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LESSON :1

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ObjectivesAt the end of this session, you will be able to:

List the advantages of using computer networks

Classify computer networksDifferentiate between LAN ,MAN and WAN

Differentiate between peer to peer networks ,server based

networks and combination networks

Explaining the functioning of the standard topologyUnderstanding the functioning of a hub

Explaining some other topologies used in computer networks

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COMPUTERNETWORKS

Is a group of computers connected by using various media

Is capable of sharing, managing and providing the following

resources:

Printers

Scanners

Hard disks

Floppy disks

CD-ROMs

PlottersOther devices

Keeps information reliable and up to-date

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A simple network

Computers

Printer

Cable

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Computer Network

(contd)

Providescentralizeddatastorage

Providesfasterdatasharing

Isused for efficient communication

between workgroups by using:

Electronic mail

Online conferencing

GroupWare

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Scheduling a meeting with Microsoft Schedule+

Staff meeting

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TYPES OF NETWORKSOn the basis of the area covered, networks

are classified into:

Local Area Network (LAN)

Metropolitan Area Network (MAN)

Wide Area Network (WAN)

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Common network elements

ClientsServer

Data

Printer(shared peripherals)

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Local Area Network

Is confined to a single location

Uses cables as its connecting media

Has the maximum distance betweennetworks limited by:

The strength of the signal

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Metropolitan Area Network

Covers a much larger area compared

to LAN

Uses the LAN technology Carries information in the form of

computer signals

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Wide Area Network

Covers a larger area compared to LAN

Carries information in the form of

signals from one computer to another

Is spread over wide areas such as:

Cities

States

Countries Establishes communication via:

Telephone lines

Satellites

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Advantages of

LAN over WAN

LAN designers can set up their own network

that is technically reliable

Whereas WAN designers are forced to use

existing public telephone network that

is technically unreliable

LAN cables are more reliable since the error

rates are lesser than in WAN Error detection and correction are done at lower

levels in LANs as compared to WANs

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Roles of Computer in a Network

Clients

Which use network resources but do notshare them

Peers

Which use and share network resourcesServers

Which provide network resources

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Roles of Computers in a Network

(contd.)On the basis of the roles, networks are

divided into three categories:

Peer-to-Peer networks

Server-based networks

Combination networks

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Typical peer-to-peer and server-based networks

Peer-to-peer

Server-based

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Peer to Peer networks

Does not have a central control over the

network

Computers are clients as well as servers

Does not have any dedicated server

Is organized into workgroups that have

limited security control

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Peer-to-peer network computers act as both clients and

servers

Client/Server

Peer-to-peer

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Peer to Peer Networks (contd)Offers the following advantages: No extra investment on server

hardware and software Easy setup

No network administrator required

Users can controls sharing ofresources

Less cost

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Peer-to-Peer Networks (contd.)Have the following disadvantages:

Weak and intrusive security

Need to administer the computers

Lack of centralized management

Additional burden on the computersbecause of resource sharing

Non-handling of multiple network

connections

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Server-based Networks

Are organized into domains in a Windows 2000

environment that provide:

Security

Administration

Provide services to various clients

Ensure security of files and directories

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Server-based network

Server

Clients

Server-based

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Server-based Network (contd)Provide servers called domain controllers

that are categorized into:

Domain Controllers

Member Servers

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Server-based Networks (contd.)Offer the following advantages:

Strong central security

Centralized file storage that: Provides easy backup of critical data

Allows users to work with the same set of data

Reduced overall costs Easy management of multiple users

Users are freed from managing resources

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Server-based Networks (contd.)

Have the following disadvantages:

Expensive dedicated server

Expensive network operating system

software and

Need for a dedicated network

administrator

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Specialized servers

Directoryservicesserver

Mailserver

Applicationserver

File andprint server

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Servers

Are dedicated to perform specific tasks

May perform all the tasks

or have separate servers for each task

Are classified into:

File servers that allow users to share files

Print servers that allow users to print on a commonnetwork printer

Application servaers that allow clients to accessexpensive software applications

Message servers that provide message services

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Combination Networks

Combine server-based and peer-to-peer

networking features

Can be implemented by using two types of

operating systems on the same network

Require extensive planning and training of

the users to implement the network and

security issues

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Combination networks have dedicated servers and computers

