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LAN and WAN

Local Area Network (LAN)

Smallnetwork,short distance A room, a floor, a building

Limited byno. ofcomputers anddistancecovered

Usually one kind oftechnology throughout the LAN

Serve a department within an organization Examples:

Networkinside the Student Computer Room

Networkinside University

Networkinsideyour home

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Wide Area Network (WAN) A network that useslong-rangetelecommunicationlinks

to connect 2 or more LANs/computers housedindifferentplacesfar apart.

Towns,states,countries Examples:

Network ofour Campus

Internet

WAN

Student

Computer

Centre

Your home

USA

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Example WAN technologies:

ISDN Integrated ServiceDigital Network Basic rate: 192 Kbps Primary rate: 1.544Mbps

T-Carriers basicallydigitalphonelines T1: 1.544Mbps T3: 28vT1

Frame relay Each link offers 1.544Mbps or even higher

ATM Asynchronous Transfer Mode Support B-ISDN: 155Mbps or 622Mbps or higher

SONET Synchronous Optical Network Basic rate OC1: 51.84Mbps

Support OC12 andup to OC192 (9953.28Mbps) or

even higher in thefuture

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Example ofWAN: Broadband Cable Network

Cable TV services have beenextensivelydevelopedinmost

moderncities

Cable TV companies try to makeuse oftheir coaxialcable

installed (that aresupposed to carry TV signals) to deliver

broadbanddata services

Manycablenetwork wiring has been replaced with hybrid

fiber-coax (HFC)i.e. use offiber-opticcable to connect tothesubscribers buildings, and then the originalcoaxial

cable to connect to each household

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The connection is shared by a

number of subscribers, hence

may raise performance and

security problems

Cable companyCoaxial

Cable

TV

PC

Cable

Drop

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Cableis anasymmetrical technology Downstream: max 36 Mbps Upstream: max 10 Mbps

May be reduced to 3 10 Mbpsdownstream and 2

Mbpsupstream,depending onno. ofsubscribers

Need a specialcablemodemEthernet

link to PC

Coaxiallink

fromcable TV

socket

Teryon Cable Modem

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5. Introduction to Networking

Peer-to-Peer Networks

Peer-to-peer networkis also calledworkgroup

No h

ierar

chy

am

ong

compu

ters a

llareequ

al No administrator responsiblefor thenetwork

Peer-to-peer

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Clients and Servers Network ClientsClients (WorkstationWorkstation)

Computers that request network resources or services

Network ServersServers Computers that manage andprovidenetwork resources

andservices to clients

Usually havemoreprocessingpower,memory and

harddiskspace thanclients

RunNetwork Operating System that canmanagenot

onlydata, but also users,groups,security, and

applications on thenetwork

Servers often have a morestringent requirement onits

performance andreliability

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Advantages ofclient/server networks Facilitate resourcesharing centrally administrate and

control

Facilitatesystem backup andimprovefault tolerance

Enhancesecurity only administrator can have accessto Server

Support moreusers difficult to achieve with peer-to-

peer networks

Disadvantages ofclient/server networks High cost for Servers

Needexpert to configure thenetwork

Introduce a singlepoint offailure to thesystem

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5. Introduction to Networking

Topology 3 basic types How so manycomputers areconnected together?

Bus Topology Ring Topology

Star Topology

Hub

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Bus Topology Simple andlow-cost

A singlecablecalled a trunk(backbone,segment)

Only onecomputer cansendmessages at a time

Passive topology - computer onlylistenfor,notregeneratedata

Star Topology Each computer has a cableconnected to a singlepoint

Morecabling, hence higher cost

Allsignals transmission through the hub; ifdown,entirenetworkdown

Depending on theintelligence ofhub, two or more

computersmaysendmessage at thesame time

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How to construct a networkwith Bus / Star Topology?

Star Topology

Bus Topology

BNC T-Connector

Coaxial

cable

Network Card

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Ring Topology Everycomputer serves as

a repeater to boost signals

Typical way to senddata:

Tokenpassing

only thecomputer who

gets the tokencansend

data

Disadvantages

Difficult to addcomputers

Moreexpensive

Ifonecomputer fails, wholenetworkfails

TT

T

data

T

data

T

dataT data T data

T dataT Ack

T Ack

T Ack

TAck T