Synchronous messages are usually generated periodically and each of them is required to be transmitted before the generation of the next message. Due to the inherent deficiency in its medium access control (MAC) protocol, an FDDI token ring can use at most one half of its ring bandwidth to transmit such synchronous traffic. This deficiency greatly reduces the FDDI's capability of supporting multimedia applications like real-time voice/video transmissions. In this paper, we show how a few simple modifications to the FDDI's MAC protocol can remove this deficiency and double a ring's ability of supporting synchronous traffic. The modified protocol, called FDDI-M, can also achieve a higher throughput for asynchronous traffic than the standard FDDI and the FDDI-II, thus making it useful even for those networks without heavy synchronous traffic.
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