Theory Assignment2014-15Submitted To:Submitted By:ChairpersonTomal KarmakarUSOLPGDCAPanjab University,Roll no: 31011Chandigarh

Paper: P.G.D-01Question 1: What is DOS? Explain the major features of DOS.

Answer: Operating system is an interface between the user and the computer. It is the minimum essential software that must be present on the computer in order to operate it. MS DOS is a single user operating system which allows the users to enter commands using textual interface. It controls the basic hardware components of the computer.

Features of DOS:1. The commands typed by the user at the DOS prompt are interpreted by DOS and the appropriate action is taken.2. It controls the way various applications operate with your computer. DOS creates an environment to let these applications talk to the computer hardware.3. User can set systems clock setting by DATE and TIME commands.4. It provides the facility to create and edit files/directories.5. It provides various file and disk management commands.

Question 2: Differentiate between RAM and ROM. Also distinguish betweenPROM and EPROM.

Answer: RAM (Random Access Memory):

The primary storage is referred to as random access memory. It takes same time to any address of the memory as the first address. It is also called read/write memory. It is volatile in nature as the storage of data and instructions inside the primary storage is temporary and lost on failure of power supply.

Types of RAM:

Synchronous DRAM (SDRAM):The Synchronous DRAM or SDRAM is tied to the system clock. SDRAM accomplishes its faster access using a number of internal performance improvements,

Double Data Rate SDRAM (DDR SDRAM): DDR SDRAM is similar in function to regular SDRAM but doubles the bandwidth of the memory by transferring data twice per cycle on both the rising and falling edges of the clock signal.

Direct Rambus DRAM (DRDRAM): DRDRAM works more like an internal bus than a conventional memory subsystem.

Synchronous-Link DRAM (SLDRAM) :SLDRAM greatly improves the performance of the memory subsystem over SDRAM.

ROM (READ ONLY MEMORY):

It is the ICs inside the PC that form the ROM. The storage of program and data in the ROM is permanent. The ROM can only read by the CPU but it cannot be changed. It is non volatile in nature as they do not lose their content on failure of power supply.

Some Important Types of ROM:

PROM (Programmable Read Only Memory): Once the programs are written it cannot changed and remain intact even if power is switched off. Therefore programs or instructions written in PROM or ROM cannot be erased or changed.

EPROM (Erasable Programmable Read Only Memory): EPROM chip can be reprogrammed time and again by erasing the information stored earlier in it by exposing the chip for some time ultraviolet light.

Question 3: What do you mean by seek time, latency time and access time?

Answer: Seek Time: It is one of the several delays associated with reading or writing data on a computers drive. This process is known as seeking and the time it takes for the head to move to move to the right place is the seek time.

Latency Time: The time between initiating a request for data and the beginning of the actual data transfer. On a disk, latency is the time it takes for the selected sector to come around and be positioned under the read/write head.

Disk Access Time: It is an average of the time between initiating a request and obtaining the first data character. It includes the command processing, theaverage seek time and average latency. Fast hard disks have access times of 10 milliseconds (ms) or less.

Question 4: Discuss the functioning of a computer system with the help of a block diagram.

Answer: A computer consist of an input unit, an output unit, memory unit, control unit and arithmetic logic unit (ALU). The control unit and ALU together are known as Central Processing Unit (CPU).

Bock Diagram of Computer:

(INFORMATION (DATA)) (OUTPUT) (PROGRAM AND DATA) (INPUT) (ARITHMETIC AND LOGICAL UNIT) (CONTROL UNIT) ( MEMORY)

CPU(Central Processing Unit)

Input Unit: It accepts the instructions and data from the outside world and supplies to the computer system for further processing.

CPU: The CPU is the brain of a computer system.

The CPU is also responsible for activating and controlling the operations of other units of the computer system.

Memory: It is a temporary storage area, which is built into the computer hardware and in which the instructions and data of the program resides, mainly when the program is being executed.

Control Unit: It manages and coordinates the entire computer system including the input and output units. It obtains instructions stored in the main memory, interprets the instructions and issue signals which causes other units of the system to execute them.

Arithmetic and Logical unit: It involves the arithmetic operations like addition, subtraction, multiplication, division and logic operation such as less than, greater than, equal to.

Output Unit: It accepts the results produced by the computer and supplies to the outside world.

Question 5: How negative numbers are represented in memory?

