Workconserving vs. Non-workconserving Packet Scheduling: an Issue Revisited

Many packet schedulers for QoS networks are equipped with a rate control mechanism. The function of a rate control mechanism (rate controller) is to bu er packets from ows which exceed their negotiated tra c pro le. It has been established that rate controllers lead to reduced bu er requirements at packet switches, and do not increase the worst-case delays in a deterministic service. On the other hand, rate controllers make a scheduler non-workconserving, and, thus, may yield higher average end-to-end delays. In this study, we show that by properly modifying a rate controller, one can design a scheduler which balances bu er requirements against average delays. We present a scheduler, called Earlinessbased Earliest Deadline First (EEDF), which achieves such a balancing using a tunable rate control mechanism. In simulation experiments, we compare EEDF with a rate-controlled EDF scheduler and a workconserving version of EDF.