Token Bus Standard under Heavy Load

It has become clear in the last few years that there is a trend towards integrated digital services. P d e l to the development of public Integrated Services Digital Network (ISDN) is service integration in the local area (e.g. a campus, a building, an aircraft). The types of services to be integrated depend very much on the specific local environment. However, applications tend to generate data t&c belonging to one of two classes. According to IEEE 802.4 terminology, the first major class of traffic is termed synchronous, such as packetized voice and data generated from other applications with real-time constraints, and the second c ias is cdied asynchronous which includes most computer data traffic such as file transfer or facsimile. In this report, we examine the IEEE 802.4 token bus protocol which has been designed to support both synchronous and asynchronous traffic. The protocol is basically a timercontrolled token bus access scheme. By a suitable choice of the design parameters, it can be shown that access delay is bounded for synchronous traffic. As well, the bandwidth allocated to asynchronous traffic can be controlled. We present a throughput analysis of the protocol under heavy load with constant channel occupation of synchronous traffic and constant token-passing times.