Finding the minimum available transmission time for the timed token medium access control protocol

Exactly capturing the minimum available time for a network node to transmit its synchronous messages during any given length of time is important for guaranteeing the transmission of synchronous messages before their deadlines in a timed token ring network (such as FDDI) where the timed token medium access control protocol is used. Previous results which only give a lower bound on the minimum transmission time could be too pessimistic for supporting the timely delivery of synchronous traffic in a hard real-time communication environment. This paper presents an O(n)-time algorithm for exactly determining the minimum available transmission time. The algorithm can be used to test whether or not a given allocation of synchronous bandwidths can guarantee a synchronous message set with message deadlines no more than periods; the test so formed is better than any previous testing method whose test is sufficient only, in the sense that it is both sufficient and necessary and therefore optimal.