Computer Network is a network in which computers are linked by means of communica bon system. In computer network each computer is capable of communicating with each other computer. Though each computer is not directly connected to every other computer through communication channel.

The first and most obvious reason for networking is that once we link computers and they are capable of communication with each other. another advantage of having a network is that it helps an organization to make better use of hardware and software resource. It also provides an improved communication link between users. Networks vary widely in their size , complexity and geographical spread. One way of classifying networks is based on their geographical spread.

On the basis of geographical spread, networks can be classified in to following groups:

1. LAN Local Area Network.
2. MAN Metropolitan Area Network
3. WAN Wide Area Network.
4. VAN -> Value Added Network.

A LAN simply stated is a handful of PCs connected to each other limited to one geographical site. LAN refers to a network confined to a Local Area like Network used to interconnect computers in a single room or in a building. Local Area Network arouse out of the continous evolution of packet communication networks and computer hardware. LAN came into being to meet the growing demand for high data rate and low cost of communication among these machines.

There are four basic component in a LAN :- station, server, network interface unit and communication channel. LAN's normally transmit data in a digital form using media such as coaxial cables. In LAN PCs or computers are connected together to share information and communication YAM one another in a location. There are two models of LAN peer to peer and master slave.

As the name suggests this refers to a network confined to a metropolition area used to connect branches of outlets of organisation , or to exchange inter organisational information in a city. They have been absorbed by a modem day network.

A WAN is a group of computers that are separated by large distance and linked together. WANs are spread across countries and even countries. This term WAN is used to describe a computer network spanning a regional, national or global area. In such a network, manufacturing centers, distribution centers and regional accounting centers across continents are all connected to national headquarters and therefore to each other. WAN provides a unique environment to facilitate employee communication and to overcome time lags involved in inter-office communication.

A VAN can be defined as a computer communication network that utilizes existing common comer network for transmission while providing added data features with separate equipments. One VAN in use today is TYM Share PDNS and VANs work most effectively by making use of packet switching

Local Area Network are being welcomed by users as well as manufacturers of distributed data processing systems because they eliminate problems at every level of the system and satisfy the need for efficient communication by enabling a collection of an expensive computers to share not only data information but also the expensive peripheral equipments like printers. In fact a good Local Area Network is the heart of an efficient distributed processing system.

Metropolitan Area Networks are used to connect branches or outlets of organisation or to exchange inter-organisational information in a city. They mainly are used for community services, not so popular today. They have been absorbed by modern day networks.

By using Wide Area Networks multinational corp. having a large installation efficient exchange of information. WANs are used only for oriented activities like mail, file transfer etc. WANs also overcome time lags involved in inter office communication.

Value Added Networks are a type of communication networks that utilizes existing common comer networks for transmission, while providing added features with separate equipments. ISDN has proved to be the cheapest way of bringing affordable high speed data communication to the increasing networked world.

1. 4. 4. WAN Card NW 56 CSU / DSU WAN CARD that provides economical connectivity for novell multi protocol router 3.0 version DOS or switched 56.

1. Elite Series :- A family of ISDN modems that provide both ISDN and V.34 transmission capabilities in a single device operates in DOS, WINDOWS, OS/2, MACINTOSH, UNIX and novell environments.
2. ISDN: 2 Multi-backup Unit :- Uses one dial up ISDN line to provide backup for upto six 56/64 KBPS or 128 KBPS circuits.

In the end we can say that with the growth of networks like LAN , MAN, WAN, & VAN sharing of information between users has become a lot easier. This has greatly affected data communication which deals with the electronic transfer of data between computers. The uses and various products of these networks shows the contribution made by networks in the communication world. It is expected to grow more with advent of new technologies in the coming years