Token Ring: 30 Years Old and Still in Service

If you have ever worked on IBM mainframes, AS400s, RS6000s, or any other SNA devices, chances are good that you have worked with Token Ring. And just as the mainframes were supposed to go away with the huge "client/server" push of the 1990s, eventually so would Token Ring networks. But the mainframes never become "extinct" like they were supposed to, and neither did Token Ring networks. The "big iron" mainframes are still present in many large networks, and most of them carry legacy Token Ring networks with them.

Token Ring was conceived by IBM in the early 1970s, and it quickly became IBM's LAN of choice. Soon IBM front-end processors, such as the IBM 3745s, were shipping with Token Ring interfaces. At the time, Token Ring provided a fast LAN medium. Ethernet networks were operating at speeds of 10 Mbps or less on shared-media networks. It was highly debated how much "real" throughput you could get on an Ethernet segment with collisions and a large number of users. As you will see, Token Ring is somewhat deterministic and uses a token-passing technology that allowed it to achieve the speeds that it was advertising, 4 Mbps and 16 Mbps.