Achieving End-to-end Delay Bounds by EDF Scheduling without Traffic Shaping

Earliest Deadline First scheduling with per-node traffic shaping (RC-EDF) has the largest schedulable region among all practical policies known today and has been considered a good solution for providing end-to-end packet delay bounds. In order to harness the traffic burstiness inside a network to satisfy the schedulability condition of EDF, pernode traffic shaping has been believed to be necessary. However, shaping introduces artificial packet delays. In this paper, we show that by deadline assignments at each node that are strict time-shifting of the source packet arrival times, the functionality of shaping can be implicitly realized; the resulting schedulable region of the new scheduling policy is as large as that of RC-EDF. We name the new policy as deadline-curve based EDF (DC-EDF). Not only working in a natural work-conserving way, when the global schedulability condition fails DC-EDF will also work in a “besteffort” way to allow packets excessively delayed at previous nodes to catch up and meet the end-to-end delay bounds. Therefore, DC-EDF is likely to provide “tight” statistical delay bounds. We also prove that a known EDF policy without traffic shaping also has a schedulable region as large as that of RC-EDF.