EDD algorithm performance guarantee for periodic hard-real-time scheduling in distributed systems

In this paper we investigate the worst case performance of Earliest Due Date algorithm when applied to packet scheduling in distributed systems. We assume that the processing elements communicate via a multistage interconnection network, and that the system is synchronous. When two or more packers are simultaneously sent over the same input port, or received through the same output port, the packets undergo a collision and are damaged, needing to be retransmitted later. This causes a performance degradation in terms of both throughput and delay. So, collisions must be avoided. The special type of traffic to be scheduled by Earliest Due Date is a periodic hard-real time one, and the objective is to schedule all the packers within their individual due dares. We establish that EDD is always able to produce a schedule meeting this objective, whenever the so called link utilization is no more than 1/2, showing that this worst case performance bound is tight. Such a bound can be effectively used as a feasibility test before actually running the algorithm.