Cycle-Time Properties of the Timed Token Medium Access Control Protocol

Guaranteeing message deadlines is a key issue in distributed real-time applications. The timed token medium access control (MAC) protocol is suitable for real-time application due to its important timing property of bounded channel access time which provides a necessary condition to ensure that the message deadlines are satissed. The inherent timing properties of the timed token protocol that are necessary to guarantee synchronous message deadlines in a timed token ring network such as the Fiber Distributed Data Interface (FDDI) network are investigated, and as a result, a generalized result on the cycle-time properties is found. In particular, an upper bound on the time possibly elapsed between the token's l th arrival at any node i and the to-ken's (l+v) th arrival at any node k (where v is a non-negative integer) is derived. This result, which is particularly important for studies on real-time communications in any timed token ring network, is better than any previously published in the sense that the upper bound derived in this report is more general and tighter. This report presents a concise formal proof for the generalized upper bound.