An analysis of the performance, in terms of average message delay, is presented for a system of interconnected ring networks. The system is hierarchical, with local rings served by a high-speed backbone ring through gateway queues. In both the local and the backbone rings, the access technique employed is token passing. Service disciplines, with and without priority, have been studied. In the former, priority is given to inter-ring traffic over local traffic. The study makes use of certain results on average delay in systems where the customer initiating a busy period receives special service for the M/G/1 queue with nonpreemptive priority and for the G/G/1 queue. The analysis, which involved several approximations, was verified by simulation.>

A LAN or MAN (local or metropolitan area network) using token passing to allow stations to access the transmission medium is studied. Ibe and Cheng (1989) recently presented an approximate derivation of message delays for an asymmetric single-service token passing with only one type of message. In the present work, this analysis is extended to an operation with nonpreemptive priority queuing. The number of message priority levels and the walktime vary from one station to another. Moreover, the assumed Poisson message arrival process and the message transmission time vary, not only from one station to another, but also from one class to another. The performance, as measured by the mean delay for any message class at any station, is derived. The simulation results show excellent agreement with the analytical results, even under heavy loading. The results confirm earlier findings that the performance at a station is influenced by its position relative to heavily loaded stations.>