Performance evaluation of a bandwidth allocation scheme for guaranteeing synchronous messages with arbitrary deadlines in an FDDI network

We study the performance of FDDI networks in terms of their guarantee probability, i.e., the probability that a set of synchronous messages are guaranteed to meet their deadlines. Traditional techniques such as queuing analysis cannot be directly used to derive the guarantee probability. To counter this problem, we develop a new geometric model of schedulability. Based on this model, we obtain a numerical method to compute the exact values of the guarantee probability. A closed-form approximation for the guarantee probability is also derived, and is shown to be relatively accurate and computationally efficient. The network performance is then systematically examined in terms of the guarantee probability. We find that there is a high probability that a randomly chosen message set can be guaranteed even when the real-time traffic is increased beyond the worst case achievable utilization bound. Hence, FDDI networks are applicable for real-time applications in a wide range of loading conditions