WindowsNT Server

Windows

forWorkgroups

Windows 95

Windows NT

Workstation

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Network Topology Refers to the arrangement of computers, cables

and other components on a network

Greatly affects the functionality of a network

with respect to:

Types of equipment

Functionality of equipment

Expansion of network Management of network

Determines the:

Kind of cabling required

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Network Topology (contd.)Can be implemented by taking into

consideration the following factors:

Network budget

Network size

Security level

Physical layout of the network

Type of business

Amount of network traffic

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Standard Topologies

Areclassifiedinto:

Bus

Star

Ring

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Bus Topology

Is also known as linear bus topology

Has several computers attached to a common cablecalled the trunk line

Sends data to all the computers on the network

Enabling the computer with the specified address inthe signal to accept the data

Allows only one computer at a time to send messages

Is a passive topology

Brings down the network if one computer fails

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Bus topology network

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Bus Topology (contd.) Can be affected by

Number of computers

Hardware capabilities of computers

Types of cable

Number of times data is transmitted

Distance between computers on the network

Requires terminators to stop the signal from

ringing

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Data is sent to all computers, but only the destination computer

accepts

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02608c133456

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Bus Topology (contd.)

Offers the following advantages:

Is a simple topology

Is reliable for small networks

Is easy to use

Requires least amount of cable to connect

computers

Can be easily extended

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terminators absorb free signals

Terminator

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An unplugged cable is not terminated and will take down the

network

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Bus Topology (contd.)

Has the following disadvantages:

Performance is adversely affected by heavy

network traffic

Electric signals weaken when several

extensions are attached

Troubleshooting is difficult

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Star Topology Connects computers by cables to a centralized

device called a hub

Sends signals from the sending computer to the

receiving computer through the hub

Requires more cable since each computer is

connected to the central point

May have a disabled network if its central

controller fails

Can be expanded by attaching another star hub

A hub is the central point in a star topology

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Simple star network

Hub

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Star Topology

Offers the following advantages:

Is easy to modify

New computers can be added easily

Network problems are easy to diagnose

Failure of a single computer does not bring

down the entire network

Several cable types can be used with the hub

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Star Topology (contd.)

Has the following disadvantages:

If the central hub fails, the entire network fails

Cabling costs are more

Ri T l

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Ring Topology Connects computers to a single circle of cable

Does not have any terminal ends Causes signals to travel around the loop in

one direction

Affects the entire network if one computerfails to work

Is an active topology

Allows every computer to act as a repeaterthat Boosts the signal

Passes it on to the next computer

Is used in high performance networks

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Simple ring network showing logical ring

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Ring Topology (contd.)

Offers the following advantages: Network efficiency can be as high

Equal access is given to all computers

Suffers from the following disadvantages: Failure of one computer on the ring can affect

the entire network

Troubleshooting is difficult

Adding or removing computers disrupts the

network

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Token

Is a short message passed around the ring Is captured by the computer that has to

transmit the data

Contains : Address of the receiving computer

Data that is to be sent

Is received by the destination computerwhich then sends a receipt to the originator

Is again generated by the originator and sent

over the ring

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A computer grabs the token and passes it around the ring

40080865402

Data

Data

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Hub

Is a device that centralizes network trafficthrough a single connection point

Is classified into:

Active hub: which regenerates and transmits the signal

is also called as multiport repeater

requires electrical power to run

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Passive hub that:

acts as a connection point

does not amplify or regenerate signals

does not require electrical signals

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A hub is the central point in a star topology

Hub

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Other Topologies

Are:

Star Bus Star Ring

Physical Mesh

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Star Bus Topology

Is a combination of the bus and star

topologies

Has several star topology networks linked

with linear trunks

Does not adversely affect the network ifone computer fails

Causes the network to be disabled when

the central hub fails

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Star bus network

Hub Hub Hub

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Star Ring Topology

Is a combination of the ring and

star topologies.

Has hubs that are connected in

a star pattern to the main hub

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Star ring network

Main hub

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Physical Mesh Topology

Has a link between each device on the network

Gets unmanageable beyond a very small number ofdevices

Has each of its computers linked to most of the other

computers reducing the redundant links