A LAN (Local Area Network) is by far the most common type of data network.

A LAN would normally be found in a small office complex, industrial sites or a location with several buildings which could span quite large distances but still be called a Local Area Network. In these locations, it is feasible for the owning Organisation to install high quality, high-speed communication links interconnecting nodes. Typical data transmission speeds are one to 100 megabits per second.

A wide variety of LANs have been built and installed, but a few types have more recently become dominant. The most widely used LAN system is the Ethernet system developed by the Xerox Corporation.

Intermediate nodes (i.e. repeaters, bridges and switches) allow LANs to be connected together to form larger LANs. A LAN may also be connected to another LAN or to WANs (Wider Area Network) or to MANs (Metropolitan Area Network) using a "router".

A LAN communications network could be described as being:

• Local (i.e. one building or group of buildings on the same site);
• Controlled by one administrative authority;
• Assumes other users of the LAN are trusted;
• Usually high speed and is always shared;

LANs allow users to share resources on computers within an organisation, and may be used to provide a (shared) access to remote organisations through a router connected to a Metropolitan Area Network (MAN) or a Wide Area Network (WAN).

Metropolitan Area Network (MAN)

A MAN network would fall between LANs and WANs. A MAN typically covers an area of between 5 and 50 km diameter. Many MANs cover an area the size of a city, although in some cases MANs may be as small as a group of buildings or as large as the London City area.

A MAN (like a WAN) is not generally owned by a single organisation. The MAN, its communications links and equipment are generally owned by either a consortium of users or by a single network provider who sells the service to the users. This level of service provided to each user must therefore be negotiated with the MAN operator, and some performance guarantees are normally specified.

A MAN often acts as a high speed network to allow sharing of regional resources (similar to a large LAN). It is also frequently used to provide a shared connection to other networks using a link to a WAN.

Wide Area Network (WAN)

The WAN is a communications network that makes use of existing technology to connect local computer networks into a larger working network that may cover both national and international locations. This is in contrast to both the local area network and the metropolitan area network, which provides communication within a restricted geographic area. Here is how the wide area network functions, and why it is so important to communications today.