Lecture-1 Introduction to Computer Networks

8/13/2019 Lecture-1 Introduction to Computer Networks

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16 January 2010 Shatrunjay Rawat, IIIT Hyderabad 1

Introduction to Computer Networks


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Definition

Computer Networks mean a collection of

autonomous computers interconnected by a

single technology

Group of interconnected computers


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Definition

Computers are autonomous if they areindependent entities and are notin a master-

slaveconfiguration

Computers are said to be interconnectedif

they are able to exchange information


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Definition

Computer Networks

User is aware of the presence of multiple

computers

User explicitly connects or disconnects to another

computer

User explicitly assign a job to a certain computer


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Definition

Distributed System: A non centralisedsystem consisting of numerous computers

that can communicate with one another and

appears to the user as single, large,storehouse of hardware, software and data

It is a software system built on top of a

network Example !orld !ide !eb, cloud computing


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Definition

Distributed Systems

Existence of multiple autonomous computers is

transparentto the user

User is unaware of existence of multiple

processors "computers#$%irtual uniprocessor

&perating 'ystem or Application 'oftware

"Middleware# selects the processor to execute thetask


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Use of Computer Networks

(usiness Applications )ome Applications

*obile Users

'ocial Issues


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Business Applications

+esource sharing ata sharing

Intranet applications

-otices, !ork flow management

E$commerce

.ideo$Conferencing

.oice Communication, etc/


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Home Users

Access to remote information 0ersonal communication

$ E$mail, %oice1%ideo chats

E$Commerce

Education

Entertainment

$ .ideo on demand

$ 2. Channels


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Mobile Users

-otebook computers$ (usiness tra%ellers, students

0As 3 'mart 0hones

$ )ealth workers, Courier 'er%ices

*obile phones

$ Internet, '*', **'

!ireless handsets$ 'ecurity agencies, site engineers, utilities


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Computer Network

Network

C!ent

C!ent

C!ent

Ser"er


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Social Issues

*oral issues 0ri%acy issues

Employee$Employer rights

4egal problems

Computer networks and distributed systems

ha%e a major impact on the society at large


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Some More erminolo!ies


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Communication erminolo!y

2ransmission *odes$ 'erial

$ 0arallel

$ 'implex

$ )alf$uplex

$ 5ull$uplex


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ransmission Mode

'erial Communication$ &ne bit at a time

$ Unidirectional1bidirectional

$'impler physical media

$ Cheaper

$ 4onger distance


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ransmission Mode

0arallel Communication$ *ore than one bit simultaneously

$ (i$directional

$(ulkier media

$ Costlier

$ 'hort distance


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ransmission Mode

'implex Communication$ Unidirectional

$ &pen loop

$Unreliable for data communication

Example 2. (roadcast, 5iber


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ransmission Mode

)alf duplex communication$ (i$directional

$ &ne direction at a time

Example Ethernet "IEEE 678/9#


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ransmission Mode

5ull$uplex$ (i$directional

$ (oth directions simultaneously

$Use bi$directional lines or multiple unidirectionallines

Example 2elephone


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ata 'peed$ (aud

$ (0'

Asynchronous 2ransmission 'ynchronous 2ransmission


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Data Speed

(aud$ *easure of speed for analog signaling

$ Electronic state change per second

'ymbol rate

$ +elated to modulation rate in digital circuits

$ -amed after 5rench engineer :ean *ourice Emile

(audot

$ 4ess rele%ant in practice, only used by telecom h1

w designers


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Data Speed

(0'$ (its per second

$ -umber of bits transmitted per second

$ epends on coding techni;ue used

(0'


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Sync"ronisation

Asynchronous Communication$ -ot coordinated in time

$ Independent transmitter and recei%er

$ 0rior agreement on data rate and character length

$ Use of start bit, stop bit, etc/

$ 'impler

$ Cheaper


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Sync"ronisation

'ynchronous Communication$ Coordinated in time

$ (ound by a common "reference# clock

$ -o use of start and stop bits

$ 4ess o%erheads

$ Costlier


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2ype of 'er%ices$ Connection$&riented

$ Connectionless

$ Unreliable

$ +eliable


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ypes of Ser#ices

Connection oriented$ 'imilar to telephone network

$ Connection 'et$up

$ Use it

$ isconnect

$ (oth ends to be ali%e


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ypes of Ser#ices

Connectionless$ 'imilar to postal system

$ -o connection set$up

$ +ecei%er may be off

$ +esources are not dedicated


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ypes of Ser#ices

Unreliable$ Information sent is not acknowledged

$ 'ender is left guessing

$ Used when an unreported data loss is acceptable

$ -ot related to the >;uality? of communication


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ypes of Ser#ices

+eliable$ Information sent is acknowledged

$ 'ender is certain about the deli%ery of the

information

$ Used in typical data centric applications

$ oes not indicate the >;uality? of communication

media


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Home ask


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Self Study ask

Understand your computer

$ Identify all interfaces1ports of your computer

$ 5ind out whether they are serial or parallel ports

$ 5ind out if they are simplex 1 half$duplex 1 full$duplex


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"ank you$s"atrun%ay&rawat'iiit&ac&in
mailto:[email protected]:[email protected]

Lecture-1 Introduction to Computer Networks

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