Performance of token ring protocols for real-time message transmission

We study the average case performance of three token ring protocols through simulation. The first is the token passing protocol which does not adhere to the EDF policy but has a minimal overhead. The second is a modified priority-driven protocol which only approximates the EDF policy with a moderate overhead. The third is the window protocol which implements the exact EDF policy, but its contention overhead might be potentially high. It is found that under the current network technology, the window protocol achieves the best performance in supporting urgent real-time messages. We have also noted that when the ring gets faster, the difference in the performance of the three protocols is reduced. Therefore, the average case performance of a real-time protocol is determined by both the transmission policy employed and the contention overhead incurred.