The Local Area Network (LAN) is by far the most common type of data network. As the name suggests, a LAN serves a local area (typically the area of a floor of a building, but in some cases spanning a distance of several kilometers). Typical installations are in industrial plants, office buildings, college or university campuses, or similar locations. 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 and MANs using a "router".
In summary, a LAN is a communications network which is:
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.
Networking Equipment at the centre of a LAN
The photograph shows some of the networking equipment at the centre of the LAN used by the Communications Group in the School of Engineering. Unshielded Twisted Pair cabling (UTP) enters the rack from the five research laboratories and is terminated on the patch panel (housed in the bottom box). Each outlet is connected via a coloured patch lead to either a 10 or 100 Mbps Ethernet Switch (blue, above the patch panels).
Access to the remainder of the campus network is controlled via a TCP/IP Internet Router (blue, with cables connected at the rear). A second switch/router may be used to connect other equipment (white) forming separate experimental test LANs. The two smaller boxes on top are Ethernet Hubs for connecting groups of workstations, similar hubs also provide connection for the fibre optic links to other parts of the University.