following ways- Spam, Virus and Phishing
- Spam- E-mail spamming is an act of sending Unsolicited Bulk E-mails (UBI) which one has not asked for. Email spams are the junk mails sent by commercial companies as an advertisement of their products and services.
- Virus- Some emails may incorporate with files containing malicious script which when run on your computer may lead to destroy your important data.
- Phishing- Email phishing is an activity of sending emails to a user claiming to be a legitimate enterprise. Its main purpose is to steal sensitive information such as usernames, passwords, and credit card details. Such emails contain link to websites that are infected with malware and direct the user to enter details at a fake website whose look and feels are same to legitimate one.
- E-mail Spamming and Junk Mails- Email spamming is an act of sending Unsolicited Bulk E-mails (UBI) which one has not asked for. Email spams are the junk mails sent by commercial companies as an advertisement of their products and services.
- Spams may cause the following problems- It floods your e-mail account with unwanted e-mails, which may result in loss of important e-mails if inbox is full. Time and energy is wasted in reviewing and deleting junk emails or spams. It consumes the bandwidth that slows the speed with which mails are delivered. Some unsolicited email may contain virus that can cause harm to your computer.
E-mail Providers– There are several email service providers available in the market with their enabled features such as sending, receiving, drafting, storing an email and much more.
The popular email service providers– Gmail, Hotmail, Yahoo Mail, iCloud Mail, ATM Mai, Mail.com and GMX Mail, Short-mail, Inbox.com, Facebook Messages, My Way Mail etc.
Website Designing
Web designing has direct link to visual aspect of a web site. Effective web design is necessary to communicate ideas effectively. Web designing is subset of web development. However, these terms are used interchangeably.
Wireframe- Wireframe refers to a visual guide to appearance of web pages. It helps to define structure of web site, linking between web pages and layout of visual elements.
Web development
Web development refers to building website and deploying on the web. Web development requires use of scripting languages both at the server end as well as at client end.
Web Development Process– Web development process includes all the steps that are good to take to build an attractive, effective and responsive website.
- Web development tools+ Web development tools helps the developer to test and debug the web sites. Now a days the web development tooll come with the web browsers as add-ons. All web browsers have built in tools for this purpose. These tools allow the web developer to use HTML, CSS and JavaScript etc.. These are accessed by hovering over an item on a web page and selecting the “Inspect Element” from the context menu.
- Features- Following are the common featuers that every web development tool exhibits:
- HTML and the DOM- HTML and DOM viewer allows you to see the DOM as it was rendered. It also allows to make changes to HTML and DOM and see the changes reflected in the page after the change is made.
Websites Hosting
Web hosting is a service of providing online space for storage of web pages. These web pages are made available via World Wide Web. The companies which offer website hosting are known as Web hosts. The servers on which web site is hosted remain switched on 24 x7. These servers are run by web hosting companies. Each server has its own IP address. Since IP addresses are difficult to remember therefore, webmaster points their domain name to the IP address of the server their website is stored on. It is not possible to host your website on your local computer, to do so you would have to leave your computer on 24 hours a day. This is not practical and cheaper as well. This is where web hosting companies comes in. Types of Hosting availed as per the need-
- Shared Hosting- In shared hosting, the hosting company puts thousand of website on the same physical server. Each customer has their own allocation of physical web space and a set of bandwidth limit. As all websites share same physical memory, MYSQL server and Apache server, one website on the server experiencing high traffic load will affect performance of all websites on the server.
- Virtual Private Server (VPS)- It is also known as Virtual Dedicated Server. It is a server which is partitioned into smaller servers. In this customer is given their own partition, which is installed with its own operating system. Unlike shared hosting, VPS doesn’t share memory or processor time rather it allocates certain amount of memory and CPU to use which means that any problem on a VPS partition on the same drive will not affect other VPS customers.
- Dedicated Server- In this kind of hosting, single dedicated server is setup for just one customer. It is commonly used by the businesses that need the power, control and security that a dedicated server offers.
- Reseller Hosting- A reseller acts as a middle man and sells hosting space of someone else’s server.
- Grid Hosting- Instead of utilizing one server, Grid Hosting spreads resources over a large number of servers. It is quite stable and flexible. The servers can be added or taken away from the grid without crashing the system.
World Wide Web
A technical definition of the World Wide Web is: all the resources and users on the Internet that are using the Hypertext Transfer Protocol (HTTP). A broader definition comes from the organization that Web inventor Tim Berners-Lee helped found, the World Wide Web Consortium (W3C). The World Wide Web is the universe of network-accessible information, an embodiment of human knowledge. In simple terms, The World Wide Web is a way of exchanging information between computers on the Internet, tying them together into a vast collection of interactive multimedia resources. Internet and Web is not the same thing: Web uses internet to pass over the information.
WWW Evolution- World Wide Web was created by Timothy Berners Lee in 1989 at CERN in Geneva. World Wide Web came into existence as a proposal by him, to allow researchers to work together effectively and efficiently at CERN. Eventually it became World Wide Web.
Identifiers and Character Set- Uniform Resource Identifier (URI) is used to uniquely identify resources on the web and UNICODE makes it possible to built web pages that can be read and write in human languages.
Syntax- XML (Extensible Markup Language) helps to define common syntax in semantic web.
Data Interchange+ Resource Description Framework (RDF) framework helps in defining core representation of data for web. RDF represents data about resource in graph form.
Taxonomies- RDF Schema (RDFS) allows more standardized description of taxonomies and other ontological constructs.
Ontologies– Web Ontology Language (OWL) offers more constructs over RDFS. It comes in following three versions- OWL Lite for taxonomies and simple constraints. OWL DL for full description logic support. OWL for more syntactic freedom of RDF
Rules– RIF and SWRL offers rules beyond the constructs that are available from RDFs and OWL. Simple Protocol and RDF Query Language (SPARQL) is SQL like language used for querying RDF data and OWL Ontologies.
Proof- All semantic and rules that are executed at layers below Proof and their result will be used to prove deductions.
Cryptography- Cryptography means such as digital signature for verification of the origin of sources is used.
WWW Operation- WWW works on client- server approach. Here explains how the web works: User enters the URL (say, https://www.ucidream.com) of the web page in the address bar of web browser. Then browser requests the Domain Name Server for the IP address corresponding to www.ucidream.com. After receiving IP address, browser sends the request for web page to the web server using HTTP protocol which specifies the way the browser and web server communicates. Then web server receives request using HTTP protocol and checks its search for the requested web page. If found it returns it back to the web browser and close the HTTP connection. Now the web browser receives the web page, It interprets it and display the contents of web page in web browser’s window.
Web Browsers
web Browser is an application software that allows us to view and explore information on the web. User can request for any web page by just entering a URL into address bar. Web browser can show text, audio, video, animation and more. It is the responsibility of a web browser to interpret text and commands contained in the web page. Earlier the web browsers were text-based while now a days graphical-based or voice-based web browsers are also available. Web browser available today- Internet Explorer, Google Chrome, Mozilla Firefox, Netscape Navigator, Opera, Safari, Sea Monkey, K-meleon.
Web Server
Web server is a computer where the web content is stored. y web server is used to host the web sites but there exist other web servers also such as gaming, storage, FTP, email etc. Web site is collection of web pages while web server is a software that respond to the request for web resources.
Web Server Working- Web server respond to the client request in either of the following two ways- Sending the file to the client associated with the requested URL. Generating response by invoking a script and communicating with database
Key Points- When client sends request for a web page, the web server search for the requested page if requested page is found then it will send it to client with an HTTP response. If the requested web page is not found, web server will the send an HTTP response: Error 404 Not found. If client has requested for some other resources, then the web server will contact to the application server and data store to construct the HTTP response.
Architecture- Web Server Architecture follows the following two approaches:
- Concurrent Approach- Concurrent approach allows the web server to handle multiple client requests at the same time. It can be achieved by following methods:
- Multi-processing– In this a single process (parent process) initiates several single-threaded child processes and distribute incoming requests to these child processes. Each of the child processes are responsible for handling single request. It is the responsibility of parent process to monitor the load and decide if processes should be killed or forked.
- Multi-threaded- Unlike Multi-process, it creates multiple single-threaded process.
- Hybrid– It is combination of above two approaches. In this approach multiple process are created and each process initiates multiple threads. Each of the threads handles one connection. Using multiple threads in single process results in less load on system resources.
Proxy Server
Proxy server is an intermediary server between client and the internet. Proxy servers offers the following basic functionalities- Firewall and network data filtering. Network connection sharing. Data caching. Proxy servers allow to hide, conceal and make your network id anonymous by hiding your IP address.
Purpose of Proxy Servers- Following are the reasons to use proxy servers- Monitoring and Filtering, improving performance, Translation, Accessing services anonymously and Security.
Type of Proxies:
- Forward Proxies- In this the client requests its internal network server to forward to the internet. Open Proxies- Open Proxies helps the clients to conceal their IP address while browsing the web.
- Reverse Proxies- In this the requests are forwarded to one or more proxy servers and the response from the proxy server is retrieved as if it came directly from the original Server.
- Proxy server listener- It is the port where new request from the client browser is listened. This module also performs blocking of clients from the list given by the user.
- Connection Manager- It contains the main functionality of the proxy server. It performs the following functions:
- It contains the main functionality of the proxy server. It performs the following functions- Read request from header of the client., Parse the URL and determine whether the URL is blocked or not, Generate connection to the web server, Read the reply from the web server, If no copy of page is found in the cache then download the page from web server else will check its last modified date from the reply header and accordingly will read from the cache or server from the web, Then it will also check whether caching is allowed or not and accordingly will cache the page.
- Cache Manager- This module is responsible for storing, deleting, clearing and searching of web pages in the cache.
- Log Manager- This module is responsible for viewing, clearing and updating the logs.
- Configuration- This module helps to create configuration settings which in turn let other modules to perform desired configurations such as caching.
Search Engines
Search Engine refers to a huge database of internet resources such as web pages, newsgroups, programs, images etc. It helps to locate information on World Wide Web. User can search for any information by passing query in form of keywords or phrase. It then searches for relevant information in its database and return to the user.
Search Engine Components-There are three basic components of a search engine Web Crawler, Database and Search Interfaces
- Web crawler- It is also known as spider or bots. It is a software component that traverses the web to gather information.
- Database- All the information on the web is stored in database. It consists of huge web resources.
- Search Interfaces- This component is an interface between user and the database. It helps the user to search through the database.
Internet Collaboration
- Online Chatting- Online chatting is a text-based communication between two or more people over the network. In this, the text message is delivered in real time and people get immediate response. Telomeric was the world first online chat system. It was developed by Doug Brown and David R. Woolley in 1973.
- Instant Messaging (IM)- Instant messaging is a software utility that allows IM users to communicate by sending text messages, files, and images.