Answer: There are four systems for representing negative numbers in digital computer:

1. Signed magnitude: The leftmost bit is known as sign bit and it is used to demote the sign of the number. 0 indicates positive number or+ sign and 1 indicates negative number or sign.Example: 00000110 denotes +6 10000110 denotes -6 11111111 denotes -127 01111111 denotes +127

2. Ones complement: In this system also the leftmost bit is used as sign bit with 0 for plus and 1 for minus sign. To get ones complement of a binary number, replace each 1 by 0 and each 0 by 1 including the sign bit.Example:00000110+6 11111001-6 in ones complement 11111111+127 01111111-127 in ones complement

3. Twos complement: The leftmost bit is the sign bit with 0 for plus and 1 for minus. To negate a number a) each 1 is replaced by a 0 and each 0 by 1 and b) 1 is added to the resultExample: To represent -6 in 2s complement form 00000110(+6) 11111001-6 in 1s complement form 11111010-6 in 2s complement form If a carry occurs from the leftmost bit, it is neglected.

4. Excess 2m-1 for m-bit numbers: A number is represented by storing it as the sum of itself and 2m-1. For example, for 8 bit number, m=8 and the system is called excess 128 and the number is stored as its true value plus 128. For example, -3 is stored as -3+128=125=(01111101)2

Question 6: Highlight the features of Windows Operating System.

Answer: Features of Windows Operating System:

1. Windows 98 or windows 2000 or windows XP is pre-empting, multitasking, multithreaded operating system.2. It provides graphical user interface and also allows the user to work with Disk Operating System (DOS) and applications developed using DOS.3. Supports long file names that can contain up-to 255 characters including space and other special characters.4. Supports the new plug and play standard that allows you to simply plug a new card into your computer without having to set switches or other settings.5. Dynamic Data Exchange/Object Linking and Embedding (DDE/OLE) are methods for sharing data between documents. OLE is just cut and paste but allows incorporate graphs, charts, music, video, clipart and so on into your document.6. Remote Procedure Calls (RPCs) provide a way to work with a computer on a network. All the computers on the network may use the same application such as a database program.

Question 7: Write the features of vi editor.

Answer: Features of vi editor:

1. vi demands certain level of maturity and knowledge.

2. vi offers all the conventional editing functions.

3. The screen is uninformative.

4. Errors sing bells.

5. The same keys have multiple users.

6. We can make charts and tables using key combinations.

7. vi is case sensitive.

8. vi is an integral part of Unix.

9. Powerful undo features are available.

10. vi stores all changes in a editing buffer and finally saved into a file on disk when the user quits.

Question 8: Explain the different types of interrupts. How are they handled?

Answer: Interrupts are the programs which stop the normal program.

Types of Interrupts: In the 8085 microprocessor, there are thirteen Interrupts. There are five Hardware interrupts and eight Software Interrupts.

Hardware Interrupt:

These are of five types: TRAP, RST 7.5, RST 6.5, RST 5.5 and INTR.

Name

Priority

Address Branched to when Interrupted

TRAP

1 (Highest)

4.5*8=36=24H

RST 7.5

2

7.5*8=60=3CH

RST 6.5

3

6.5*8=52=34H

RST 5.5

4

5.5*8=44=2CH

INTR

5 (Lowest)

Table: Interrupt Priority

Software Interrupts: These are software instructions that cause an interrupt when they are executed. They are of eight types:

Software Interrupt

Vector Address

RST 0

0*8=00=00h

RST 1

1*8=08=08h

RST 2

2*8=16=10h

RST 3

3*8=24=18h

RST 4

4*8=32=20h

RST 5

5*8=40=28h

RST 6

6*8=48=30h

RST 7

7*8=56=38h

Address for Software Interrupts

Here RST stands for RESTART.

There are two ways to service, or act on the events that happen in the system. One is to scan or poll them and the other is to use interrupts.

Scanning is that each possible event is scanned in sequence, one at a time. Interrupts, on the other hand, cause the current process to be suspended temporarily and the event that caused the interrupt is serviced, or handled, immediately. The routine that is executed as a result of an interrupt is called the Interrupt Service Routine (ISR), or the Interrupt Handler Routine.

(START)The Instruction Cycle (when interrupt occurs) can be shown by means of a flowchart.

(Check for Interrupt Process Interrupt) (HALT) (Execute Instruction) (Fetch Next Instruction)

The microprocessor fetches the next instruction of the program, decodes it and then executes the instruction. If there was no interrupt then the instruction cycle would have come to a halt but if there is an interrupt, the Interrupt Enable signal is enabled or set and the interrupt process takes place. Microprocessor repeats the process of fetch, decode and execute till the end of the interrupt subroutine. Then the interrupt is disabled and processor returns back to its normal program.

