A Local Communications Network Based on Interconnected Token-Access Rings: A Tutorial

Local area networks are expected to provide the communications base for interconnecting computer equipment and terminals over the next decade. The primary objective of a local area network (LAN) is to provide high-speed data transfer among a group of nodes consisting of data-processing terminals, controllers, or computers within the confines of a building or campus environment. The network should be easily accessible, extremely reliable, and extendible in both function and physical size. The rapid advances in computing and communications technology over the last two decades have led to several different transmission schemes and media types that could be used in these networks. The star/ring wiring topology with token-access control has emerged as a technology that can meet all of these objectives. The requirements of small networks with just a few nodes, as well as those of very large networks with thousands of nodes, can be achieved through this one architecture. This paper is a tutorial of the fundamental aspects of the architecture, physical components, and operation of a token-ring LAN. Particular emphasis is placed on the fault detection and isolation capabilities that are possible, as well as the aspects that allow for network expansion and growth. The role of the LAN relative to IBM's Systems Network Architecture (SNA) is also discussed.