- Internet Relay Chat (IRC)- Internet Relay Chat is a protocol developed by Oikarinen in August 1988. It defines set of rules for communication between client and server by some communication mechanism such as chat rooms, over the internet. IRC consist of separate networks of IRC servers and machines. These allow IRC clients to connect to IRC. IRC client runs a program client to connect to a server on one of the IRC nets. After connecting to IRC server on IRC network, user can join with one or more channels and converse over there.
- Video Conferencing- Video conferencing or Video teleconferencing is a method of communicating by two-way video and audio transmission with help of telecommunication technologies.
Modes of Video Conferencing
- Point-to-Point- This mode of conferencing connects two locations only.
- Multi-point- This mode of conferencing connects more than two locations through Multi-point Control Unit (MCU).
- Video Sharing- Video sharing is an IP Multimedia System (IMS) service that allows user to switch voice calls to unidirectional video streaming session. The video streaming session can be initiated by any of the parties. Moreover, the video source can be the camera or the pre-recorded video clip.
Mailing List
In order to send same email to a group of people, an electron list is created which is know as Mailing List. It is the list server which receives and distributes postings and automatically manages subscriptions. Mailing list offers a forum, where users from all over the globe can answer questions and have them answered by others with shared interests.
Types of Mailing List- The various types of mailing lists:
- Response List- It contains the group of people who have responded to an offer in some way. These people are the customers who have shown interest in specific product or service.
- Compiled List- The compiled list is prepared by collecting information from various sources such as surveys, telemarketing etc.
- Announcements- These lists are created for sending out coupans, new product announcements and other offers to the customers.
- Discussion List- This list is created for sharing views on a specific topic suchas computer, environment, health, education etc.
Usenet (USEr NETwork)
Like mailing lists Usenet is also a way of sharing information. It was started by Tom Truscott and Jim Ellis in 1979. Initially it was limited to two sites but today there are thousands of Usenet sites involving millions of people. Usenet is a kind of discussion group where people can share views on topic of their interest. The article posted to a newsgroup becomes available to all readers of the newsgroup.
Students Note
UCI – Education
Welcome To You
Fundamental
- The word computer comes from the word “compute”, which means, “to calculate”. Thereby, a computer is an electronic device that can perform arithmetic operations at high speed. A computer is also called a data processor because it can store, process, and retrieve data whenever desired. The activity of processing data using a computer is called data processing
- Computer can perform data processing jobs very fast, usually measured in microseconds (10-6), nanoseconds (10-9), and picoseconds (10-12)
- Blaise Pascal invented the first mechanical adding machine in 1642
- Baron Gottfried Wilhelm von Leibniz invented the first calculator for multiplication in 1671
- Keyboard machines originated in the United States around 1880
- Around 1880, Herman Hollerith came up with the concept of punched cards that were extensively used as input media until late 1970s
- Charles Babbage is considered to be the father of modern digital computers
- He designed “Difference Engine” in 1822
- He designed a fully automatic analytical engine in 1842 for performing basic arithmetic function. His efforts established a number of principles that are fundamental to the design of any digital computer
- The Mark I Computer (1937-44)- The IBM Automatic Sequence Controlled Calculator (ASCC), called Mark I by Harvard University’s staff, was a general-purpose electromechanical computer. One of the first programs to run on the Mark I was initiated on 29 March 1944 by John von Neumann.
- The Atanasoff-Berry Computer (1939-42)- The Atanasoff–Berry computer (ABC) was the first automatic electronic digital computer.
- The ENIAC (1943-46)- Electronic Numerical Integrator and Computer was the first programmable, electronic, general-purpose digital computer. It was Turing-complete, and able to solve “a large class of numerical problems” through reprogramming.
- The EDVAC (1946-52)- EDVAC (Electronic Discrete Variable Automatic Computer) was one of the earliest electronic computers. Unlike its predecessor the ENIAC, it was binary rather than decimal, and was designed to be a stored-program computer. ENIAC inventors John Mauchly and J. Presper Eckert proposed.
- The EDSAC (1947-49)- The Electronic delay storage automatic calculator (EDSAC) was an early British computer. Inspired by John von Neumann’s seminal First Draft of a Report on the EDVAC, the machine was constructed by Maurice Wilkes the University of Cambridge Mathematical Laboratory.
- Manchester Mark I (1948)- The Manchester Mark 1 was one of the earliest stored-program computers, developed at the Victoria University of Manchester from the Manchester Baby.
- The UNIVAC I (1951)- The UNIVAC I (UNIVersal Automatic Computer I) was the first general-purpose electronic digital computer design for business application. It was designed principally by J. Presper Eckert and John Mauchly, the inventors of the ENIAC.
- Inputting. The process of entering data and instructions into the computer system
- Storing. Saving data and instructions to make them readily available for initial or additional processing whenever required
- Processing. Performing arithmetic operations (add, subtract, multiply, divide, etc.) or logical operations (comparisons like equal to, less than, greater than, etc.) on data to convert them into useful information
- Outputting. The process of producing useful information or results for the user such as a printed report or visual display
- Controlling. Directing the manner and sequence in which all of the above operations are performed
- Non–positional number systems- Use symbols such as I for 1, II for 2, III for 3, IIII for 4, IIIII for 5, etc. Each symbol represents the same value regardless of its position in the number. The symbols are simply added to find out the value of a particular number.
- Positional number systems- Use only a few symbols called digits. These symbols represent different values depending on the position they occupy in the number.
- Decimal Number System- A positional number system. Has 10 symbols or digits (0, 1, 2, 3, 4, 5, 6, 7,8,9). Hence, its base = 10. The maximum value of a single digit is 9 (one less than the value of the base), Each position of a digit represents a specific power of the base (10). We use this number system in our day-to-day life
- Binary Number System- A positional number system. Has only 2 symbols or digits (0 and 1). Hence its base = 2. The maximum value of a single digit is 1 (one less than the value of the base). Each position of a digit represents a specific power of the base (2). This number system is used in computers
- Bit- Bit stands for binary digit. A bit in computer terminology means either a 0 or a 1. A binary number consisting of n bits is called an n-bit number.
- Octal Number System-A positional number system. Has total 8 symbols or digits (0, 1, 2, 3, 4, 5, 6, 7). Hence, its base = 8. The maximum value of a single digit is 7 (one less than the value of the base. Each position of a digit represents a specific power of the base (8). Since there are only 8 digits, 3 bits (23 = 8) are sufficient to represent any octal number in binary.
- Hexa-decimal Number System- A positional number system. Has total 16 symbols or digits (0, 1, 2, 3, 4, 5, 6, 7, 8, 9, A, B, C, D, E, F). Hence its base = 16. The symbols A, B, C, D, E and F represent the decimal values 10, 11, 12, 13, 14 and 15 respectively. The maximum value of a single digit is 15 (one less than the value of the base). Each position of a digit represents a specific power of the base (16). Since there are only 16 digits, 4 bits (24 = 16) are sufficient to represent any hexadecimal number in binary.
- Computer Codes- Computer codes are used for internal representation of data in computers. As computers use binary numbers for internal data representation, computer codes use binary coding schemes. In binary coding, every symbol that appears in the data is represented by a group of bits. The group of bits used to represent a symbol is called a Byte. As most modern coding schemes use 8 bits to represent a symbol, the term byte is often used to mean a group of 8 bits.
- BCD- BCD stands for Binary Coded Decimal. It is one of the early computer codes. It uses 6 bits to represent a symbol. It can represent 64 (26) different characters
- EBCDIC- EBCDIC stands for Extended Binary Coded Decimal Interchange Code. It uses 8 bits to represent a symbol. It can represent 256 (28) different characters. Zoned decimal numbers are used to represent numeric values (positive, negative, or unsigned) in EBCDIC. A sign indicator (C for plus, D for minus, and F for unsigned) is used in the zone position of the rightmost digit. Zones for all other digits remain as F, the zone value for numeric characters in EBCDIC. In zoned format, there is only one digit per byte.
- ASCII- ASCII stands for American Standard Code for Information Interchange. ASCII is of two types – ASCII-7 and ASCII-8.
- ASCII-7 uses 7 bits to represent a symbol and can represent 128 (27) different characters.
- ASCII-8- uses 8 bits to represent a symbol and can represent 256 (28) different characters. First 128 characters in ASCII-7 and ASCII-8 are same
- Unicode- Provides a consistent way of encoding multilingual plain text. Defines codes for characters used in all major languages of the world. Defines codes for special characters, mathematical symbols, technical symbols, and diacritics. Capacity to encode as many as a million characters. Assigns each character a unique numeric value and name. Encoding Forms- o UTF-8, UTF-16, UTF-32.
- Central Processing Unit (CPU)- The brain of a computer system. Performs all major calculations and comparisons. Activates and controls the operations of other units of a computer system.
- Two basic components are Control Unit (CU) and Arithmetic Logic Unit (ALU)
- Control Unit (CU)- One of the two basic components of CPU. Acts as the central nervous system of a computer system. Selects and interprets program instructions, and coordinates execution. Has some special purpose registers and a decoder to perform these activities.
- Arithmetic Logic Unit (ALU)- One of the two basic components of CPU. Actual execution of instructions takes place in ALU. Has some special purpose registers. Has necessary circuitry to carry out all the arithmetic and logic operations included in the CPU instruction set.
- Instruction Set- CPU has built-in ability to execute a particular set of machine instructions, called its instruction set. Most CPUs have 200 or more instructions (such as add, subtract, compare, etc.) in their instruction set. CPUs made by different manufacturers have different instruction sets. Manufacturers tend to group their CPUs into “families” having similar instruction sets. New CPU whose instruction set includes instruction set of its predecessor CPU is said to be backward compatible with its predecessor
- Registers- Special memory units, called registers, are used to hold information on a temporary basis as the instructions are interpreted and executed by the CPU. Registers are part of the CPU (not main memory) of a computer. The length of a register, sometimes called its word size, equals the number of bits it can store. With all other parameters being the same, a CPU with 32-bit registers can process data twice larger than one with 16-bit registers.
- Memory Address (MAR)- Holds address of the active memory location
- Memory Buffer (MBR)- Holds contents of the accessed (read/written) memory word
- Program Control (PC)- Holds address of the next instruction to be executed
- Accumulator (A)- Holds data to be operated upon, intermediate results, and the results
- Instruction (I)- Holds an instruction while it is being executed
- Input/output (I/O)- Used to communicate with the I/O devices
- Processor Speed- Computer has a built-in system clock that emits millions of regularly spaced electric pulses per second (known as clock cycles). It takes one cycle to perform a basic operation, such as moving a byte of data from one memory location to another. Clock speed (number of clock cycles per second) is measured in Megahertz (106 cycles/sec) or Gigahertz (109 cycles/sec)
- CISC (Complex Instruction Set Computer)- Mostly used in personal computers. Large instruction set. Variable-length instructions. Variety of addressing modes. Complex & expensive to produce
- RISC (Reduced Instruction Set Computer)- Mostly used in workstations. Small instruction set. Fixed-length instructions. Reduced references to memory to retrieve operands
- EPIC (Explicitly Parallel Instruction Computing)- Mostly used in high-end servers and workstation. Allows software to communicate explicitly to the processor when operations are parallel. Uses tighter coupling between the compiler and the processor. Enables compiler to extract maximum parallelism in the original code, and explicitly describe it to the processor
- Multi-Core Processor- Mostly used in high-end servers and workstations. Processor chip has multiple cooler-running, more energy- efficient processing cores. Improve overall performance by handling more work in parallel. can share architectural components, such as memory elements and memory management.
