GATE Computer Networks Book

Computer Networks for

Computer Science & Information Technology By

www.thegateacademy.com

Syllabus

Computer Networks

Syllabus for Computer Networks ISO/OSI stack, LAN technologies (Ethernet, Token ring), Flow and error control techniques, Routing algorithms, Congestion control, TCP/UDP and sockets, IP(v4), Application layer protocols (ICMP, DNS, SMTP, POP, FTP, HTTP); Basic concepts of hubs, switches, gateways, and routers.

Analysis of GATE Papers (Computer Network) Year

Percentage of marks

2013

7.00

2012

9.00

2011

3.00

2010

8.00

2009

3.33

Overall Percentage

6.513 % 2008

6.00

2007

9.33

2006

7.33

2005

6.00

2004

7.33

2003

5.33

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Contents

Computer Networks

CONTENTS Chapters

Page No

#1 Introduction

1 – 32



Computer Network

1



Goals/ Advantages of Networking

1–3



Components of Network

3



Criteria of a Network

3



Classification of a Network

3



Types of Network Connection

4



Network Topology

4–6



Transmission Modes

6–7



Data and Data Communication

7



The Model

7 – 20



Networks Connecting Devices

20 – 24



Assignment 1

25 – 28



Assignment 2

29



Answer Keys

30



Explanations

30 – 32

#2 Physical Layers (Data rate, Digital transmission)

33 – 47



Introduction

33



Transmission Impairment

33 – 34



Digital transmission

34 – 38



Transmission Mode

38 – 39



Multiplexing

39 – 40



Transmission Media

40 – 41



Assignment 1

42 – 44



Assignment 2

44 – 45



Answer Keys

46



Explanations

46 – 47 th

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Contents

Computer Networks

#3

Medium Access Sublayer (LAN Technologies: Ethernet, Token Ring)

48 – 64



Introduction

48



Multiple Access Protocols

48 – 52



Ethernet Cabling

53



The 802.3 MAC sublayer protocol

54



IEEE standard 802.4-Token Bus

54 – 55



IEEE standard 802.5-Token Ring

55 – 58



Assignment 1

59 – 60



Assignment 2

60 – 61



Answer Keys

62



Explanations

62 – 64

#4

The Data Link Layer (Flow and error control techniques)

65 - 99



Data link Layer Design Issues

65 – 68



Error Detection and Error Correction

69 – 78



Flow Control and Error Control

78 – 91



High-level Data Link Control (HDLC) Protocol

91 – 93



Assignment 1

94 – 95



Assignment 2

95 – 96



Answer Keys

97



Explanations

97 – 99

#5

Routing & Congestion Control

100 – 114



Routing

100 – 101



Routing Algorithms:

101 – 107



Assignment 1

108 – 110



Assignment 2

110 – 111



Answer Keys

112



Explanations

112 – 114

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Contents

Computer Networks

#6

TCP/IP, UDP And Sockets, IP(V4)

115 – 145



Over View of TCP/IP

115 – 117



Network Layer

117 – 121



Addressing on Internet

122 – 126



Subnetting

127 – 131



Other Protocol in the Network Layer

131 – 133



Transport Layer

133 – 137



Assignment 1

138 – 139



Assignment 2

140 – 141



Answer Keys

142



Explanations

142 – 145

#7

Application Layer

146 – 157



The Domian Name Service (DNS)

146 – 147



File Transfer Protocol (FTP)

148 – 149



Trivial File Transfer Protocol (TFTP)

149



Simple Mail Transfer Protocol (SMTP)

149 – 150



Uniform Resource Locator (URL)

150



Multipose Internet Mail Extensions (MIME)

150



Post Office Protocol (POP)

151



Hypertext Transfer Protocol (HTTP)

151



Assignment 1

152 – 153



Assignment 2

154



Answer Keys

155



Explanations

155 – 157

#8

Network Security

158 – 175



Symmetric key or Private key algorithms

158 – 160



Asymmetric key Algorithm (or) Public key Algorithm

160 – 161



Digital Signatures

161 – 162



Firewalls

162 – 168 th

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Contents

Computer Networks



Assignment 1

169 – 170



Assignment 2

171 – 172



Answer Keys

173



Explanations

173 – 175

#9

Module Test

176 - 191



Test Questions

176 – 184



Answer Keys

185



Explanations

185 – 191

Reference Books

192

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Chapter 1

Computer Networks

CHAPTER 1 Introduction Computer Network A computer network is created when several computers and terminal device are connected together by data communication system. A network is basically a communication system for computers. Just as the telephone system allows two people to talk, networks allow computers to communicate. Figure 1.1 illustrate a simple computer network where computer A and B can communicate and share resources through computer C.

A

B

C

Fig. 1.1 Computer A and B can access files on C, and can use the printer connected to C.

