Performance evaluation of the IEEE 802.4 token bus protocol for distributed real-time applications

A simulation study of the performance of the dynamic token-passing bus access method, designed for real-time local area network applications, is presented. Using software simulation the author investigates the basic question of whether the IEEE 802.4 token bus protocol, through the use of the timed token rotation priority mechanism, guarantees an upper bound on the channel access delay of the highest-priority queues. It is shown that the interactions of the dynamic polling scheme and the timed token rotation service mechanism are influenced by the transient response of the dynamic polling scheme and can potentially lead to the case of channel underutilization. Having demonstrated the protocol's capability of handling asymmetric loads, the author investigates the extent to which the capability is affected by the service discipline used