- Main Memory- Every computer has a temporary storage built into the computer hardware. It stores instructions and data of a program mainly when the program is being executed by the CPU. This temporary storage is known as main memory, primary storage, or simply memory. Physically, it consists of some chips either on the motherboard or on a small circuit board attached to the motherboard of a computer. It has random access property. It is volatile.
- Memory Capacity- Memory capacity of a computer is equal to the number of bytes that can be stored in its primary storage. Its units are:
- Kilobytes (KB) : 1024 (210) bytes
- Megabytes (MB) : 1,048,576 (220) bytes
- Gigabytes (GB) : 1,073,741824 (230) bytes
- Random Access Memory (RAM)- Primary storage of a computer is often referred to as RAM because of its random-access capability. RAM chips are volatile memory. A computer’s motherboard is designed in a manner that the memory capacity can be enhanced by adding more memory chips. The additional RAM chips, which plug into special sockets on the motherboard, are known as single-in-line memory modules (SIMMs)
- Read Only Memory (ROM)- ROM a non-volatile memory chip. Data stored in a ROM can only be read and used – they cannot be changed. ROMs are mainly used to store programs and data, which do not change and are frequently used. For example, system boot program.
- Manufacturer-programmed ROM- Data is burnt by the manufacturer of the electronic equipment in which it is used.
- User-programmed ROM or Programmable ROM (PROM)- The user can load and store “read-only” programs and data in it
- Erasable PROM (EPROM)- The user can erase information stored in it and the chip can be reprogrammed to store new information
- Ultra Violet EPROM (UVEPROM)- A type of EPROM chip in which the stored information is erased by exposing the chip for some time to ultra-violet light
- Electrically EPROM (EEPROM) or Flash memory- A type of EPROM chip in which the stored information is erased by using high voltage electric pulses
- Cache Memory- It is commonly used for minimizing the memory- processor speed mismatch. It is an extremely fast, small memory between CPU and main memory whose access time is closer to the processing speed of the CPU. It is used to temporarily store very active data and instructions during processing. Cache is pronounced as “cash”
- Direct-access Storage Devices- Approximately equal access time is required for accessing information from any storage location. Suitable for direct processing applications such as on- line ticket booking systems, on-line banking systems.
- Sequential-access Storage Devices- Arrival at the desired storage location may be preceded by sequencing through other locations. Data can only be retrieved in the same sequence in which it is stored. Access time varies according to the storage location of the information being accessed
- Magnetic Tape Basics- Commonly used sequential-access secondary storage device. Physically, the tape medium is a plastic ribbon, which is usually ½ inch or ¼ inch wide and 50 to 2400 feet long. Plastic ribbon is coated with a magnetizable recording material such as iron-oxide or chromium dioxide. Data are recorded on the tape in the form of tiny invisible magnetized and non-magnetized spots (representing 1s and 0s) on its coated surface. Tape ribbon is stored in reels or a small cartridge or cassette
- Magnetic Disk – Basics- Commonly used direct-access secondary storage device. Physically, a magnetic disk is a thin, circular plate/platter made of metal or plastic that is usually coated on both sides with a magnetizable recording material such as iron-oxide. Data are recorded on the disk in the form of tiny invisible magnetized and non-magnetized spots (representing 1s and 0s) on the coated surfaces of the disk. The disk is stored in a specially designed protective envelope or cartridge, or several of them are stacked together in a sealed, contamination-free container.
- Optical Disk – Basics- Consists of a circular disk, which is coated with a thin metal or some other material that is highly reflective. Laser beam technology is used for recording/reading of data on the disk. Also known as laser disk / optical laser disk, due to the use of laser beam technology. Proved to be a promising random-access medium for high-capacity secondary storage because it can store extremely large amounts of data in a limited space.
- Optical Character Recognition (OCR) Device- Scanner equipped with a character recognition software (called OCR software) that converts the bit map images of characters to equivalent ASCII codes. Enables word processing of input text and also requires less storage for storing the document as text rather than an image
- Optical Mark Reader (OMR)- Scanner capable of recognizing a pre-specified type of mark by pencil or pen. Very useful for grading tests with objective type questions, or for any input data that is of a choice or selection nature.
- Bar-code Reader– Scanner used for reading (decoding) bar-coded data. Bar codes represent alphanumeric data by a combination of adjacent vertical lines (bars) by varying their width and the spacing between them.
- Magnetic-Ink Character Recognition (MICR)- MICR is used by banking industry for faster processing of large volume of cheques. Bank’s identification code (name, branch, etc.), account number and cheque number are pre-printed (encoded) using characters from a special character set on all chequeens.
- Digitizer- Input device used for converting (digitizing) pictures, maps and drawings into digital form for storage in computers. Commonly used in the area of Computer Aided Design (CAD) by architects and engineers to design cars, buildings medical devices, robots, mechanical parts, etc.
- Electronic-cards based devices- Electronic cards are small plastic cards having encoded data appropriate for the application for which they are used. Electronic-card reader (normally connected to a computer) is used to read data encoded on an electronic card and transfer it to the computer for further processing.
- Speech recognition devices- Input device that allows a person to input data to a computer system by speaking to it.
- Monitors- Monitors are the most popular output devices used for producing soft-copy output. Cathode-ray-tube (CRT) monitors look like a television and are normally used with non-portable computer systems. Flat-panel monitors are thinner and lighter and are commonly used with portable computer systems like notebook computers. Now they are also used with non- portable desktop computer systems because they occupy less table space.
- Plotters- Plotters are an ideal output device for architects, engineers, city planners, and others who need to routinely generate high-precision, hard-copy graphic output of widely varying sizes.
- Laser Printers- Page printers that print one page at a time. Consist of a laser beam source, a multi-sided mirror, a photoconductive drum and toner (tiny particles of oppositely charged ink). To print a page, the laser beam is focused on the electro statically charged drum by the spinning multi-sided mirror
- Notebook Computers- Portable computers mainly meant for use by people who need computing resource wherever they go.
- Personal Computers (PCs)- Non-portable, general-purpose computer that fits on a normal size office table.
- Workstations- Powerful desktop computer designed to meet the computing needs of engineers, architects, and other professionals. Provides greater processing power, larger storage, and better graphics display facility than PCs. Commonly used for computer-aided design, multimedia applications, simulation of complex scientific and engineering problems, and visualization.
- Mainframe Systems- Mainly used by large organizations as banks, insurance companies, hospitals, railways, etc. Used for data handling and information processing requirements. Used in such environments where a large number of users need to share a common computing facility. Typically consist of a host computer, front-end computer, back-end computer, console terminals, magnetic disk drives, tape drives, magnetic tape library, user terminals, printers, and plotters.
- Supercomputers- Most powerful and most expensive computers available at a given time. Primarily used for processing complex scientific applications that require enormous processing power. Analysis of large volumes of seismic data. Supercomputers also support multiprogramming.
- Parallel Processing Systems- Use multiprocessing and parallel processing technologies to solve complex problems faster. Also known as parallel computers or parallel processing systems. Modern supercomputers employ hundreds of processors and are also known as massively parallel processors.
- Client and Server Computers- Client-server computing environment has multiple clients, one/more servers, and a network. Client is a PC/workstation with user-friendly interface running client processes that send service requests to the server. Server is generally a relatively large computer that manages a shared resource and provides a set of shared user services to the clients.
- Handheld Computers- Small computing device that can be used by holding in hand, also known as palmtop.
- Software refers to a collection of programs. Program is a sequence of instructions written in a language that can be understood by a computer. Software package is a group of programs that solve a specific problem or perform a specific type of job.
- System Software- Make the operation of a computer system more effective and efficient. Help hardware components work together and provide support for the development and execution of application software. Programs included in a system software package are called system programs and programmers who prepare them are called system programmers
- Application Software- Solve a specific problem or do a specific task. Programs included in an application software package are called application programs and the programmers who prepare them are called application programmers
- Firmware- Firmware is software substituted for hardware and stored in read-only memory
- Firmware technology has enabled production of various types of smart machines having microprocessor chips with embedded software.
- Middleware- Act as “glue” between client and server parts of application. Provide programming abstraction. Mask heterogeneity of underlying network, hardware, and OS. Encourages three-tier software architecture against two- tier popularized by Server-Client architecture
- Machine language- Only language of a computer understood by it without using a translation program. Normally written as strings of binary 1s and 0s. Written using decimal digits if the circuitry of the computer being used permits this
- Assembly language- Using alphanumeric mnemonic codes instead of numeric codes for the instructions in the instruction set. Allowing storage locations to be represented in form of alphanumeric addresses instead of numeric addresses. Providing pseudo-instructions that are used for instructing the system how we want the program to be assembled inside the computer’s memory
- Assembler- Software that translates as assembly language program into an equivalent machine language program of a computer
- High-level language- Machine independent. Do not require programmers to know anything about the internal structure of computer on which high-level language programs will be executed. Deal with high-level coding, enabling the programmers to write instructions using English words and familiar mathematical symbols and expressions
- Compiler- Translator program (software) that translates a high- level language program into its equivalent machine language program. Compiles a set of machine language instructions for every program instruction in a high-level language
- Interpreter- Interpreter is a high-level language translator
- Takes one statement of a high-level language program, translates it into machine language instructions. Immediately executes the resulting machine language instructions Compiler simply translates the entire source program into an object program and is not involved in its execution
- Object-Oriented Programming Languages- Programming languages are used for simulating real- world problems on computers. Essence of OOP is to solve a problem by: Identifying the real-world objects of the problem, Identifying processing required of them.
- FORTRAN- Stands for FORmula TRANslation. Originally developed by John Backus and his team at IBM followed by several revisions. Designed for solving scientific & engineering problems.
