Achieving end-to-end delay bounds by EDF scheduling without traffic shaping

Abstract

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, per-node traffic shaping has been believed to be necessary. However, shaping introduces artificial packet delays. 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 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 best-effort 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.