Question 10: List out the reasons for the popularity of Unix.

Answer: Reasons for the popularity and success of the Unix System:

1. Portability: The system is written in a high level language. It is easy to read, understand, change and move to other machines.

2. Unix is a multiuser, multi tasking, time sharing and multi processing operating system.

3. The first system in C was 20 to 40 percent larger and slower but the advantages outweigh the disadvantages.

4. It has a simpler user interface that has the power to provide the service that users want.

5. It provides primitives that permit complex programs to be built from simpler programs.

6. It uses a hierarchical file system that allows easy maintenance and efficient implementation.

7. It uses a consistent format for files; the byte stream making application programs easier to write.

8. It provides a simple, consistent interface to peripheral devices.

9. Powerful System Security

10. Efficient System Communication

Paper: P.G.D-02Sub: DBMS Using SQL

Question 1: Compare the three models with respect to complexity and storage structure.

Answer: With respect to Storage Structure:Hierarchical Model in implemented by using hierarchical files, which preserve the hierarchical sequence of the database. In case of Relational Model, each relation is implemented as a separate file. Network model is usually implemented by using pointers and circularly linked lists (ring files).

With respect to Complexity:Hierarchical Model is comparatively less complex than network model but more complex than relational model. Relational Model is the simplest of all models. Network Model is highly complex and the source of its complexity lies in the data structure and the associated operations possible on this data structure.

Question 2: List the steps for designing the relational database for a given application.

Answer: Steps for designing the relational database:

1. Requirement collection and analysis: Requirement is typically given in sentences, which gives the descriptions of what the system should do or represent.

2. Conceptual Design:Database conceptual modelling attempts to represent requirements in a more rigorous, clear and operational way. It is also known as semantic modelling.

3. Logical Design:

a) One to One relationships: Merge the two entities into a single RDBMS table keeping all the attributes into it.

b) One to Many relationships: Create two RDBMS tables one for each entity. Add the primary key from the entity on one side to the entity on many side and identify it as foreign key.

c) Many to Many relationships: Create a new table and post the primary keys from both entities as attributes in the new table. The posted attributes are foreign keys.

4. Physical Design:This refers to all final Structured Query Language (SQL) commands, which will be used to create RDMS tables. It is system specific as different RDBMS might be used on different systems.

Question 3: List key features of PL/SQL.

Answer: Key features of PL/SQL:

Programming can declare variables to be used during statement processing.

Programmers can use error-handling routines to prevent programs from aborting unexpectedly.

Programmers can write interactive programs that accept input from the user.

Programmers can write interactive programs that accept input from the user.

Programmers can divide functions into logical blocks of code. Modular programming techniques support flexibility during the application development.

SQL statements can be processed simultaneously for better overall performances.

Question 4: What is difference between physical and logical data independence?

Answer: Logical data independence: It indicates that the conceptual schema can be changed without affecting the existing external schemas. The mapping between the external and conceptual levels would absorb the change. Logical data independence also insulates application programs from operations such as combining two records into one or splitting an existing record into two or more records.

Physical data independence: It indicates that the physical storage structures or devices used for storing the data could be changed without necessitating a change in the conceptual view or any of the external views. The mapping between the conceptual and internal levels would absorb the change.

It is achieved by the presence of the internal level of the database and the mapping from conceptual level of the database to the internal level.

Question 5: Explain the concept of distributed databases. Why are they better than centralised databases?

Answer: In centralised database system, the DBMS and the data reside at a single location and control as well as processing is limited to this location. The excessive load on the system at the central site would cause all the accesses to be delayed and failure of the communication link lead to the total disruption of the system.In the distributed database system, the database is stored on several computers. The computers in a distributed system communicate with each other through various communication media, such as high-speed networks or telephone lines. Because the database is distributed, different users can access it without interfering with one another.

Site ASite C

Communication via Site B Network

Question 6: State and explain the important characteristics of a relation.

Answer: The number of attributes in a given relation or equivalently the number of underlying domains is called the degree of a relation. A relation of degree one is said to be unary, a relation of degree two binary....and a relation of degree n is called n-ary. The suppliers relation S in table has degree equal to 3. The number of tuples in a relation at a given point of time is called cardinality of the relation.