- COBOL- Stands for COmmon Business Oriented Language. Originally developed started under Grace Hopper followed by COnference on DAta SYstems Languages (CODASYL). Designed for programming business data processing applications
- BASIC- Stands for Beginners All-purpose Symbolic Instruction Code. Developed by Professor John Kemeny and Thomas Kurtz at Darmouth College in the United States. Flexible and reasonably powerful language and can be used for both business and scientific applications
- Pascal- Developed by Professor Nicklaus Wirth of Federal Institute of Technology in Zurich. Suitable for both scientific & business applications
- C Language- Developed in 1972 at AT&T’s Bell laboratories, USA by Dennis Ritchie and Brian Kernighan. High-level programming languages (mainly machine independence) with the efficiency of an assembly language. Language of choice of programmers for portable systems software and commercial software packages like OS, compiler, spreadsheet, word processor, and database management systems
- C++ Language- C++ – C++ as ++ is increment operator and C language is incremented to its next level with C++. Developed by Bjarne Stroustrup at Bell Labs in the early 1980s
- Contains all elements of the basic C language. Expanded to include numerous object-oriented programming features
- Java- Development started at Sun Microsystems in 1991 by a team led by James Gosling. Developed to be similar to C++ with fewer features to keep it simple and easy to use. Compiled code is machine-independent and developed programs are simple to implement and use
- Bugs- Program errors are known as bugs
- Debugging- Process of detecting and correcting these errors is called debugging
- Testing – Testing is the process of making sure that the program performs the intended task
Operating System
Operating System
- An Operating System (OS) is an interface between a computer user and computer hardware.
- An operating system is a software which performs all the basic tasks like file management, memory management, process management, handling input and output, and controlling peripheral devices such as disk drives and printers.
- Some popular Operating Systems include Linux Operating System, Windows Operating System, VMS, OS/400, AIX, z/OS, etc.
- An Operating System provides services to both the users and to the programs.
- An Operating System provides programs an environment to execute.
- An Operating System provides users the services to execute the programs in a convenient manner.
- Services provided by an operating system are Program execution, I/O operations, File System manipulation, Communication, Error Detection, Resource Allocation and Protection.
- Operating systems handle many kinds of activities from user programs to system programs. Each of these activities is encapsulated as a process.
- A process includes the complete execution context (code to execute, data to manipulate, registers, OS resources in use).
- Definition- An operating system is a program that acts as an interface between the user and the computer hardware and controls the execution of all kinds of programs.
- Memory Management, Processor Management, Device Management, File Management, Security, Control over system performance, Job accounting, Error detecting aids, Coordination between other software and users.
- Memory management refers to management of Primary Memory or Main Memory.
- Main memory is a large array of words or bytes where each word or byte has its own address.
- Main memory provides a fast storage that can be accessed directly by the CPU.
- For a program to be executed, it must in the main memory.
- In multiprogramming environment, the OS decides which process gets the processor when and for how much time. This function is called process scheduling.
- An Operating System does the activities for Processor Management keeps tracks of processor and status of process. The program responsible for this task is known as traffic controller.
- An Operating System manages device communication via their respective drivers.
- An Operating System does the activities for device management keeps tracks of all devices. Program responsible for this task is known as the I/O controller.
- A file system is normally organized into directories for easy navigation and usage.
- An Operating System does the activities for file management keeps track of information, location, uses, status etc. The collective facilities are often known as file system.
- Operating systems are there from the very first computer generation and they keep evolving with time.
- The users of a batch operating system do not interact with the computer directly.
- In Batch operating system, each user prepares his job on an off-line device like punch cards and submits it to the computer operator.
- In Batch operating system, to speed up processing, jobs with similar needs are batched together and run as a group.
- Time-sharing Operating System is a technique which enables many people, located at various terminals, to use a particular computer system at the same time.
- Time-sharing Operating System or multitasking is a logical extension of multiprogramming.
- Processor’s time which is shared among multiple users simultaneously is termed as time-sharing.
- The main difference between Multiprogrammed Batch Systems and Time-Sharing Systems is that in case of Multiprogrammed batch systems, the objective is to maximize processor use, whereas in Time-Sharing Systems, the objective is to minimize response time.
- Time-sharing Operating System uses CPU scheduling and multiprogramming to provide each user with a small portion of a time.
- Distributed operating System use multiple central processors to serve multiple real-time applications and multiple users.
- Data processing jobs are distributed among the processors accordingly.
- In the Distributed operating System processors communicate with one another through various communication lines (such as high-speed buses or telephone lines).
- The Distributed operating System are referred as loosely coupled systems or distributed systems.
- In the Distributed operating System, processors are referred as sites, nodes, computers, and so on.
- The Distributed operating System with resource sharing facility, a user at one site may be able to use the resources available at another.
- The Distributed operating System speedup the exchange of data with one another via electronic mail.
- A Network Operating System runs on a server and provides the server the capability to manage data, users, groups, security, applications, and other networking functions.
- The Network Operating System, primary purpose of the network operating system is to allow shared file and printer access among multiple computers in a network, typically a local area network (LAN), a private network or to other networks.
- Examples of network operating systems include Microsoft Windows Server, UNIX, Linux, Mac OS X, Novell NetWare, and BSD.
- A real-time system is defined as a data processing system in which the time interval required to process and respond to inputs is so small that it controls the environment.
- Real-time system, the time taken by the system to respond to an input and display of required updated information is termed as the response time.
- A real-time operating system must have well-defined, fixed time constraints, otherwise the system will fail.
- There are two types of real-time operating systems.
- Hard real-time systems- Hard real-time systems guarantee that critical tasks complete on time. In hard real-time systems, secondary storage is limited or missing and the data is stored in ROM. In these systems, virtual memory is almost never found.
- Soft real-time systems- Soft real-time systems are less restrictive. A critical real-time task gets priority over other tasks and retains the priority until it completes. Soft real-time systems have limited utility than hard real-time systems. A file represents a collection of related information. The storage media include magnetic tape, magnetic disk and optical disk drives like CD, DVD. Batch processing is a technique in which an Operating System collects the programs and data together in a batch before processing starts.
- Multitasking
Multitasking is when multiple jobs are executed by the CPU simultaneously by switching between them. In Multitasking the user gives instructions to the operating system or to a program directly, and receives an immediate response. The OS handles multitasking in the way that it can handle multiple operations/executes multiple programs at a time. Multitasking Operating Systems are also known as Time-sharing systems. Multitasking Operating Systems were developed to provide interactive use of a computer system at a reasonable cost. A time-shared operating system uses the concept of CPU scheduling and multiprogramming to provide each user with a small portion of a time-shared CPU.
- Multiprogramming
Sharing the processor, when two or more programs reside in memory at the same time, is referred as multiprogramming. Multiprogramming assumes a single shared processor. Multiprogramming increases CPU utilization by organizing jobs so that the CPU always has one to execute. The operating system keeps several jobs in memory at a time. Multiprogramming operating systems monitor the state of all active programs and system resources using memory management programs to ensures that the CPU is never idle, unless there are no jobs to process.
- Interactivity
Interactivity refers to the ability of users to interact with a computer system. Interactivity provides the user an interface to interact with the system. The Interactivity, manages input devices to take inputs from the user. The Interactivity, manages output devices to show outputs to the user.
- Real Time System
Real-time systems are usually dedicated, embedded systems. The Real Time System, Operating Systems typically read from and react to sensor data.
- Distributed Environment
A distributed environment refers to multiple independent CPUs or processors in a computer system. A distributed environment the OS distributes computation logics among several physical processors. A distributed environment the processors do not share memory or a clock. Instead, each processor has its own local memory. A distributed environment the OS manages the communications between the processors. They communicate with each other through various communication lines.
- Spooling
Spooling is an acronym for simultaneous peripheral operations on line. Spooling refers to putting data of various I/O jobs in a buffer. This buffer is a special area in memory or hard disk which is accessible to I/O devices. handles I/O device data spooling as devices have different data access rates. Maintains the spooling buffer which provides a waiting station where data can rest while the slower device catches up. Maintains parallel computation because of spooling process as a computer can perform I/O in parallel fashion. The spooling operation uses a disk as a very large buffer. Spooling is capable of overlapping I/O operation for one job with processor operations for another job.
- Process- A process is basically a program in execution.
- Program- A program is a piece of code which may be a single line or millions of lines. A computer program is usually written by a computer programmer in a programming language. A computer program is a collection of instructions that performs a specific task when executed by a computer. When we compare a program with a process, we can conclude that a process is a dynamic instance of a computer program. A part of a computer program that performs a well-defined task is known as an algorithm. A collection of computer programs, libraries and related data are referred to as a software.
- Process Control Block (PCB)- A Process Control Block is a data structure maintained by the Operating System for every process. The PCB is identified by an integer process ID (PID). A PCB keeps all the information needed to keep track of a process as listed below in the table.
- Schedulers- Schedulers are special system software which handle process scheduling in various ways. Their main task is to select the jobs to be submitted into the system and to decide which process to run.
- Long-Term Scheduler- A long-term scheduler is also called a job scheduler. A long-term scheduler determines which programs are admitted to the system for processing. Process loads into the memory for CPU scheduling.
- Short-Term Scheduler- Short Term Scheduler is also called as CPU scheduler. Short Term Scheduler main objective is to increase system performance in accordance with the chosen set of criteria. Short-term schedulers, also known as dispatchers, make the decision of which process to execute next. Short-term schedulers are faster than long-term schedulers.
- Medium-Term Scheduler- Medium-term scheduling is a part of swapping. A running process may become suspended if it makes an I/O request. A suspended processes cannot make any progress towards completion. In this condition, to remove the process from memory and make space for other processes, the suspended process is moved to the secondary storage. This process is called swapping, and the process is said to be swapped out or rolled out. Swapping may be necessary to improve the process mix.
- Context Switch- Context switching is an essential part of a multitasking operating system features.
- Virtual Memory- A computer can address more memory than the amount physically installed on the system. This extra memory is actually called virtual memory and it is a section of a hard disk that’s set up to emulate the computer’s RAM.
- I/O system- An I/O system is required to take an application I/O request and send it to the physical device, then take whatever response comes back from the device and send it to the application. I/O devices can be divided into two categories −
- Block devices − A block device is one with which the driver communicates by sending entire blocks of data. For example, Hard disks, USB cameras, Disk-On-Key etc.
- Character devices − A character device is one with which the driver communicates by sending and receiving single characters (bytes, octets). For example, serial ports, parallel ports, sounds cards etc.
- Device Controllers- Device drivers are software modules that can be plugged into an OS to handle a particular device. Operating System takes help from device drivers to handle all I/O devices. The Device Controller works like an interface between a device and a device driver. I/O units typically consist of a mechanical component and an electronic component where electronic component is called the device controller. There is always a device controller and a device driver for each device to communicate with the Operating Systems. A device controller may be able to handle multiple devices. As an interface its main task is to convert serial bit stream to block of bytes, perform error correction as necessary. Any device connected to the computer is connected by a plug and socket, and the socket is connected to a device controller.
Following is a model for connecting the CPU, memory, controllers, and I/O devices where CPU and device controllers all use a common bus for communication.
