networking final

8/2/2019 Networking Final

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Computer Networks

A computer networkis a system for communicating

between two or more computers and associated

devices. It is an interconnection of computers for the

purposes of sharing information and resources.

A popular example of a computer network is theinternet, which allows millions of users to share

information

Computer networks can be classified according to their

size: Personal area network (PAN)

Local area network (LAN)

Metropolitan area network (MAN)

Wide area network (WAN)


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Router

An example of a network

Internet

Segment Node

Hub

Hub

Bridge


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Personal Area Network

A PANis a network that is used forcommunicating among computersand computer devices (includingtelephones) in close proximity ofaround a few meters within a room

It can be used for communicatingbetween the devices themselves, orfor connecting to a larger network

such as the internet PANs can be wired or wireless

PANs can be wired with acomputer bus such as a universalserial bus: USB (a serial busstandard for connecting devices toa computer, where many devices

can be connected concurrently) PANs can also be wireless

through the use of bluetooth (aradio standard designed for lowpower consumption forinterconnecting computers anddevices such as telephones,printers or keyboards to thecomputer) orIrDA (infrared dataassociation technolo ies


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A LAN is a network that is used for communicating

among computer devices, usually within an office

building or home

LANs enable the sharing of resources such as files

or hardware devices that may be needed by multipleusers

Is limited in size, typically spanning a few hundred

meters, and no more than a mile

Is fast, with speeds from 10 Mbps to 10 Gbps Requires little wiring, typically a single cable

connecting to each device

Has lower cost compared to MANs or WANs

Local Area Network


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every computer has the potential to communicate with any other

computers of the network

high degree of interconnection between computers easy physical connection of computers in a network

inexpensive medium of data transmission

high data transmission rate

Advantages The reliability of network is high because the failure of one computer inthe network does not effect the functioning for other computers.

Addition of new computer to network is easy.

High rate of data transmission is possible.

Peripheral devices like magnetic disk and printer can be shared by

other computers.

Disadvantages If the communication line fails, the entire network system breaks down.

Major Characteristics of LAN


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Use ofLAN

Followings are the major areas where LAN

is normally used

File transfers and Access

Word and text processing

Electronic message handling

Remote database access

Personal computing

Digital voice transmission and storage


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Wide Area Network The term Wide Area Network (WAN) is used to

describe a computer network spanning a

regional, national or global area. For example,

for a large company the head quarters might be

at Delhi and regional branches at Bombay,Madras, Bangalore and Calcutta. Here regional

centers are connected to head quarters through

WAN. The distance between computers

connected to WAN is larger. Therefore thetransmission medium used are normally

telephone lines, microwaves and satellite links.


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Characteristics of WANF

ollowings are the major characteristics of WAN. Communication Facility: For a big company spanning over different

parts of the country the employees can save long distance phone callsand it overcomes the time lag in overseas communications. Computerconferencing is another use of WAN where users communicate witheach other through their computer system.

Remote Data Entry: Remote data entry is possible in WAN. It meanssitting at any location you can enter data, update data and query otherinformation of any computer attached to the WAN but located in othercities. For example, suppose you are sitting at Madras and want to seesome data of a computer located at Delhi, you can do it through WAN.

Centralised Information: In modern computerised environment youwill find that big organisations go for centralised data storage. Thismeans if the organisation is spread over many cities, they keep theirimportant business data in a single place. As the data are generated atdifferent sites, WAN permits collection of this data from different sitesand save at a single site.


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Examples of WAN

Ethernet: Ethernet developed by XeroxCorporation is a famous example of WAN. This

network uses coaxial cables for data

transmission. Special integrated circuit chips

called controllers are used to connectequipment to the cable.

Aparnet: The Aparnet is another example of

WAN. It was developed at Advanced Research

Projects Agency of U. S. Department. ThisNetwork connects more than 40 universities

and institutions throughout USA and Europe.


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Difference between LAN and

WAN LAN is restricted to limited geographicalarea of few kilometers. But

WAN covers great distance and operate nationwide or evenworldwide.

In LAN, the computer terminals and peripheral devices areconnectedwith wires and coaxial cables. In WAN there is no

physical connection. Communication is done through telephonelines and satellite links.

Cost of data transmission in LAN is less because the transmissionmedium is owned by a single organisation. In case of WAN the costof data transmission is very high because the transmission mediumused are hired, either telephone lines or satellite links.

The speed of data transmission is much higher in LAN than in WAN.The transmission speed in LAN varies from 0.1 to 100 megabits per

second. In case of WAN the speed ranges from 1800 to 9600 bitsper second (bps).

Few data transmission errors occur in LAN compared to WAN. It isbecause in LAN the distance covered is negligible.


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MAN

It is spread across the city from one organization toanother & Connected with cable has a same componentas that of LAN. MAN is a large network of LANs spreadacross various buildings, organizations withingeographical area of a city or metropolitan city. Thegeographical area may vary from 25 km radius to

100 km radius. The computer in various organizationsand departments are interfaced with each other throughtelephone lines or through separate cable connections.

It is spread across the city from one organization toanother & Connected with cable has a same component

as that of LAN. MAN is a large network of LANs spreadacross various buildings, organizations withingeographical area of a city or metropolitan city. Thegeographical area may vary from 25 km radius to 100km radius. the computer in various organizations anddepartments are interfaced with each other through leaf

telephone lines or through separate cable connections.


