28 - Local Area Networks

Abstract

A local area network is a data communication network that spans a physically limited area (generally less than a mile or two), provides high-bandwidth communications over inexpensive media (generally coaxial cable or twisted pair), provides a switching capability, and is usually owned by the user. There are radical differences between the network topology for a telephone network and that for a local area network. While a telephone network has a hierarchical form, a local area network has a very regular form that is a star, a ring, or a bus. Each topology is best suited to particular media types, has an optimum routing strategy, and has identifiable reliability characteristics. A polling system is a control scheme used for networks such as military, weather, and airline reservation systems. In a token system, a special bit pattern referred to as the “token” circulates around the ring. The token system provides the fairness and distance insensitivity of the polling system and also provides far more efficient utilization of the medium.