- Synchronous I/O − In this scheme CPU execution waits while I/O proceeds
- Asynchronous I/O − I/O proceeds concurrently with CPU execution.
A computer must have a way of detecting the arrival of any type of input. There are two ways that this can happen, known as polling and interrupts.
- Polling I/O- Polling is the simplest way for an I/O device to communicate with the processor.
- Interrupts I/O- An alternative scheme for dealing with I/O is the interrupt-driven method.
- Memory Management- Memory management is the functionality of an operating system which handles or manages primary memory and moves processes back and forth between main memory and disk during execution. Memory management keeps track of each and every memory location, regardless of either it is allocated to some process or it is free. Memory management checks how much memory is to be allocated to processes. Memory management decides which process will get memory at what time. Memory management tracks whenever some memory gets freed or unallocated and correspondingly it updates the status. The basic concepts related to Memory Management.
- Process Address Space- The process address space is the set of logical addresses that a process references in its code. The set of all logical addresses generated by a program is referred to as a logical address space. The set of all physical addresses corresponding to these logical addresses is referred to as a physical address space.
- Swapping- Swapping is a mechanism in which a process can be swapped temporarily out of main memory (or move) to secondary storage (disk) and make that memory available to other processes. At some later time, the system swaps back the process from the secondary storage to main memory.
- Fragmentation- As processes are loaded and removed from memory, the free memory space is broken into little pieces. It happens after sometimes that processes cannot be allocated to memory blocks considering their small size and memory blocks remains unused. This problem is known as Fragmentation.
- Paging- A computer can address more memory than the amount physically installed on the system. This extra memory is actually called virtual memory and it is a section of a hard that’s set up to emulate the computer’s RAM. Paging technique plays an important role in implementing virtual memory. Paging is a memory management technique in which process address space is broken into blocks of the same size called pages. Main memory is divided into small fixed-sized blocks of (physical) memory called frames and the size of a frame is kept the same as that of a page to have optimum utilization of the main memory and to avoid external fragmentation.
- Address Translation- Page address is called logical address and represented by page number and the offset.
- Logical Address = Page number + page offset
Frame address is called physical address and represented by a frame number and the offset. Physical Address = Frame number + page offset
A data structure called page map table is used to keep track of the relation between a page of a process to a frame in physical memory.
- Segmentation- Segmentation is a memory management technique in which each job is divided into several segments of different sizes, one for each module that contains pieces that perform related functions. Each segment is actually a different logical address space of the program.
- File- A file is a named collection of related information that is recorded on secondary storage such as magnetic disks, magnetic tapes and optical disks. A file is a sequence of bits, bytes, lines or records whose meaning is defined by the files creator and user.
- File Structure- A File Structure is according to a required format that the operating system can understand. A file has a certain defined structure according to its type. A text file is a sequence of characters organized into lines. A source file is a sequence of procedures and functions. An object file is a sequence of bytes organized into blocks that are understandable by the machine. When operating system defines different file structures, it also contains the code to support these file structure. Unix, MS-DOS support minimum number of file structure.
- File Type- File type refers to the ability of the operating system to distinguish different types of file such as text files source files and binary files etc. Many operating systems support many types of files. Operating system like MS-DOS and UNIX have the following types of files −
- Ordinary files- are the files that contain user information. These may have text, databases or executable program. The user can apply various operations on such files like add, modify, delete or even remove the entire file.
- Directory files- These files contain list of file names and other information related to these files.
- Special files- These files are also known as device files. These files represent physical device like disks, terminals, printers, networks, tape drive etc.
- File Access Mechanisms- File access mechanism refers to the manner in which the records of a file may be accessed. There are several ways to access files File Access Mechanisms. File access mechanism refers to the manner in which the records of a file may be accessed.
- Sequential access- A sequential access is that in which the records are accessed in some sequence, i.e., the information in the file is processed in order, one record after the other. This access method is the most primitive one.
- Direct/Random access- Random access file organization provides, accessing the records directly. Each record has its own address on the file with by the help of which it can be directly accessed for reading or writing. The records need not be in any sequence within the file and they need not be in adjacent locations on the storage medium.
- Indexed sequential access- This mechanism is built up on base of sequential access. An index is created for each file which contains pointers to various blocks. Index is searched sequentially and its pointer is used to access the file directly.
- Operating System – Security- Security refers to providing a protection system to computer system resources such as CPU, memory, disk, software programs and most importantly data/information stored in the computer system. If a computer program is run by an unauthorized user, then he/she may cause severe damage to computer or data stored in it.
- Program Threats-Operating system’s processes and kernel do the designated task as instructed. If a user program made these process do malicious tasks, then it is known as Program Threats.
Following is the list of some well-known program threats.
- Trojan Horse − Such program traps user login credentials and stores them to send to malicious user who can later on login to computer and can access system resources.
- Trap Door − If a program which is designed to work as required, have a security hole in its code and perform illegal action without knowledge of user then it is called to have a trap door.
- Logic Bomb − Logic bomb is a situation when a program misbehaves only when certain conditions met otherwise it works as a genuine program. It is harder to detect.
- Virus − Virus as name suggest can replicate themselves on computer system. They are highly dangerous and can modify/delete user files, crash systems. A virus is generatlly a small code embedded in a program. As user accesses the program, the virus starts getting embedded in other files/ programs and can make system unusable for user
- System Threats- System threats refers to misuse of system services and network connections to put user in trouble. System threats can be used to launch program threats on a complete network called as program attack. System threats creates such an environment that operating system resources/ user files are misused.
- Worm − Worm is a process which can choked down a system performance by using system resources to extreme levels. A Worm process generates its multiple copies where each copy uses system resources, prevents all other processes to get required resources. Worms processes can even shut down an entire network.
- Port Scanning − Port scanning is a mechanism or means by which a hacker can detects system vulnerabilities to make an attack on the system.
- Denial of Service − Denial of service attacks normally prevents user to make legitimate use of the system.
Unix
- Unix is an operating system. Unix supports multitasking and multi-user functionality.
- The Unix operating system is a set of programs that act as a link between the computer and the user.
- The computer programs that allocate the system resources and coordinate all the details of the computer’s internals is called the operating system or the kernel.
- Users communicate with the kernel through a program known as the shell.
- The shell is a command line interpreter; it translates commands entered by the user and converts them into a language that is understood by the kernel.
- Unix was originally developed in 1969 by a group of AT&T employees Ken Thompson, Dennis Ritchie, Douglas McIlroy, and Joe Ossanna at Bell Labs.
- There are various Unix variants available in the market. Solaris Unix, AIX, HP Unix and BSD are a few examples. Linux is also a flavor of Unix which is freely available.
- Several people can use a Unix computer at the same time; hence Unix is called a multiuser system.
- A user can also run multiple programs at the same time; hence Unix is a multitasking environment.
- Kernel − The kernel is the heart of the operating system. It interacts with the hardware and most of the tasks like memory management, task scheduling and file management.
- Shell − The shell is the utility that processes your requests. When you type in a command at your terminal, the shell interprets the command and calls the program that you want. The shell uses standard syntax for all commands. C Shell, Bourne Shell and Korn Shell are the most famous shells which are available with most of the Unix variants.
- Files and Directories − All the data of Unix is organized into files. All files are then organized into directories. These directories are further organized into a tree-like structure called the filesystem.
- Linux is one of popular version of UNIX operating System. It is open source as its source code is freely available. It is free to use. Linux was designed considering UNIX compatibility. Its functionality list is quite similar to that of UNIX.
MS-DOS
- Short for Microsoft Disk Operating System, MS-DOS is a non-graphical command line operating system created for IBM compatible computers. MS-DOS was first introduced by Microsoft in August 1981 and was last updated in 1994 with MS-DOS 6.22. The command shell commonly known as the Windows command line.
- MS-DOS is an operating system for x86-based personal computers developed by Microsoft.
- MS-DOS was the main operating system for IBM PC compatible personal computers during the 1980s.
- DOS exists in two forms. The one supplied for IBM Personal Computers is known as PC-DOS and other compatible personal computers use MS-DOS.
Booting Process in DOS
- Booting may be defined as process of loading the operating system into memory.
- The booting process starts from the moment when we power on computer and continues till moment, computer is ready for use.
- In the DOS, booting process starts when we start computer and continues till DOS prompt is displayed.
- The booting process of DOS mainly deals with loading three main system files of DOS into memory. These files are IO.SYS, MSDOS.SYS and COMMAND.COM.
- Once the computer system is turned on, BIOS (Basic Input /Output System) performs a series of activities or functionality test on programs stored in ROM, called on Power-on Self Test (POST) that checks to see whether peripherals in system are in perfect order or not.
- The BIOS is done with pre-boot activities or functionality test, it read bootable sequence from CMOS (Common Metal Oxide Semiconductor) and looks for master boot record in first physical sector of the bootable disk as per boot device sequence specified in CMOS.
- Master boot record will be searched first in a floppy disk drive. If not found, then hard disk drive will be searched for master boot record. But if the master boot record is not even present on hard disk, then CDROM drive will be searched. If the system is not able to read master boot record from any of these sources, ROM displays the message “No Boot device found” and system is halted. On finding master boot record from a particular bootable disk drive, operating system loader, also called Bootstrap loader is loaded from boot sector of that bootable drive· into memory. A bootstrap loader is a special program that is present in boot sector of bootable drive.
- Bootstrap loader first loads the IO.SYS file. After this, MSDOS.SYS file is loaded which is core file of DOS operating system.
- SYS file searches to find Command Interpreter in CONFIG.SYS file and when it finds, it loads into memory. If no Command Interpreter specified in the CONFIG.SYS file, the COMMAND.COM file is loaded as default Command Interpreter of DOS operating system.
- The last file is to be loaded and executed is the AUTOEXEC.BAT file that contains a sequence of DOS commands. After this, the prompt is displayed, and we can see drive letter of bootable drive displayed on the computer system, which indicates that operating system has been successfully on the system from that drive.
Types of Booting:
- Cold Booting/Switch Booting –When the user starts computer by pressing power switch on system unit, the operating system is loaded from disk to main memory this type of booting is called Cold Booting. This booting takes more time than Hot or Warm Booting.
- Hot or Warm Booting –Hot booting is done when computer system comes to no response state/hang state. Computer does not respond to commands supplied by user. There are many reasons for this state, only solution is to reboot computer by using the Reset button on cabinet or by pressing a combination of ALT + CTRL + DEL keys from keyboard.
- MS-DOS is a command-line operating system that allows you to perform various tasks according to given commands. Here some useful commands-
- cd : Change directory or display current directory path.
- cls : Clear the window.
- dir : Display list of contents of current directory.
- help : Display list of commands or help about a command.
- notepad : Run the Windows Notepad text editor.
- type : Displays the contents of a text file.
- assoc : Displays or modifies filename extension associations.
- attrib : Displays or changes file attributes.