Table 1:

S#

SNAME

CITY

STATUS

S1

IBM

Delhi

20

S2

HP

Bombay

10

S3

GODREJ

Pune

22

S4

SAMSUNG

Chandigarh

33

S5

LG

Delhi

20

S6

ACER

Bombay

10

Tuples

Relations possess certain characteristics:

There are no duplicate tuples: This first property illustrates the point that a relation and a table are not the same thing because a table might contain duplicate rows, whereas a relation cannot contain any duplicate tuples.

Tuples are unordered (top to bottom): This property follows from the fact that the body of the relation is a mathematical set and sets in mathematics are not ordered. In other words, there is no concept of positional addressing and there is no concept of nextness.

Attributes are unordered (left to right): For example, the attributes of relation S could just as well have been shown in the order SNAME, CITY, STATUS, S# and it would still have been the same relation. Thus, there is no such thing as the first attribute or the second attribute (etc.) and there is no next attribute. In other words, attributes are always referenced by name, never by position.

All attribute values are atomic: This property is a consequence of the fact that all underlying domains contain atomic values only. At every row and column position within the table, there is always exactly one value, never a collection of several values. Relations do not contain repeating groups.

Question 7: What is Database security? Why it is important for organisation?

Answer: Database security is a crucial issue in the database management system as it contain important information which is very valuable and sensitive for an organisation database. Security in database involves both policies and mechanism to protect the data from unauthorised access.Some database security threats: -- Data tampering -- Eavesdropping and data theft -- Falsifying users identities -- Password related threatsFour kinds of counter measures can be implemented: -- Access control -- Inference control -- Flow control -- Encryption

Question 7: Explain the different recovery techniques.

Answer: Restore/Rerun:

simplest form of recovery- no DB change log required

reload must recent backup & all transactions which have been processed since that time are rerun

time required to reprocess/no new processing until complete

not usually used unless as last resort

Rollback Recovery:

used to Undo transactions that have been processed to return DB to a correct state

used after deadlock or if transaction is aborted/abnormally terminated

uses Before-images & transaction log to return DB to most recent checkpoint

reprocess from that checkpoint making sure that problem does not recur

Rollforward Recovery:

Reload most recent Backup & then apply After images to the database until the most recent checkpoint is reached

used after system failure/DB destruction etc.

uses Backup, Transaction log & After-images to return DB to most recent checkpoint

Question 9: List the three major parts of a PL/SQL statement.

Answer: PL/SQL is a block structured language. Within a PL/SQL block of code, processes such as data manipulation or queries can occur.

The DECLARE section contains the definitions of variables and other objects such as constants and cursors. This section is the only mandatory part of PL/SQL block.

The PRPCEDURE section contains conditional commands and SQL statements and is where the block is controlled. This section is the only mandatory part of a PL/SQL block.

The EXECUTION section tells the PL/SQL block how to handle specified errors and user defined exceptions. This section is an optional part of a PL/SQL block.

Question10: List the commands that are associated with cursor control.

Answer: Basic cursor control commands: DECLARE, OPEN, FETCH and CLOSE.

DECLARE: The DECLARE statement belongs in the list of cursor control commands.

OPEN: Syntax BEGIN open employee_cursor; statement 1; statement 2; . . . END

FETCH: It populates a variable with values from a cursor. Example, INPUT:

DECLARE cursor employee_cursor is select emp_id, emp_name from employee; employee_record employee_cursor% ROWTYPE; BEGIN open employee_cursor; loop fetch employee_cursor into employee_record; end loop; close employee_cursor; END

CLOSE: When you have finished using a cursor in a block, you should close the cursor. SYNTAX: BEGIN open employee_cursor; statement 1; statement 2; . . . close employee_cursor; END

Paper: P.G.D-03Sub: Computer Based Accounting

Question 1: Explain the features of Tally.

Answer: The features of Tally:

Popular Package: Tally is one of the most popular accounting packages, which has almost 80,000 users all over the world and is still growing.

Easy to Use: Tally provides user friendly interface and hence is easy to use. Tally is based on the concept of no accounting codes concept.

Provides Complete Business Solution: The package comprises financial accounting and book keeping, inventory accounting and various tools for extracting, interpreting and presenting data to assist in the management of the business.

Available on Multi Platform: Tally is available on Windows 95, 98, ME 2000, NT. It will run on a standalone PC or network.

Question 2: What do you mean by subsidiary books? Explain the utility and functions of each of these books.

