Upper Bounds for the Token Rotation Time in the 802.4 Token -Passing Bus

A detailed analysis of the cycle time properties of the IEEE 802.4 token bus protocol is presented. It is shown that its average token rotation time (TRT) is upper bounded by Ta, i.e. the maximum of the TRTs regulating the asynchronous transmissions. It is also shown that the token rotation time is upper bounded by (T a+H), where H is the sum of all high-priority token holding times (HPTHTs) of the synchronous queues of the network. These bounds are useful when studying the characteristics of responsiveness of an IEEE 802.4 network, so as to meet the delivery deadlines and the expiration times of the synchronous messages generated at different stations