- call : Calls one batch program file from another.
- chkdsk : Checks a disk and displays a status report.
- chkntfs : Displays or modifies the checking of disk at startup.
- color : Sets the text and background colors.
- comp : Compares the contents of two files or sets of files.
- copy : Copies one or more files to another location. See also: xcopy
- date : Displays or sets the computer’s date. See also: time
- del (or erase) : Deletes one or more files.
- defrag : Defragment the specified storage device.
- doskey : Display command history; define macros.
- echo : Displays messages, or turns command echoing on/off.
- edit : Runs the MS-DOS text editor. See also: notepad
- exit : Closes the MS-DOS window.
- fc : Compares two files or sets of files and displays the differences.
- find : Searches for a text string in a file or files.
- findstr : Search for a regular expression text string in a file or files.
- goto : Used in a batch program file to jump to a particular line.
- if : Used in a batch program file to perform conditional testing.
- md (or mkdir) : Creates a directory.
- more : Displays the contents of a file one screen at a time.
- move : Moves one or more files from one directory to another directory.
- rd (or rmdir) : Removes a directory.
- rem : Used in a batch program file to identify comments.
- ren (or rename) : Renames a file or files.
- sort : Sorts input.
- start : Starts a new window to run a specified program or command.
- time : Displays or sets the computer’s time. See also: date
- tree : Graphically displays the directory structure of a drive or directory.
- xcopy : Copies files and directory trees. See also: copy
The internet related commands
- arp : Displays ARP (address resolution protocol) translation tables.
- ftp : FTP (file transfer program) to transfer files to/from server.
- ipconfig : Displays internet configuration, including IP address.
- netsh : Network services shell.
- nslookup : Lookup IP address to/from domain name.
- netstat : Displays current TCP/IP network connections and statistics.
- ping : Ping the specified internet IP address or host name.
- telnet : Starts a text-based telnet session to the specified host.
- tftp : Transfers files to/from remote computer running TFTP service.
- tracert : Traces the route to the specified IP address or host.
The following command are third-parties. Some are equivalent to the Linux utility by the same name.
- config : Defragment one or more files (rather than entire drive).
- clip : Copy command output to Windows clipboard. See: paste
- du : Displays disk usage for selected files or directories.
- lynx : Text based web browser.
- paste : Paste Windows clipboard to command input. See: clip
- strings : Find all strings of a specified minimum length.
- whois : Lookup domain ownership information.
Windows
- The Windows operating system (Windows OS) is developed by Microsoft Corporation. The history of Windows OS is from 1985 to present day.
- Windows is a desktop operating system developed by Microsoft.
- Each version of Windows comes with a graphical user interface that includes a desktop with icons and a task bar that is displayed at the bottom of the screen by default.
- The Windows “File Explorer” allows users to open multiple windows, browse folders, and open files and applications.
- Windows Start menu, which provides quick access to files, settings, and the Windows search feature.
- The task bar at the bottom of the screen is an easy way to identify a Windows desktop.
- Windows is available in “Home” and “Pro” editions. The Home edition is sufficient for most users, while the Pro edition includes additional networking and administrative features useful in corporate workspaces.
- Windows runs on standard x86 hardware.
- Software programs written for Windows may be called apps, applications, or executable files.
- Regardless of their label, Windows software programs have an .EXE file extension.
- 64-bit versions of Windows run both 32 and 64-bit apps, while 32-bit versions only run 32-bit applications.
Control Panel
- The Control Panel is a component of Microsoft Windows that provides the ability to view and change system settings. It consists of a set of applets that include adding or removing hardware and software, controlling user accounts, changing accessibility options, and accessing networking settings. Additional applets are provided by third parties, such as audio and video drivers, VPN tools, input devices, and networking tools.
- Programs and Feature- This opens the Uninstall a Program applet. May be used to uninstall installed programs, or add or remove features from Windows
- Date and Time- Opens the Date and Time applet. Allows you to set date and time, change time zone, add additional clocks, and sync Internet time.
- Device Manager- The Device Manager lists all installed hardware. May be used to install and remove devices, install drivers, and more
- Display- provides you with options to set display related settings such as the color profile or scaling. Loads the Settings app on Windows 10.
- Firewall- Opens the Windows Firewall. Turn it on or off, and open the advanced settings to block or allow connections.
- Infrared- Lets you manage infrared devices.
- Internet Options- Opens the classic Internet Options window. Manage Internet settings that Internet Explorer and other browsers may use.
- Controllers- Manage game controllers connnected to the operating system
- Keyboard- Change keyboard repeat delay and rate, cursor blink rate, and check installed keyboard hardware.
- Language- control input.dll Opens the Language control panel applet. Add, remove or change the priority of languages.
- Mouse- The mouse controls enable you to change mouse icons, button behavior, wheel scrolling, and more.
- Network- Opens the Network and Sharing Center. May use it to add a new network, set up connections, and manage existing networks
- Network Connections- Lists all known network connections and their status.
- Power- Opens the Power Options. Set a power plan, and customize it.
- Region- The Region control panel applets lets you change date and time formats, and your location
- Screensaver- Opens the Screensaver dialog to enable, disable and configure screensavers.
- Sound- The Sound properties lists all playback and recording devices, options to configure those, and manage sounds and communications.
- System Properties- lists information about the device and Windows, and links to other control panel areas.
- Tablet PC- Only available if you run in tablet PC mode.
- Location Information– Set your country, area code, carrier code and dial number for telephony and modem services.
- Security and Maintenance- Manage Security and Maintenance related features
- User Accounts- Opens the list of user accounts on the system.
Internet And Networking
Internet
- Internet is a world-wide global system of interconnected computer networks. Internet uses the standard Internet Protocol (TCP/IP). Every computer in internet is identified by a unique IP address. IP Address is a unique set of numbers (such as 110.22.33.114) which identifies a computer location. A special computer DNS (Domain Name Server) is used to give name to the IP Address so that user can locate a computer by a name. For example, a DNS server will resolve a name https://www.ucidream.com to a particular IP address to uniquely identify the computer on which this website is hosted. Internet is accessible to every user all over the world.
- Internet Evolution
- The concept of Internet was originated in 1969 and has undergone several technological & Infrastructural changes as :
- The origin of Internet devised from the concept of Advanced Research Project Agency Network (ARPANET). ARPANET was developed by United States Department of Defense. Basic purpose of ARPANET was to provide communication among the various bodies of government. Initially, there were only four nodes, formally called Hosts. In 1972, the ARPANET spread over the globe with 23 nodes located at different countries and thus became known as Internet. By the time, with invention of new technologies such as TCP/IP protocols, DNS, WWW, browsers, scripting languages etc., Internet provided a medium to publish and access information over the web.
- Extranet
- Extranet refers to network within an organization, using internet to connect to the outsiders in controlled manner. It helps to connect businesses with their customers and suppliers and therefore allows working in a collaborative manner.
- Extranet vs Intranet
- Extranet- Internal network that can be accessed externally. Extranet is extension of company’s Intranet. For limited external communication between customers, suppliers and business partners.
- Intranet- Internal network that cannot be accessed externally. Only limited users of a company. Only for communication within a company.
Internet Models
OSI Reference Model
- OSI Reference Model- OSI is acronym of Open System Interface. This model is developed by the international organization of Standardization (ISO) and therefore also referred as ISO-OSI Model. The OSI model consists of seven layers. Each layer has a specific function; however, each layer provides services to the layer above.
- Physical Layer- The Physical layer is responsible for this type’s activities. Activating, maintaining and deactivating the physical connection. Defining voltages and data rates needed for transmission. Converting digital bits into electrical signal. Deciding whether the connection is simplex, half duplex or full duplex.
- Data Link Layer- The data link layer performs for these functions. Performs synchronization and error control for the information which is to be transmitted over the physical link. Enables error detection, and adds error detection bits to the data which are to be transmitted.
- Network Layer- These are the functions of Network Layer- To route the signals through various channels to the other end. To act as the network controller by deciding which route data should take. To divide the outgoing messages into packets and to assemble incoming packets into messages for higher levels.
- Transport Layer- The Transport layer performs for these functions. It decides if the data transmission should take place on parallel paths or single path. It performs multiplexing, splitting on the data. It breaks the data groups into smaller units so that they are handled more efficiently by the network layer. The Transport Layer guarantees transmission of data from one end to another end.
- Session Layer- The Session layer performs for these functions. Manages the messages and synchronizes conversations between two different applications. It controls logging on and off, user identification, billing and session management.
- Presentation Layer- This layer makes it sure that the information is delivered in such a form that the receiving system will understand and use it.
- Application Layer– The Application layer performs for these functions- It provides different services such as manipulation of information in several ways, retransferring the files of information, distributing the results etc. The functions such as LOGIN or password checking are also performed by the application layer.
TCP/IP Reference Model
- TCP/IP model is practical model and is used in the Internet. TCP/IP is acronym of Transmission Control Protocol and Internet Protocol. The TCP/IP model combines the two layers (Physical and Data link layer) into one layer i.e., Host-to-Network layer. The various layers of TCP/IP model:
- Application Layer- This layer is same as that of the OSI model and performs for these functions. It provides different services such as manipulation of information in several ways, retransferring the files of information, distributing the results etc. The functions such as LOGIN or password checking are also performed by the application layer.
- Protocols used: TELNET, FTP, SMTP, DN, HTTP, NNTP are the protocols employed in this layer.
- Transport Layer- It does the same functions as that of transport layer in OSI model. Here are the key points regarding transport layer. It uses TCP and UDP protocol for end-to-end transmission. TCP is reliable and connection-oriented protocol. TCP also handles flow control. The UDP is not reliable and a connection less protocol also does not perform flow control.
- Protocols used: TCP/IP and UDP protocols are employed in this layer.
- Internet Layer- The function of this layer is to allow the host to insert packets into network and then make them travel independently to the destination. However, the order of receiving the packet can be different from the sequence they were sent.
- Protocols used: Internet Protocol (IP) is employed in Internet layer.
- Host-to-Network Layer- This is the lowest layer in TCP/IP model. The host has to connect to network using some protocol, so that it can send IP packets over it. This protocol varies from host to host and network to network.
- Protocols used: ARPANET, SATNET, LAN, packet radio are the protocols which are used in this layer.
Domain Name System
- The Domain name system comprises of Domain Names, Domain Name Space, Name Server that have been described below:
- Domain Names– Domain Name is a symbolic string associated with an IP address. There are several domain names available; some of them are generic such as com, edu, gov, net etc, while some country level domain names such as au, in, za, us etc.
