CLASSIFICATION OF COMPUTER NETWORKS :-
There are three types of a network.
1. Local Area Network (LAN)
2 . Wide area Network (WAN)
3. Metropolitan area Network (MAN)
A local area network enables you to connect a group of personal computers within a single building or small geographical area while a wide area Network is a network of computers dispersed geographically.
The metropolitan area Network lies between LAN and WAN. It is a network which covers entire city.
Let us discuss these three in more detail.
1. Local Area Network (LAN) :-
When two or more computers are connected in a small area i. e. network is known as local area network.
It is made for an organisation and most of the times it is within a single building.
The data rate in LAN is of order of Mbps i. e. Mega bits per second. A LAN consists of
* Computers
* Graphic stations
* User terminal stations or workstations
* Cables of transmission media
* Peripherals like printer, scanner etc.
All the LAN components are connected through cables or some transmission media.
A LAN may use one of the various to the topologies like star topology, ring topology, bus topology (Dual bus or in the repeater) etc.
A LAN has following characteristics.
It covers an area of less than 5then kilometer.
It provides high speed data communication.
The physical interconnecting medium is privately owned.
The physical inter connecting medium is usually shared by all the stations or nodes connected to LAN.
They have low error rates.
They use simple data communication Protocols
It contain both Hardware and software interface for LAN.
File server, printer server and modem server are three major categories of services use in LAN.
To operate LAN System LAN operating system is required. It has two aspects
* service software
* workstation software
2. Wide Area Network (WAN) :-
A wide area Network is connection of two or more computers which are geographically dispersed.
It wide longer distance communications than LAN.
It used public networks like telephone network or microwave relays for communication facilities.
A cost involved with such networks so highs mostly it is used by government agencies.
WANs in contrast to LAN need involvement of another authority like telecom department.
They use radio waves, microwaves or communication satellites for data transmission.
The hardware components required for WAN include Bridges, routers gateways and X. 25 standard interface.
Bridge is a hardware device which connects two or more local area networks to form a wide area Network.
Generally the LANs connected by it same network Protocol but they can be used with two LAN 's having different wiring or Network Protocols.
The bridge operates at link layer of OSI reference model.
It manages the flow of traffic between two LAN' s by reading the address of every data packet received by it.
The amount of processing required at bridge is minimal because all the devices use the same Protocol.
If the distance between two LAN to be connected is large than two identical bridges at either ends of communication links are employed as shown below in diagram
LAN 1---------------ROUTER------------LAN2
Router is a special type of hardware device which connects two or more dissimilar LAN's to from a WAN.
It is an intelligent connecting device which can send packets to the correct LAN segment for their delivery to the destination.
They operate at network layer of OSI reference model.
The LAN's connected can use similar or different network Protocols.
They computer best routes for data message packets on the basis of information provided by the devices participating in routing Protocol.
Various types of routes are central router, local router, remote router, peripheral router, internal router, external router etc.
Gateway are used to connect two dissimilar LAN's.
It is a shared connection between a LAN and a larger system such as main frame computer or a large packet switching network.
The communication Protocols of all of them are different.
They are slower than a bridge or router.
It has its own processor in it and is a combination of hardware and software both. If contains memory which is used to perform Protocol conversations
Router is another networking device which combines the features of a bridge and router.
It can router one or more specific Protocol it can be used to connect two more similar or dissimilar LAN's to form a wide area Network.
It does not implements a network rather simply interfaces a network.
Two types WAN's are public network and private network. Mostly the topologies used are multi drop topology.
It is a complete network with several layers of Protocols.
* The characteristics of WAN are :
It inter connects computers at different sites.
It can connect two or more LAN's too.
It operates nationwide or world wide.
The transmission media is leased lines or public systems such as telephone lines, micro wave or satellites.
There may or may not be a direct physical connection between various components.
Links are slow as compared to LAN's 1200 kbps to 1.544 maps.
Distance of computers is from several miles to several hundred miles.
Links are error - prone relative to LAN's.
3. Metropolitan area Network (MAN) :-
It resides between LAN and WAN.
It interconnections computer within a city.
It used dual queue dual bus Protocol.
The implementation for MAN provides transfer rates from 34 Mbps to 150 mbps which is not very slow as Compared to LAN. It is designed with two unidirectional bus.
The dual queue dual bus (DQDB) Protocol has two topologies as open bus architecture or closed bus architecture and both are used with MAN.
They use broad band cables as transmission media.
They also use fibre optical cable as transmission media.
A metropolitan area Network (MAN) Connects multiple LANs within a metropolitan area.
This connection provides even more resources for the users on the included LANs.
By interconnecting smaller network within a large geographical area, information is easily disseminated throughout the network.
Local libraries and government agencies often use a MAN to connect to citizens and private industries. Campus network connected through a metropolitan network.
The Metropolitan Area Network (MAN) is the often ignored sibling to LANs and WANs.
A MAN is often seen as an extension of a LAN.
MANs are meant to bridge the geographical differences between LANs and WANs.
LAN and WANs are less than adequate to their needs.
LAN are too small or specialised for some applications while Telnet, timnet or other WANs are overfilled for a modest community of users within at 50km diameter.
This were rise to MAN.
MANs were originally oriented towards data, but now often carry voice and video - traffic as well.
They support two - way communication over a shared medium such as an optical fibre cable and many offer point - to-point high speed circuits or packet switched communication.
They do not however have the capability of a switched exchange network such as the present telephone system or the future broadband Integrated semies digital network which will offer world wide service.
Example of A MAN one of a MAN is the MIND Network located in pasco country, florida. It connects all of pasco's media centres to a centralized mainframe at the district office by using dedicated phone lines, coaxial cabling, and wireless communication provides.
*Characteristics of a MAN :-
In a group of connected computers and associated peripherals that can share files and other resources in large campus or organization spread over a city size area.
MAN is slower than a LAN but faster than a WAN
Expensive Equipment
Moderate Error Rates.
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