Answer: Subsidiary books keep all the transactions of similar nature are recorded at one place and that too in chronological order.Important Subsidiary Books and their functions:

Cashbook: It records all cash receipts and payments along with discount allowed and discount received.

Purchase Book: It records transactions relating to the goods purchased on credit.

Purchase Return Book: It records transactions relating to the return of goods to supplier.

Sales Book: It record transactions relating to goods sold on credit.

Sales Return Book: It records transaction relating to goods returned by the customers.

Bills Receivable Book: It records details regarding Bills Receivable.

Bills Payable Book: It records details regarding Bills Payable.

Journal Proper: It records all such transaction for which no separately subsidiary book is kept.

Question 3: What are the functions of accounting? Explain the importance of accounting.

Answer: Accounting is a service activity. Accounting includes several branches, e.g. financial accounting, managerial accounting and government accounting.

Functions of Accounting:

1. Recording: The basic function of accounting is recording the monetary aspects of all the transactions of business in an orderly manner for the purpose of memory and future reference.

2. Classifying: After the transactions have been recorded in the subsidiary books, these are classified and posted to the main book of account known as ledger.

3. Summarizing: The transactions recorded in the recorded in the ledger are summarized aid the balance in each account 1s ascertained and list of such balances called Trail Balance

4. Dealing with financial transactions: Accounting deals with only those transactions, which are of a financial character. Transactions, which are not of a financial character, are not recorded in the books of accounts.

5. Interpreting: The final stage in the accounting process is the analysis and interpretation of the financial data contained in the balance sheet and the Profit and Loss Account.

Objectives of Accounting:

To keep systematic record: The primary aim of accounting is to keep systematic records of business transactions.

To facilitate rational decision making: Accounting facilitates the task of decision making through the collection analysis and reporting of information.

Basis of Information System: Accounting is the basis of information system for collecting and communicating economic information about the business enterprise.

To ascertain the profit or loss at the end of a period: To know whether in a particular period the firm earned a profit or suffered a loss a statement known as income statement or profit and loss account is prepared.

To know the financial health of the business: For this purpose a statement known as balance sheet is prepared which records the assets and liabilities and represents the solvency of the firm.

Question 4: How do you post (a) Compound Entries (b) Opening Entry?

Answer: Posting of Compound Entry: In this, either there is one debit or there are more than one credit. More than one transaction are recorded by passing only one entry. Every debit must have the equal corresponding credit i.e. there may be only one debit element but many corresponding credit elements of equal value for vice versa.

Posting of Opening Entry: The entry made from the balances brought from the balances brought from previous year is known as the opening entry. The words To balance brought down or brought forward to the debit side and By balance brought down or forward to the credit side are written. In this amount of Capital is generally not given but this is difference between total debit balances and total credit balances given in the question.

Question 5: What is the meaning of bad debts? Why is it necessary to make provision for bad debts?

Answer: Bad debts mean the amount which is lost because a customer fails to pay. When a bad debt occurs, bad debts account is debited and customer account is credited, thus closing the account of the customer.Bad debts account being a loss is transferred to profit and loss account. Some business houses make provision to meet bad debts, which may occur in future. This is done by debiting the profit and loss account and crediting the provision for bad and doubtful debts account. The profit of the year is reduced by the amount of the provision for bad and doubtful debts, while preparing the balancing sheet; the amount of provision is deducted from the sundry debtors.

Question 6: What do you mean by Computerised Accounting? Why it is needed?

Answer: Computerised Accounting is a processing function, which involves, replacing the manual system of maintaining the books of accounts with the use of software package for accounting on computer.Data processing has three distinct stages: Input ProcessingOutput

(Information) (Computer) (Data & Instructions)

Reasons for Computerized Accounting:

Processing of Numeric Data: Computerisation can process numeric data more easily than the data processed manually.

Use of Algorithm: Computers can take up a job if the same task is algorithm.

Speedy Processing: Introduction of Computers in accounting has assured speedy processing of voluminous data and that too without errors of calculations.

Existence of Standards: It is relatively much easier to maintain standards and controls in computerised accounting.

Question 7: How computerised accounting different from Manual Accounting?

Answer: Computerised accounting system requires the data inputs be arranged in specific formats. Transactions with missing dates, account numbers or other critical information are not accepted by the system.Some of the processes in the computerised system are automated. Some of the time consuming processes are eliminated in the computerised system.Computerised accounting system is pre programmed and some defaults may also be set to eliminate human errors.On the computerised system, any transactions or data is automatically updated and reports are readily available at any time.

