9 - Ethernet/802.3 and Token Ring/802.5

Abstract

This chapter reviews Ethernet/802.3 and Token Ring/802.5. To begin with, Ethernet, IEEE 802.3, and the IBM Token Ring describe different LAN environments. The IBM Token-Ring specifications and the IEEE 802.5 specifications are very similar, differences do exist. In contrast, the specifications for Ethernet and IEEE 802.3 are dramatically different, different to the point where the two can coexist but not inter operate. The commercial implementations of Ethernet and Token Ring are driven by the Digital Equipment Corporation and IBM. Implementing both allows for offsetting the disadvantages of one type of LAN with the advantages of the other. Ethernet and 802.3 specify a LAN operation at speeds of 10 Mbps; key operations in both are the carrier-detection and collision-sensing mechanisms. On the other hand, Token-Ring networks operate at 4 or 16 Mbps; here, a token, is passed from one system to another. The flow of the token is a logical ring; therefore, the token will always end up back at the originating system. With today's technology it is as easy to bridge a Token Ring and Ethernet network together as it is to bridge Ethernet to Ethernet or to bridge Token Ring to Token Ring.