Performance Evaluation of a Bandwidth Allocation Scheme for Guaranteeing Synchronous Messages with Arbitrary Deadlines in an FDDI Network

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