Performance of token schemes supporting delay-constrained priority traffic streams

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 concentration. 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 the IEEE 802.5 token-ring-type protocol), that no high-priority messages are currently waiting in the system. Two token schemes employing different service disciplines are used to provide network access. Exact and approximate mean delay formulas for both message classes are derived. Numerical results are then exhibited to illustrate the network performance under various traffic conditions