Throughput analysis of a timer-controlled token-passing protocol under heavy load

To support real-time applications on a local area network, some recently proposed standards, such as the IEEE 802.4 token bus standard and FDDI, use timers to control station access of the channel in addition to a basic token-passing protocol. The major reason for incorporating the timing mechanism is to avoid excessively long cycles in token-passing that can disrupt real-time services for packetized voice and real-time control. Nevertheless, the timing mechanism is flexible enough to provide priority among non-real-time traffic as well. The authors present an analysis of the throughput performance of the timer-controlled token-passing protocol under heavy load and a few other assumptions. The analysis not only reveals the priority structure of the protocol but also some salient features that render the protocol more favorable than other cycle-limiting schemes (e.g., fixed-maximum channel access per cycle).<>