DOUBLE-TOKEN RING CHANNEL ACCESS PROTOCOL.

The problem of improving token ring networks is studied. We present a double-token channel access protocol in which a higher-priority token (HPT) and a lower-priority token (LPT) circulate around the ring whenever all stations are idle. The operation of the HPT is not affected by the existence of the LPT while an LPT user is required to stop transmission upon sensing a busy HPT. We show that the presented method results in a substantial saving in time delay caused by token passing, especially when the system traffic is light. In addition, the presented double-token access protocol has an inherent feature of automatic token recovery in case of a single token loss and thus greatly improves the reliability of token ring networks.