Multiple Logical Token Rings in a Single High­Speed Ring

Describes a new media access control protocol, the multiple-token protocol, for high-speed ring networks. The purpose of this protocol is to increase the throughput of a token-ring under heavy load, and to decrease the access delay under light load. The protocol maintains several logical token-rings in the single physical ring. The number of logical rings can be changed dynamically by the ring stations according to the ring load. 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 multiple simultaneous transmissions of new frames by different stations and decrease the waiting for a token delay. However, the integration of several token rings in a single media is not straightforward since they interfere with the operation of each other. The present protocol is not the first to enable multiple simultaneous transmissions of frames to a ring network. However, unlike previous protocols, that use the buffer insertion concept combined with some fairness mechanism, the new one uses tokens in order to regulate the access to the ring and to ensure fairness. Unlike buffer insertion rings where data-frames may experience a delay of one data-frame at every intermediate station, in the new protocol the delay in the intermediate stations does not depend on the number of such stations. Moreover, this delay can be reduced even to 0, if needed. The new protocol ensures the removal of a data-frame even if both the destination and the source of the frame fail to remove it from the ring