Question 8: What is Inventory Control System? Explain its objectives.

Answer: Inventory Control is a system, which ensures that right quality of inventory is available in the right quantity at the right time and right place with right amount of investment.

It involves inventory planning and decision making with regard to the quality and time of purchase, fixation of stock levels, maintenance of stores records and continues stock taking.

Objectives of Inventory Control System:

Ready Availability of Stock: A continuous availability of all types of material in the factory is required so that production may not be held up for want of any material.

Minimum Investment: Overstocking is to be avoided as it has lot of cost attached to it. More stock means more investment which could otherwise be made in better business propositions.

Minimum Wastage: Inventory control aims at minimising wastage at the time of storing and handing stocks through scientific techniques.

Reasonable Price: The price should be reasonably low; however, quality is not to be scarified at the cost of low price.

Information about availability of material: Information about different items of stock should be readily available to the management so that proper planning can be made for future.

Optimum use of Men, Machines and Materials: Inventory control helps in uniform and proper utilization of resources available with the enterprises.

Maintaining Different Levels of Stock: With the help of Inventory Control System, different levels of material, viz. minimum level, maximum level, danger level and reordering levels are maintained.

Question 9: What is Sales Order Processing?

Answer: When goods are sold to customers on credit they become debtor of the business. The debtors are allowed fixed credit period within which they are supposed to make the payment. The occurrence of bad debts and low rate of realisation from debtors are the results of poor monitoring and control system.Features:

Setting Credit Limits and Credit Periods: Credit limit is the amount, which can easily be granted to a party. Credit limit is set to ensure safe recovery of debts.

Enforcing Credit Control: Tally will refuse to accept the voucher in case the outstanding balance exceeds the limit.

Report on Outstanding: Tally provides complete bills which are overdue and with details of amount receivable from different parties.

Age wise Analysis of Outstanding: Tally prepares Age wise analysis reports to find out the range of period for which bills have been outstanding.

Calculation of Interest: The method of calculating interest is specified at the time a ledger is created.

Reminder Letters: The amounts of bills outstanding along with interest hereon are displayed in reminder letters.

Question 10: What is Payroll Accounting System? Explain need of Payroll Department.

Answer: Payroll Accounting is concerned with the maintenance of records for the amounts due to the employees like salaries, wages, allowances, contributions to provident fund, E.S.I etc. and the deductions like tax, recovery of advance etc. to be made from the employees earnings.Need of Payroll Department:

to maintain a record of the job classification and wages rate for each worker

to verify the time of each worker as shown on the time cards

to calculate the wages due to each other

to prepare the pay roll or wages sheet for each department

to maintain a permanent pay roll records for each employee

to distribute wages and salaries

Paper: P.G.D-04Sub: Computer Networks & Data Communications

Question 1: Write a short note on ARPAnet.

Answer: ARPAnet: A wide area network (WAN), created in 1969 with funding from the Advanced Research Projects Agency (ARPA). ARPAnet served as the test bed for the development of TCP/IP (the protocols that makes the Internet possible). A major goal of the ARPAnet project was to increase the militarys command and control capability enabling communication across a variety of physically dissimilar media, including satellites.Most ARPAnet users preferred to use the network for communication, such as electronic mail and discussion groups. Initially, the ARPAnet was available only to government research institutes and to universities holding Department of Defence (DoD) research contracts.The backbone of the ARPAnet consisted of packet switching computers called IMPs (Interface Message Processors) connected by for the time superfast 56 Kbit/s lines.

Question 2: What are LAN properties and its components?

Answer: LAN (Local Area Network):A LAN is a high speed data network that covers a relatively small geographical area. It typically connects workstations, personal computers, printers, servers, and other devices. LAN offers shared access to devices and applications, file exchange between connected users and communication between users via electronic mail and other applications.

Properties of LAN:

Multiple systems attached to shared computer

High total bandwidth

Low delay

Low error rate

Limited geography (1-2km)

Limited number of stations

Peer relationship between stations

Confined to private property

Components of LAN:

Hardware

Workstations

Server

Network operating software (NOS)

Wiring

Topology

Workstation: In networking, workstation refers to any computer to a local area network. It could be a workstation or a personal computer.

LAN Server:

A local area network (LAN) server is a program that serves the resources (files, storage, application programs, printers and other devices for a number of attached workstations.

Network Operating Software: An operating system is the program that acts as the intermediary between the user and the computer hardware. The most fundamental of all system programs is the operating system, which controls all the computer resources.