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Applications of Networks

Introduction to Computer Networks

Resource Sharing

Hardware (computing resources, disks, printers)

Software (application software)Information Sharing

Easy accessibility from anywhere (files, databases)

Search Capability (WWW)

CommunicationEmail

Message broadcast

Remote computing

Distributed processing


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Network Topology

The network topologydefines the way in

which computers,printers, and other devices are connected.A network topologydescribes the layout ofthe wire and devices as

well as the paths usedby data transmissions.

Introduction to Computer Networks


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Star Network In this configuration, multiple computers are connected

to a host computer. That is, the computers in the networkare not linked directly to each other and cancommunicate only via the host computer. The routingfunction is performed by the host computer, whichcentrally controls communication between any two other

computers by establishing a logical path between them. The hub in a broadcast star network can be active or

passive. An active hub generates the electrical signalsand sends it to all the computers connected it. This typeof hub is called multiple repeater.Active hub require

external power supply. A passive hub is a wiring pannel which acts as a

connection point. It does not amplify or regenerates thesignal. Passive hubs do not require electrical powersupply.


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Advantages1. Star topology has minimal line cost because only n-1 lines arerequired for connecting n nodes.

2. Transmission delay between two nodes do not increase byadding new nodes to the network because any two nodes may beconnected via two links only.

3. If any of the local computer fails, the remaining portion of thenetwork is unaffected.

Disadvantage

1. The system crucially depends on the central node. If the hostcomputer fails, the entire network fails.


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Tree TopologyA tree topology is the variation of a star network. As in a star, nodes in a tree arelinked to a central hub that controls thetraffic to the network. However, not everycomputer plugs into the central hub, majority

of them are connected to a secondary hub,which in turn, is connected to the central hubas shown in the fig. The central hub in thetree is an active hub which contains repeater.The repeater amplifies the signal and

increase the distance where a signal cantravel. The secondary hubs may be active orpassive. A passive hub provides a simplephysical connection between the attacheddevices.


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Advantages

1. It allows more devices to be attached to a single hub and cantherefore increase the distance of a signal can travel betweendevices.

2. It allows the network to isolate and priorities communications fromdifferent computers.

Disadvantage1. If the central hub fails, the system breaks down.

2. the cabling cost is more. N1,n2.= comp.

hub

hub hub

hub

n1n2

n1 n2 n3n2

n3n1

n1 n2


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Ring Network Each computer in the network has communicating subordinates, but

within the ring there is no matter computer for controlling other computers. A node receives data from one of its two adjacent nodes.The only decision a node has to take is whether the data is for its ownuse or not. If it is addressed to it, utilizes it. Otherwise, it merelypasses it on to the next nodes.

Advantages

1. The ring network works well where there is no central-sitecomputer system.

2. It is more reliable than a star network because communication isnot dependent on a single host computer, If a link between any twocomputers breaks down, or if one of the computers breaks down,alternate routing is possible.

Disadvantages

1. In a ring network, communication delay is directly proportional tothe number of nodes in the network. Hence addition of new nodes inthe network increase the communication delay.

2. The ring network requires more complicated control software thanstar network.


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Single ring All the devices on the

network share a single cable

Dual ring The dual ring topology

allows data to be sent in bothdirections.


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Completely Connected Network

(Mesh Network) a completely connected network

has a separate physical link for

connecting each node to any

other node. Thus, each computerof such a network has a direct

dedicated link, called a point-to-

point link, with all other

computers in the network. Thecontrol is distributed with each

computer deciding its

communication priorities.


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Advantages

1. This type of network is very reliable, as any link break-downwill affect only communication between the connectedcomputers.

2. Each node of the network need not have individual routing

capability.3. Communication is very fast between any two nodes.

Disadvantage

1. It is the most expensive network from the point of review of linkcost. If there are n nodes in the network, then n*(n1)/2 links arerequired. Thus, the cost of linking the system grows with thesquare of the number of nodes.


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Multi Access Bus Network A single transmission medium is shared by all

nodes that is, all the computers are attached to thesame communication line (channel). When aparticular computer wants to send a message to

another computer, it appends the destinationaddress to the message and checks whether thecommunication line free. As soon as the linebecome free, it broadcasts (places) the messageon the line, each computer check whether it isaddressed to it. The message is picked up by theaddressee computer, which sends anacknowledgement to the source computer and freethe line. This type of network is also known as

multipoint or broadcasting network.


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AdvantagesAdvantages

1. The main advantage of a multi1. The main advantage of a multi--access bus network is the reduction inaccess bus network is the reduction in

physical line.physical line.

2. The failure of a computer in the2. The failure of a computer in the

network does not affect the networknetwork does not affect the network

functioning for other computers.functioning for other computers.

3. Addition of new computers to the3. Addition of new computers to thenetwork is easy.network is easy.

DisadvantageDisadvantage

1. All computers in the network must1. All computers in the network must

have good communication and decisionhave good communication and decision

making capacity.making capacity.2. If the communication line fails, the2. If the communication line fails, the

entire system breaks down.entire system breaks down.

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