Performance of local area network protocols for hard real-time applications

Simulation experiments show that the token ring protocol gave a lower average message delay at low transfer rates, but the token bus protocol gave a better overall performance for applications where only average delay is of interest. On the other hand, in hard real-time systems, the criterion of importance is not the average message delay, but the maximum message delay and ability to meet deadlines. Slotted ring in this case is a much better protocol than the others because of its low maximum message delay and more predictable message delay. Because of this, and because the average performance of the slotted ring remains good as the size or the transfer rate of the network increases, the slotted ring protocol is preferred over the token ring and token bus protocols for hard real-time systems.