Wireless LAN:Wireless LANs are becoming more popular, but are a costly alternative to wired versions. The technology uses radio frequencies and the server can be mobile as data travels through the air. Wireless LANs are very easy to install. There is no requirement for wiring every workstation and every room. This ease of installation makes wireless LANs inherently flexible.

Question 3: Differentiate between FDM and TDM.

Answer: FDM (Frequency Division Multiplexing): When the available frequency range is divided among many signals, the process is known as frequency division multiplexing. It is used in analog communications. The modulated carrier frequencies are combined for transmission over a single line by a multiplexer (MUX). It preserves compatibility with monorecievers and requires only a slight increase in BW.FDM techniques are used to transmit these two independent signals on a single channel.

TDM (Time Division Multiplexing):In TDM, instead of dividing the available bandwidth of the channel among many signals as in FDM, the entire bandwidth is used for each signal.The use of TDM offers even greater system improvements.TDM is a protocol insensitive and is capable of combining various protocols and different types of signals such as voice and data.There is no need for guard bands.

Question 4: Which features differentiate a MAN from LAN and a WAN?

Answer: There are three important features which differentiate MAN from LAN and WAN:

1. The network size falls intermediate between LANs and WANs. A MANtypically covers an area of between 5 and 50 km range. Many MANs cover an area the size of a city, although in some cases MANs may be as small as a group of buildings

2. A MAN (like a WAN) is not generally owned by a single organisation. The MAN, its communications links and equipment are generally owned by either a consortium of users or by a network service provider who sells the service to the users.

3. A MAN often acts as a high speed network to allow sharing of regional resources. It also frequently used to provide a shared connection to other networks using a link to a WAN.

Question 5: What are the various variations of DSL technology in modems?

Answer: The various variations of DSL technology in modems are:

Asymmetric DSL (ADSL): It is called asymmetric because the download speed is more than upload speed. ADSL works this way because most Internet users download much more information than they send (upload).

High bit rate DSL (HDSL): Provides transfer rates of about 1.5Mbps. HDSL receives and sends data at the same speed, but it requires two lines that are separate from the normal phone line.

Symmetric DSL (SDSL): Like HDSL, this receives and sends data at the same speed. While SDSL also requires a separate line from the phone, it uses only a single line instead of two as used by HDSL.

Very high bit rate DSL (VDSL): An extremely fast connection, VDSL is asymmetric, but only works over a short distance using standard copper phone wiring.

Question 6: What are the advantages of optical fibre systems?

Answer: The advantages of optical fibre systems are:

very high capacity

long repeater spacing

small cable dimensions

low weight

small bending radius

no crosstalk

immunity to electromagnetic interference

Question 7: What is PPP? Explain the features of PPP?

Answer: PPP is Point to Point Protocol which handles error detections, supports multiple protocols, allows IP address to be negotiated at connection time, permits authentication.PPP provides three features:

1. A framing method that unambiguously delineates the end of one frame and the start of the next one. The frame format also handles error detection.

2. A link control protocol for bringing lines up, testing them, negotiating options and bringing them down again gracefully when they are no longer needed.

3. A way to negotiate network layer options that is independent of the network layer protocol to be used.

Question 8: Write short note on the network layer of OSI reference model.

(Application)Answer: Network Layer is at position third of the OSI Model. Various layers of OSI reference model:

(Physical) (Data Link) (Network) (Transport) (Session) (Presentation)

The Network layer is responsible for finding path to destination and forwarding packets towards destination depending upon the path information. Apart from finding route and forwarding of packets this layer is also concerned with issues of network addresses, internetworking error handling, congestion control and packet sequencing.

The Network layer is concerned with controlling the operation of the subnet. To control operations it must be aware of topology of the communication subnet. It is also up the network layer to deal with the packets of different formats.

The Network layer defines the network address, which differs from MAC address. Some network layer implementations, such as the Internet Protocol (IP), define network address in a way that route selection can be determined systematically by comparing the source network with the destination network address and applying the subnet mask.

The Network layer is concerned with the path through the network. It is responsible for routing, switching and controlling the flow of information between hosts. The network layer converts the segments into smaller datagram than the network can handle: network hardware source and destination addresses are also added. The Network layer does not guarantee that the datagram will reach its destination.

Question 9: What are the advantages of OSPF?

