On token protocols for high-speed multiple-ring networks

A token ring protocol which restricts the transmission rights to the station possessing the token is not a good candidate for driving a gigabit network. This is due to the fact that the periods while the token is \in transit" are wasted: they must be subtracted from the eeective throughput achievable by the network. As the network's transmission rate becomes higher, the impact of the token transition time becomes more pronounced and the eeective throughput of the network becomes a smaller and smaller fraction of the nominal channel capacity. In this paper, we present a collection of token passing protocols for ring networks which are devoid of this unpleasant property. The protocols are simple and inexpensive, yet they possess a number of advantageous properties as high capacity (similar to metaring and independent of the propagation length of the ring), fairness, and natural accommodation of synchronous and isochronous traac. Our protocols operate on multiple rings. As these rings can be virtual, i.e., obtained by a logical division of a single physical ring, the proposed solutions can be naturally combined with wave division multiplexing techniques.