The nonoptimality of synchronous bandwidth allocation schemes for the timed token protocol

This letter examines the optimality of three published "optimal" synchronous bandwidth allocation (SBA) schemes for guaranteeing synchronous message deadlines with the timed token medium access control protocol. It is found that none of these three schemes is optimal. The nonoptimality has been demonstrated by a numerical example and the root cause has been indicated. The development of an optimal SBA scheme remains a challenge.