Answer: Advantages of OSPF are:

changes in an OSPF network are propagated quickly

OSPF is hierarchical, using area 0 as the top as the hierarchy

OSPF is Link State Algorithm

OSPF supports Variable Length Subnet Masks (VLSM)

OSPF uses multicasting within areas.

OSPF is an open standard, not related to any particular vendor

After initialisation, OSPF only sends updates on routing table sections which have changed, it does not send the entire routing table

Question 10: Identify the basic components of a communication system.

Answer: The basic purpose of any communication system is the exchange of data between two parties.Basic components of a communication system:

Source: This device generates the data to be transmitted. For example, telephones and personal computers.

Transmitter: A transmitter transforms and encodes the information so as to produce electromagnetic signals that can be transmitted across some sort of transmission system. For example, a modem takes a digital bit stream from a pc and transforms into an analog signal and sends it to telephone network.

Transmission system: This can be a single transmission line or a complex network which includes transmitting device.

Receiver: It accepts the signal from transmission system and converts it into a form that can be managed by the destination device. For example, modem.

Paper: P.G.D-05Question 1: What are the important points to remember about functions?

Answer: Points to be remember about functions are:

Any C program contains at least one function.

If a program contains only one function, it must be main () function.

In a C program if there is more than one function present then one of them must be main ().

There is no limit to the number of functions that a program may contain.

Any function can be called from any other function.

A function can be called any number of times.

A function can also called itself. Such a process is called recursion.

The main () function controls how the other functions are to be called.

A function can be called from other function, but cannot be defined in another function.

The order in which the functions are defined in a program and the order in which they get called need not be the same.

Question 2: What is an operator? Describe several different types of operators included in C.

Answer: An operator in a language acts on one or more operands to yield a value. An operand is an entity on which an operator acts.

Unary operators: The unary operator requires only one operand. -, +, --, ++ are unary operators.Binary operators: These operators require two operands. The arithmetic operators +, -, /, % and * are binary operators

Ternary operators: The one and only one ternary operator in C, also called ?: operator or conditional operators, requires three operands as Test operand? operand-2: operand-3There is other classification of operators also: 1. Arithmetic operators: The symbols used for various arithmetic operations (like +, - etc.) are called arithmetic operators.

Operator

Operation

Example

+

Addition

X+100

-

Subtraction

200-y

*

Multiplication

x*y

/

Division

x/y

%

Modulus

x%y

2. Relational operators: These operators are used to compare various expressions. They check the relation between the expressions.

Operator

Operation

Example

10

=MAX

==

Equal to

M==1000

!=

Not equal to

Seats !=0

3. Logical/ Boolean operators: The logical operators are symbols that are used to combine or negate expressions containing relational operators.

Operator

Operation

Example

&&

And

x>1 && x60 || job= N

!

Not

! (x>100)

4. Assignment operators: These operators assign a value to the variable on the left hand side of the assignment statement. The operator = is called assignment operator.

Operator

Operation

Example

Result

=

Assignment

x = 10

X=10

+=

Addition update

Sum += x

Sum=sum+x

-=

Subtraction

Tot -= 1

Tot=tot-1

*=

Multiplication

x *=y

x=x*y

/=

Division

x /= y

x=x/y

%=

Modulo

x %= y

x=x%y

5. Bitwise operators:

Operator

Operation

Example

2

&

AND of bits

x&y

|

Inclusive OR of bits

x|y

^

Exclusive OR of bits

x^y

Question 3: Discuss the salient features of C language.

Answer: The salient features of the C language are:

1. It is a block structured language with fundamental flow-construction statements.

2. It has close interaction with the computers inner working.

3. Simple, contained, versatile, more expressive general purpose language.

4. Excellent and efficient language for a variety of applications.

5. It has high degree of language mobility. Functions can be written a with lines of code thus making program development easier.

6. It is fast and efficient.

7. C is function oriented. Rich library of ready-programmed functions available.

8. Rich set of operators are available.

9. Dynamic storage allocation possible.

10. C permits data conversion, mixed mode operations.

Question 4: What is the purpose of the for statement? How does it differ from the while statement and the do-while statement?

Answer: The purpose of the for loop is to execute a statement or a group of statements fixed number of time. The syntax of for statement is:

for (expression1; expression2;expression3)

{

statement-one;

statement-two;

statement-so-on;

}

statements-when-expression2-become-false;

In this statement, expression1 is used to initialise the variable the controls the loop e.g. counter=1. The expression2 is the test expression; the loop continues till the expression2 is true e.g. counter