Multiple Logical Token-Rings in a Single High-Speed Ring

The present paper describes a MAC protocol for a high-speed ring with multiple tokens. The purpose of this protocol is to increase the throughput and to improve the delay-throughput characteristic of high-speed token-rings. The main concept of the new MAC protocol is to maintain several logical token-rings in the single physical ring. Each logical ring has its own token, and its operation is close to a token-ring with early-token-release and destination removal. Multiple tokens enable several concurrent transmissions of new data-frames by different stations on different logical rings, and decrease the average waiting time to receive a token. However, the integration of several token-rings in a single media is not straightforward, since they interfere with the operation of each other. In the new protocol, the number of logical token-rings can be changed dynamically. The ring stations need not be notified about such changes, since they execute the same algorithm independently of the number of tokens. Moreover, adding or deleting a logical ring is a simple task that can be done by each station in a local manner. The mechanism for this task is also described in this paper. The optimal number of logical rings should change with the ring load: when the load increases, the number of logical rings should be decreased, and vice versa. Since the ring load is a dynamic parameter that may change frequently, the fact that the stations' algorithm is independent of the number of logical rings, and the simplicity of adding and deleting a logical ring, play a key role in achieving high performance at all possible loads.