An analysis of symmetric polling systems with two priority classes

Abstract

A cyclic multiqueue system consists of several stations in which messages are enqueued for transmission, and which are served sequentially in cyclic order by a single server. The arrivals at each queue are independent Poisson processes, and the transmission times are generally distributed. Moreover, there is a nonzero switchover time from one station to the next, which is also generally distributed. Messages can be at either of two priority levels: priority 1 (low) or priority 2 (high), and polling occurs either at low priority, in which case both priority 1 and priority 2 messages can be transmitted, or at high priority, in which case only priority 2 messages are transmitted. The service disciplines considered are the exhaustive service discipline and the gated service discipline. In both cases the performance, as measured by the expected delay for high- and for low-priority messages, is evaluated. Part of the analysis is approximate, and simulation results are presented to validate the approximation.