- The Generic Top-Level Domain names- Com-Commercial business, Edu- Education, Gov- U.S. government agency, Int+ International entity, Mil- U.S. military, Net- Networking organization, Org- Non profit organization
- The Country top-level domain names- Au- Australia, in – India, cl- Chile, fr- France, us- United States, za- South Africa, uk- United Kingdom, jp+ Japan, es- Spain, de- Germany, ca- Canada, ee- Estonia, hk- Hong Kong
- Domain Name Space- The domain name space refers a hierarchy in the internet naming structure. This hierarchy has multiple levels (from 0 to 127), with a root at the top.
- Name Server- Name server contains the DNS database. This database comprises of various names and their corresponding IP addresses. Since it is not possible for a single server to maintain entire DNS database, therefore, the information is distributed among many DNS servers. Hierarchy of server is same as hierarchy of names. The entire name space is divided into the zones
- Zones- Zone is collection of nodes (sub domains) under the main domain. The server maintains a database called zone file for every zone. The information about the nodes in the sub domain is stored in the servers at the lower levels however; the original server keeps reference to these lower levels of servers.
- Types of Name Servers- These are the three categories of Name Servers that manages the entire Domain Name System- Root Server, Primary Server and Secondary Server
- Root Server- Root Server is the top level server which consists of the entire DNS tree. It does not contain the information about domains but delegates the authority to the other server
- Primary Servers- Primary Server stores a file about its zone. It has authority to create, maintain, and update the zone file.
- Secondary Server- Secondary Server transfers complete information about a zone from another server which may be primary or secondary server. The secondary server does not have authority to create or update a zone file.
- DNS Working
- DNS translates the domain name into IP address automatically. Here the steps included in domain resolution process- 1. When we type www.ucidreamt.com into the browser, it asks the local DNS Server for its IP address. 2. Here the local DNS is at ISP end. 3. When the local DNS does not find the IP address of requested domain name, it forwards the request to the root DNS server and again enquires about IP address of it. 4. The root DNS server replies with delegation that I do not know the IP address of www.tutorialspoint.com but know the IP address of DNS Server. 5. The local DNS server then asks the com DNS Server the same question. 6. The com DNS Server replies the same that it does not know the IP address of www.tutorialspont.com but knows the address of tutorialspoint.com. 7. Then the local DNS asks the tutorialspoint.com DNS server the same question. 8. Then ucidream.com DNS server replies with IP address of www.ucidream.com. 9. Now, the local DNS sends the IP address of www.ucidream.com to the computer that sends the request.
Internet Services
- Communication Services- There are various Communication Services available that offer exchange of information with individuals or groups. These are various these services:
- Electronic Mail- Used to send electronic message over the internet.
- Telnet- Used to log on to a remote computer that is attached to internet.
- Newsgroup– Offers a forum for people to discuss topics of common interests.
- Internet Relay Chat (IRC)- Allows the people from all over the world to communicate in real time.
- Mailing Lists- Used to organize group of internet users to share common information through e-mail.
- Internet Telephony (VoIP)- Allows the internet users to talk across internet to any PC equipped to receive the call.
- Instant Messaging– Offers real time chat between individuals and group of people. Eg. Yahoo messenger, MSN messenger.
- Information Retrieval Services- There exist several Information retrieval services offering easy access to information present on the internet. These are various these services:
- File Transfer Protocol (FTP)- Enable the users to transfer files.
- Archie- It’s updated database of public FTP sites and their content. It helps to search a file by its name.
- Gopher- Used to search, retrieve, and display documents on remote sites.
- Very Easy Rodent Oriented Netwide Index to Computer Achieved (VERONICA)- VERONICA is gopher-based resource. It allows access to the information resource stored on gopher’s servers.
- Web Services- Web services allow exchange of information between applications on the web. Using web services, applications can easily interact with each other. The web services are offered using concept of Utility Computing.
- World Wide Web (WWW)- WWW is also known as W3. It offers a way to access documents spread over the several servers over the internet. These documents may contain texts, graphics, audio, video, hyperlinks. The hyperlinks allow the users to navigate between the documents.
- Video Conferencing- Video conferencing or Video teleconferencing is a method of communicating by two-way video and audio transmission with help of telecommunication technologies.
- Modes of Video Conferencing
- Point-to-Point- This mode of conferencing connects two locations only.
- Multi-point- This mode of conferencing connects more than two locations through Multi-point Control Unit (MCU).
Internet Protocols
- Transmission Control Protocol (TCP)- Transmission Control Protocol (TCP) corresponds to the Transport Layer of OSI Model. TCP is a reliable and connection-oriented protocol. TCP offers- Stream Data Transfer, Reliability, Efficient Flow Control, Full-duplex operation and Multiplexing. TCP offers connection oriented end-to-end packet delivery. TCP ensures reliability by sequencing bytes with a forwarding acknowledgement number that indicates to the destination the next byte the source expect to receive. It retransmits the bytes not acknowledged with in specified time period.
- Internet Protocol (IP)- Internet Protocol is connectionless and unreliable protocol. It ensures no guarantee of successfully transmission of data. In order to make it reliable, it must be paired with reliable protocol such as TCP at the transport layer.
- User Datagram Protocol (UDP)- Like IP, UDP is connectionless and unreliable protocol. It doesn’t require making a connection with the host to exchange data. Since UDP is unreliable protocol, there is no mechanism for ensuring that data sent is received. UDP transmits the data in form of a datagram.
- File Transfer Protocol (FTP)- FTP is used to copy files from one host to another. FTP offers the mechanism for the same in following manner:
- FTP creates two processes such as Control Process and Data Transfer Process at both ends i.e., at client as well as at server. FTP establishes two different connections: one is for data transfer and other is for control information. Control connection is made between control processes while Data Connection is made between<=”” b=””>. FTP uses port 21 for the control connection and Port 20 for the data connection.
- Trivial File Transfer Protocol (TFTP)- Trivial File Transfer Protocol is also used to transfer the files but it transfers the files without authentication. Unlike FTP, TFTP does not separate control and data information. Since there is no authentication exists, TFTP lacks in security features therefore it is not recommended to use TFTP. Key points- TFTP makes use of UDP for data transport. Each TFTP message is carried in separate UDP datagram. The first two bytes of a TFTP message specify the type of message. The TFTP session is initiated when a TFTP client sends a request to upload or download a file. The request is sent from an ephemeral UDP port to the UDP port 69 of an TFTP server.
- Telnet- Telnet is a protocol used to log in to remote computer on the internet. There are a number of Telnet clients having user friendly user interface.
- Hyper Text Transfer Protocol (HTTP)- HTTP is a communication protocol. It defines mechanism for communication between browser and the web server. It is also called request and response protocol because the communication between browser and server takes place in request and response pairs. HTTP Request- HTTP request comprises of lines which contains- Request line, Header Fields and Message body Key Points- The first line i.e. the Request line specifies the request method i.e. Get or Post. The second line specifies the header which indicates the domain name of the server from where index.htm is retrieved.
- HTTP Response- Like HTTP request, HTTP response also has certain structure. HTTP response contains- Status line, Headers and Message body
- Email is a service which allows us to send the message in electronic mode over the internet. It offers an efficient, inexpensive and real time mean of distributing information among people.
- E-mail Protocols
- SMPTP- SMTP stands for Simple Mail Transfer Protocol. It was first proposed in 1982. It is a standard protocol used for sending e-mail efficiently and reliably over the internet. Key Points– SMTP is application level protocol. SMTP is connection oriented protocol. SMTP is text based protocol. It handles exchange of messages between e-mail servers over TCP/IP network. Apart from transferring e-mail, SMPT also provides notification regarding incoming mail. When you send e-mail, your e-mail client sends it to your e-mail server which further contacts the recipient mail server using SMTP client. These SMTP commands specify the sender’s and receiver’s e-mail address, along with the message to be send. The exchange of commands between servers is carried out without intervention of any user. In case, message cannot be delivered, an error report is sent to the sender which makes SMTP a reliable protocol.
- IMAP- IMAP stands for Internet Message Access Protocol. It was first proposed in 1986. There exist five versions of IMAP as follows- Original IMAP, IMAP2, IMAP3, IMAP2bis and IMAP4 Key Points- IMAP allows the client program to manipulate the e-mail message on the server without downloading them on the local computer. The e-mail is hold and maintained by the remote server. It enables us to take any action such as downloading, delete the mail without reading the mail. It enables us to create, manipulate and delete remote message folders called mail boxes. IMAP enables the users to search the e-mails. It allows concurrent access to multiple mailboxes on multiple mail servers.
- POP- POP stands for Post Office Protocol. It is generally used to support a single client. There are several versions of POP but the POP 3 is the current standard.
- Key Points- POP is an application layer internet standard protocol. Since POP supports offline access to the messages, thus requires less internet usage time. POP does not allow search facility. In order to access the messaged, it is necessary to download them. It allows only one mailbox to be created on server. It is not suitable for accessing non mail data. POP commands are generally abbreviated into codes of three or four letters. Eg. STAT.
- E-mail Security
- E-mail Hacking- Email hacking can be done in any of the following ways- Spam, Virus and Phishing
- Spam- E-mail spamming is an act of sending Unsolicited Bulk E-mails (UBI) which one has not asked for. Email spams are the junk mails sent by commercial companies as an advertisement of their products and services.
- Virus– Some emails may incorporate with files containing malicious script which when run on your computer may lead to destroy your important data.
- Phishing- Email phishing is an activity of sending emails to a user claiming to be a legitimate enterprise. Its main purpose is to steal sensitive information such as usernames, passwords, and credit card details. Such emails contain link to websites that are infected with malware and direct the user to enter details at a fake website whose look and feels are same to legitimate one.
- E-mail Spamming and Junk Mails- Email spamming is an act of sending Unsolicited Bulk E-mails (UBI) which one has not asked for. Email spams are the junk mails sent by commercial companies as an advertisement of their products and services.
- Spams may cause the following problems- It floods your e-mail account with unwanted e-mails, which may result in loss of important e-mails if inbox is full. Time and energy is wasted in reviewing and deleting junk emails or spams. It consumes the bandwidth that slows the speed with which mails are delivered. Some unsolicited email may contain virus that can cause harm to your computer.
- E-mail Providers- There are several email service providers available in the market with their enabled features such as sending, receiving, drafting, storing an email and much more.
- The popular email service providers- Gmail, Hotmail, Yahoo Mail, iCloud Mail, ATM Mai, Mail.com and GMX Mail, Shortmail, Inbox.com, Facebook Messages, My Way Mail etc.
Website Designing
- Web designing has direct link to visual aspect of a web site. Effective web design is necessary to communicate ideas effectively. Web designing is subset of web development. However, these terms are used interchangeably.
- Wireframe- Wireframe refers to a visual guide to appearance of web pages. It helps to define structure of web site, linking between web pages and layout of visual elements.
Web development
- Web development refers to building website and deploying on the web. Web development requires use of scripting languages both at the server end as well as at client end.
- Web Development Process- Web development process includes all the steps that are good to take to build an attractive, effective and responsive website.
