Wide Area Network (WAN) Definition
This type of network spans a large geographical area, often a country or continent. IT contains a collection of machines intended for running user programs. These machines are called hosts or end systems. The hosts are connected by a communication subnet. The job of the subnet is to carry messages from host to host, just as the telephone system carries words from speaker to listener. By separating the pure communication aspects of the network from the application aspects, the complete network design is greatly simplified.
In most wide area networks, the subnet consists of two distinct components: transmission lines and switching elements. Transmission lines, also called circuits, channels, or trunks move bits between machines.
The switching elements are specialized computers used to connect two or more transmission lines. When data arrive on an incoming line, the switching element must choose and outgoing line to forward them on. Unfortunately, there is no standard terminology used to name these computers. They are variously called packet switching nodes, intermediate systems, and data switching exchanges among other things. The generic term for the switching equipment is a router.
In most WANs, the network contains numerous cables ot telephone lines, each on connecting a pair of routers. If two routers that do not share a cable nevertheless wish to communication, the must do this indirectly, via other routers.
- Local Area Network