Goals / Advantages of Networking (1)

Program and file sharing Software resources can also be used more effectively over a network. With stand-alone computers (i.e. not connected to network), the software used on the computer must be present on each computer’s hard disk. It is also difficult and time consuming to install and th

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Chapter 1

Computer Networks

configure the software individually on every computer. With a network one can centrally install and configure the software, which can be accessed at the entire connected computer. (2)

Network Resource sharing Network resources include printers, plotters, Fax modems, scanners, floppy disks, CDROMS and storage devices (i.e. Hard disks) which can be shared by terminals connected to network. For example the sharing of a resource such as a storage device.

(3)

Database sharing A database program is an ideal application for a network. A network feature called record locking lets multiple users simultaneously access a file without corrupting the data. Record locking insures that no two users edit the same record at the same time.

(4)

Economical Expansion of the PC Base Networks provide an economical way to expand the number of computers in an organization.

(5)

Ability to use network software A class of software called Groupware is designed specifically for networks. It lets users interact and coordinate their activities. Note: Not all software will use a network even if one is installed. You should check the software documentation to see what features, if any, the software provides in a network environment.

(6)

Ability to use electronic mail Electronic mail lets users easily communicate with one another Messages are dropped in “mailboxes” for the recipients to read at a convenient time.

(7)

Creation of workgroups Groups are important in networks. They can consist of users who work in a department or who are assigned to special project. With Netware, one can assign users to groups and then give each group access to special directories and resources not accessible by other users. This saves the trouble of assigning access to each individual user.

(8)

Centralized Management Because Netware user’s dedicated servers can be grouped in one location, along with the shared resource attached to them, for easier management. Hardware upgrades, software backups, system maintenance and system protection are much easier to handle when these devices are in one location.

(9)

Security A network provides more secure environment for a company’s important information. Security starts with the login procedure to ensure that a user accesses the network using his or her own account. This account is tailored (i.e. made according to the user requirements) to give the user access only to authorized areas of the server and the network. Login restrictions can force a user a log in at one specific station and only during specific time frame or period.

(10) Access to more than one operating system Netware provides connections for many different operating systems, including DOS, OS/2, UNIX, and Apple Talk. Users of these systems can access files on the Netware server. th

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Chapter 1

Computer Networks

(11) Enhancement of the corporate structure Networks can change the structure of an organization and the way it is managed. Users who work in a specific department and for a specific manager no longer need to be in the same physical area. Their offices can be located in areas where their expertise is most needed. The network ties them to their department managers and systems. This arrangement is useful for special project in which individuals from different departments, such as research, production and marketing, need to work closely with each other.

Components of Network Computer networks have the following fundamental components: 1. 2. 3. 4. 5.

Server Workstations Network Interface Cards Cabling system Shared Resources and Peripherals.

Criteria of a Network A network must able to meet a certain number of criteria. The most important of these are follows (i) Performance: performance can be measured in many ways, including transmit time and response time. The performance of a network depends upon these following factors: (i) Number of users (ii) Types of transmission medium (iii) Capacity of connected hardware (iv) Efficiency of the software (ii) Reliability: In addition to accuracy of delivery. Network reliability is measured by the frequency of failure, the time it takes for a link to recover from a failure. (iii) Security: Network security issues include protecting data from the unauthorized access.

Classification of network It contains two or more computer along with a transmission path to share information and resource of communication system. By the networking we can make interconnection of two or more network device Depending upon the graphical area, we can divide the computer network in 3 parts. (i) LAN (Local Area Network) (ii) MAN (Metropolitan Area Network) (iii) WAN (Wide Area Network) (i) LAN: It spans over a diameter of 2 km, typically data transfer rate for LAN is 10-100 Mbps, it is used by a signal organization. It propagates high transmission over unexpensive media. Example co-axial cable, twisted pair cable. (ii) MAN: It spans over 10 – 100km diameter. Data rate for MAN is 10 Mbps. Some special equipments are required for transmission. (iii) WAN: It spans across the country or nation. Data transfer rate for WAN is 1.5 mbps. It is used by multiple organizations th

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Chapter 1

Computer Networks

Types of Network Connection In a network two or more device are connected together through link. Link is a path for communication that transfer data from one device to another. There are two possible type of connection. (i) Point to point (ii) Multi-point (i)

Point to point: In this case one device is connected to another device. Link

Work station

Work station

Fig 1.2 Point to Point connection (ii)

Multi-point: Here two or more device are connected to each other. In a multipoint connection the capacity of the channel is shared either spatially or temporarily. Work station Work station Main frame

Work station Fig 1.3 Multi-point connection

Network Topology There are two types of topology 1. Physical topology 2. Logical topology 1.

Physical topology: Physical topology represent the physical structure of computer network. It tells how different computers are connected across its communication path. There are six basic topology possible. (i) Mess (ii) Star (iii) Ring (iv) Hybrid (v) Bus (vi) Cellular

(i)

Mess Topology: In mesh topology every device has a dedicated point to point link to every other device. A fully connected mesh network has n(n − 1)/2 physical channel to link n device. To accommodate that many links, every device on the network must have (n-1) input/output ports.

Advantages (i) Eliminate traffic problems (ii) A mesh topology is robust (iii) It is more secure and private (iv) Fault identification and fault isolation is easy th

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