Introduction
The connection of a device into a LAN is made through a node. Anode is any point where a device is connected and each node is allocated a unique address number. Every message sent on the LAN must be prefixed with the unique address of the destination node. LANs operate at relatively high speed (i.e. 2 - 100 Mbps range and upwards) with a shared transmission medium over a fairly small local area.
In a LAN, the software that controls the transfer of messages among the devices on the network must deal with the problems of sharing the common resources of the network without conflict or corruption of data. Since many users can access the network at the same time, some rules must be established on which devices can access the network, when and under what conditions. These rules are covered under the general subject of access control. The rules that apply depend on the structure and type of the network, e.g. a star, ring or bus topology and a token passing or CSMA/CD network type.