Guaranteeing synchronous messages with arbitrary deadline constraints in an FDDI network

This paper addresses issues related to guaranteeing synchronous messages with arbitrary deadline constraints in an FDDI network. We show that several network parameters must be set carefully if message deadlines are to be satissed. First, message deadlines can only be met if suucient synchronous bandwidth is allocated to each node. Thus, proper synchronous bandwidth allocation is essential if deadlines are to be guaranteed. Second, the target token rotation time (TTRT) determines both the speed of token circulation and the network utilization available to user applications. TTRT should also be chosen carefully to ensure that the token circulates fast enough while maintaining a high available utilization. Finally, suucient buuer space must be provided for outgoing messages, otherwise messages could be lost due to buuer overrow. In this paper, we propose and analyze an integrated method for allocating the synchronous bandwidth and selecting TTRT so that the time constraints of synchronous messages with arbitrary deadlines are guaranteed to be met. Our method diiers from previous work by taking into account both message periods and message deadlines. As a result, the network's capability for guaranteeing real-time messages is increased dramatically. Furthermore, we derive an upper bound for the maximum message waiting time. This gives an upper bound for the required buuer size. We show that this bound is independent of message deadlines | giving considerable exibility to applications in choosing message deadlines.