Analysis for token ring networks operating under message priorities and delay limits

A symmetric priority-based token network is considered. Messages are divided into two priority classes. High-priority messages are assumed to require tight delay constraints. As a result, each station is allowed to establish, at any time, at most a single real-time high-priority access connection. High-priority messages are guaranteed access onto the channel within a prescribed limited period. In turn, regular priority messages are only served when the system determines, through the repetitive use of circulating tokens, (as used by IEEE 802.5 token ring type protocol) that no high-priority messages are currently waiting in the system. Two token schemes, using different service disciplines, are used to provide network access. Exact mean delay formulas for both message classes are derived. Approximate message delay analysis approaches are also investigated for networks containing large numbers of stations. Numerical results are then exhibited to illustrate the network performance under various traffic conditions