- Web development tools- Web development tools helps the developer to test and debug the web sites. Now a days the web development tooll come with the web browsers as add-ons. All web browsers have built in tools for this purpose. These tools allow the web developer to use HTML, CSS and JavaScript etc.. These are accessed by hovering over an item on a web page and selecting the “Inspect Element” from the context menu.
- Featues- Following are the common featuers that every web development tool exhibits:
- HTML and the DOM- HTML and DOM viewer allows you to see the DOM as it was rendered. It also allows to make changes to HTML and DOM and see the changes reflected in the page after the change is made.
Websites Hosting
- Web hosting is a service of providing online space for storage of web pages. These web pages are made available via World Wide Web. The companies which offer website hosting are known as Web hosts. The servers on which web site is hosted remain switched on 24 x7. These servers are run by web hosting companies. Each server has its own IP address. Since IP addresses are difficult to remember therefore, webmaster points their domain name to the IP address of the server their website is stored on. It is not possible to host your website on your local computer, to do so you would have to leave your computer on 24 hours a day. This is not practical and cheaper as well. This is where web hosting companies comes in. Types of Hosting availed as per the need-
- Shared Hosting- In shared hosting, the hosting company puts thousand of website on the same physical server. Each customer has their own allocation of physical web space and a set of bandwidth limit. As all websites share same physical memory, MYSQL server and Apache server, one website on the server experiencing high traffic load will affect performance of all websites on the server.
- Virtual Private Server (VPS)- It is also known as Virtual Dedicated Server. It is a server which is partitioned into smaller servers. In this customer is given their own partition, which is installed with its own operating system. Unlike shared hosting, VPS doesn’t share memory or processor time rather it allocates certain amount of memory and CPU to use which means that any problem on a VPS partition on the same drive will not affect other VPS customers.
- Dedicated Server– In this kind of hosting, single dedicated server is setup for just one customer. It is commonly used by the businesses that need the power, control and security that a dedicated server offers.
- Reseller Hosting- A reseller acts as a middle man and sells hosting space of someone else’s server.
- Grid Hosting– Instead of utilizing one server, Grid Hosting spreads resources over a large number of servers. It is quite stable and flexible. The servers can be added or taken away from the grid without crashing the system.
World Wide Web
- A technical definition of the World Wide Web is: all the resources and users on the Internet that are using the Hypertext Transfer Protocol (HTTP). A broader definition comes from the organization that Web inventor Tim Berners-Lee helped found, the World Wide Web Consortium (W3C). The World Wide Web is the universe of network-accessible information, an embodiment of human knowledge. In simple terms, The World Wide Web is a way of exchanging information between computers on the Internet, tying them together into a vast collection of interactive multimedia resources. Internet and Web is not the same thing: Web uses internet to pass over the information.
- WWW Evolution– World Wide Web was created by Timothy Berners Lee in 1989 at CERN in Geneva. World Wide Web came into existence as a proposal by him, to allow researchers to work together effectively and efficiently at CERN. Eventually it became World Wide Web.
- Identifiers and Character Set- Uniform Resource Identifier (URI) is used to uniquely identify resources on the web and UNICODE makes it possible to built web pages that can be read and write in human languages.
- Data Interchange- Resource Description Framework (RDF) framework helps in defining core representation of data for web. RDF represents data about resource in graph form.
- Taxonomies- RDF Schema (RDFS) allows more standardized description of taxonomies and other ontological constructs.
- Ontologies- Web Ontology Language (OWL) offers more constructs over RDFS. It comes in following three versions- OWL Lite for taxonomies and simple constraints. OWL DL for full description logic support. OWL for more syntactic freedom of RDF
- Rules- RIF and SWRL offers rules beyond the constructs that are available from RDFs and OWL. Simple Protocol and RDF Query Language (SPARQL) is SQL like language used for querying RDF data and OWL Ontologies.
- Proof- All semantic and rules that are executed at layers below Proof and their result will be used to prove deductions.
- Cryptography- Cryptography means such as digital signature for verification of the origin of sources is used.
- WWW Operation- WWW works on client- server approach. Here explains how the web works: User enters the URL (say, https://www.ucidream.com) of the web page in the address bar of web browser. Then browser requests the Domain Name Server for the IP address corresponding to www.ucidream.com. After receiving IP address, browser sends the request for web page to the web server using HTTP protocol which specifies the way the browser and web server communicates. Then web server receives request using HTTP protocol and checks its search for the requested web page. If found it returns it back to the web browser and close the HTTP connection. Now the web browser receives the web page, It interprets it and display the contents of web page in web browser’s window.
- Web Browsers
- web Browser is an application software that allows us to view and explore information on the web. User can request for any web page by just entering a URL into address bar. Web browser can show text, audio, video, animation and more. It is the responsibility of a web browser to interpret text and commands contained in the web page. Earlier the web browsers were text-based while now a days graphical-based or voice-based web browsers are also available. Web browser available today- Internet Explorer, Google Chrome, Mozilla Firefox, Netscape Navigator, Opera, Safari, Sea Monkey, K-meleon.
Web Server
- Web server is a computer where the web content is stored. y web server is used to host the web sites but there exist other web servers also such as gaming, storage, FTP, email etc. Web site is collection of web pages while web server is a software that respond to the request for web resources.
- Web Server Working- Web server respond to the client request in either of the following two ways- Sending the file to the client associated with the requested URL. Generating response by invoking a script and communicating with database
- Key Points- When client sends request for a web page, the web server search for the requested page if requested page is found then it will send it to client with an HTTP response. If the requested web page is not found, web server will the send an HTTP response: Error 404 Not found. If client has requested for some other resources, then the web server will contact to the application server and data store to construct the HTTP response.
- Architecture- Web Server Architecture follows the following two approaches:
- Concurrent Approach– Concurrent approach allows the web server to handle multiple client requests at the same time. It can be achieved by following methods:
- Multi-processing- In this a single process (parent process) initiates several single-threaded child processes and distribute incoming requests to these child processes. Each of the child processes are responsible for handling single request. It is the responsibility of parent process to monitor the load and decide if processes should be killed or forked.
- Multi-threaded– Unlike Multi-process, it creates multiple single-threaded process.
- Hybrid- It is combination of above two approaches. In this approach multiple process are created and each process initiates multiple threads. Each of the threads handles one connection. Using multiple threads in single process results in less load on system resources.
Proxy Server
- Proxy server is an intermediary server between client and the internet. Proxy servers offers the following basic functionalities- Firewall and network data filtering. Network connection sharing. Data caching. Proxy servers allow to hide, conceal and make your network id anonymous by hiding your IP address.
- Purpose of Proxy Servers– Following are the reasons to use proxy servers- Monitoring and Filtering, Improving performance, Translation, Accessing services anonymously and Security.
- Type of Proxies:
- Forward Proxies- In this the client requests its internal network server to forward to the internet.
- Open Proxies- Open Proxies helps the clients to conceal their IP address while browsing the web.
- Reverse Proxies- In this the requests are forwarded to one or more proxy servers and the response from the proxy server is retrieved as if it came directly from the original Server.
- Proxy server listener- It is the port where new request from the client browser is listened. This module also performs blocking of clients from the list given by the user.
- Connection Manager- It contains the main functionality of the proxy server. It performs the following functions:
- It contains the main functionality of the proxy server. It performs the following functions- Read request from header of the client., Parse the URL and determine whether the URL is blocked or not, Generate connection to the web server, Read the reply from the web server, If no copy of page is found in the cache then download the page from web server else will check its last modified date from the reply header and accordingly will read from the cache or server from the web, Then it will also check whether caching is allowed or not and accordingly will cache the page.
- Cache Manager- This module is responsible for storing, deleting, clearing and searching of web pages in the cache.
- Log Manager- This module is responsible for viewing, clearing and updating the logs.
- Configuration– This module helps to create configuration settings which in turn let other modules to perform desired configurations such as caching.
Search Engines
- Search Engine refers to a huge database of internet resources such as web pages, newsgroups, programs, images etc. It helps to locate information on World Wide Web. User can search for any information by passing query in form of keywords or phrase. It then searches for relevant information in its database and return to the user.
- Search Engine Components-There are three basic components of a search engine Web Crawler, Database and Search Interfaces
- Web crawler– It is also known as spider or bots. It is a software component that traverses the web to gather information.
- Database- All the information on the web is stored in database. It consists of huge web resources.
- Search Interfaces- This component is an interface between user and the database. It helps the user to search through the database.
- Internet Collaboration
- Online Chatting- Online chatting is a text-based communication between two or more people over the network. In this, the text message is delivered in real time and people get immediate response. Talkomatic was the world first online chat system. It was developed by Doug Brown and David R. Woolley in 1973.
- Instant Messaging (IM)- Instant messaging is a software utility that allows IM users to communicate by sending text messages, files, and images.
- Internet Relay Chat (IRC)- Internet Relay Chat is a protocol developed by Oikarinen in August 1988. It defines set of rules for communication between client and server by some communication mechanism such as chat rooms, over the internet. IRC consist of separate networks of IRC servers and machines. These allow IRC clients to connect to IRC. IRC client runs a program client to connect to a server on one of the IRC nets. After connecting to IRC server on IRC network, user can join with one or more channels and converse over there.
- Video Conferencing- Video conferencing or Video teleconferencing is a method of communicating by two-way video and audio transmission with help of telecommunication technologies.
- Modes of Video Conferencing
- Point-to-Point- This mode of conferencing connects two locations only.
- Multi-point- This mode of conferencing connects more than two locations through Multi-point Control Unit (MCU).
- Video Sharing- Video sharing is an IP Multimedia System (IMS) service that allows user to switch voice calls to unidirectional video streaming session. The video streaming session can be initiated by any of the parties. Moreover, the video source can be the camera or the pre-recorded video clip.
Mailing List
- In order to send same email to a group of people, an electron list is created which is know as Mailing List. It is the list server which receives and distributes postings and automatically manages subscriptions. Mailing list offers a forum, where users from all over the globe can answer questions and have them answered by others with shared interests.
- Types of Mailing List- The various types of mailing lists:
- Response List- It contains the group of people who have responsed to an offer in some way. These people are the customers who have shown interest in specific product or service.
- Compiled List- The compiled list is prepared by collecting information from various sources such as surveys, telemarketing etc.
- Announcements- These lists are created for sending out coupans , new product announcements and other offers to the customers.
- Discussion List- This list is created for sharing views on a specific topic suchas computer, environment, health, education etc.
Usenet (USEr NETwork)
- Like mailing lists Usenet is also a way of sharing information. It was started by Tom Truscott and Jim Ellis in 1979. Initially it was limited to two sites but today there are thousands of Usenet sites involving millions of people. Usenet is a kind of discussion group where people can share views on topic of their interest. The article posted to a newsgroup becomes available to all readers of the newsgroup.