by Hans Hell

Created on: October 21, 2010

A computer network is a system consisting of two or more computers linked together so that they can exchange data with each other. A small network can be connected with another to form a larger network. The largest network is the Internet, which is composed of many different networks, both large and small.

LAN, WAN, MAN
Networks is called for different things depending on how large area they cover. The most common is called a LAN (Local Area Network) which is a network that typically stays within the same building. However, there is nothing that prevents even a LAN to be spread among several buildings or in a campus for instance. A LAN is often referred to as just local network. Everything from small home networks to fairly large enterprise networks belong to this group.

A LAN consist physically of:
1. Network adapters in all the computers.
2. Cables, often twisted pair type, so-called TP-cables.
3. Hubs
4. Switches (can filter traffic at low levels).
5. Routers and Gateways; for the forwarding of the traffic to other networks.

A network that stretches between several buildings, often far from each other, or between different cities is called a WAN (Wide Area Network). A WAN consists mostly of two or more LAN's connected together and forming the larger WAN. A very good example of a WAN is the Internet. The WAN often uses TDM-based (Time Division Multiplex) high-speed links such as ATM (Asynchronous Transfer Mode).

Many WAN’s are built for a particular organization and are therefore private. Others, built by Internet Service Providers (ISP), provide connections from an organization's LAN to the Internet. WAN are often built of leased lines. At each end of a leased line, you use a router to connect to the LAN in one part of the hub and the other for connecting to the WAN. Leased lines can be very expensive. Instead of using leased lines, you can use the circuit-switched or packet-switched that is less expensive to connect to the WAN.

Somewhere between the LAN and WAN is something that is called MAN (Metropolitan Area Networks). A MAN is larger than a LAN and connects LAN's within a limited area, such as a city, with high capacity. Municipal networks are an example of different kinds of MAN. MAN is a newer concept than the other two and is not used quite as often. It is not wrong to call the MAN for a WAN as the MAN also consists of multiple LAN's, this can bring in some confusion.

SUMMARY
At first sight the different meanings and abbreviations can appear confusing for someone uninitiated, but it's basically to understand the meaning of the abbreviations in order to be enlightened of the function. In chronological order from your computer and out to the Internet the setup is basically something like: Computer -> Network card -> Cable -> Router (this is the LAN) -> ISP -> Internet (reaching the WAN).
In some instances the traffic will also pass a MAN on the way, if you for example are connected to a Municipal network, or from a campus.

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