A Study of Timing Properties with the Timed Token Protocol

We investigate the timing properties necessary to guarantee synchronous message deadlines in a token ring network such as FDDI (Fibre Distributed Data Interface) where the timed token medium access control protocol (MCA) is employed. We present a tighter upper bound, than previously published, for the worst case achievable utilisation of the MCA scheme. We also found that, under the condition that the total channel bandwidth available for message transmission is fully/exhaustively allocated among all synchronous message streams, the lower bound of the worst case achievable utilisation with the MCA scheme is a function of the number of nodes in the network. As a result, a tighter lower bound is derived. In addition we propose a similar optimal synchronous capacity allocation scheme named IMCA (Improved MCA) which performs better than the MCA scheme in the sense that it can guarantee not only all synchronous message sets which can be guaranteed by the MCA scheme but also some other synchronous message sets for which the MCA scheme cannot apply. In general the report enhances the results obtained by Zhao et al[Mal93, Che92b, Agr92b].