Chapter 9 - Token Ring

Abstract

This chapter presents an overview of token ring networks, IEEE 802.5. Unlike Ethernet/802.3 local area networks (LANs) in which nodes contend for media access, token ring LANs use a token passing scheme—that is, media access in token ring LANs is controlled by the possession of a token. The general issues relating to token passing are discussed including a comparison between the random access and the token passing protocols. The IEEE standards include a second token passing protocol called token bus. A token bus network is characterized as a logical ring on a physical bus. Physically, the network resembles a bus topology, but logically, the network is arranged as a ring with respect to passing the token from lobe to lobe. A token ring network is a local area network (LAN) technology based on a token-passing protocol for media access control. Data frames on a token ring network are transmitted from node to node, in either a clockwise or counterclockwise direction, over a point-to-point link. A token ring LAN is implemented either as a logical ring using a physical ring topology, or as a logical ring structure arranged in a physical star configuration. It is also possible to extend the configuration to include a ring consisting of several interconnected hubs.