Priority Queue Schedulers with Approximate Sorting in Output Buuered Switches

All recently proposed packet scheduling algorithms for output-bu ered switches which support QoS transmit packets in some priority order, for example, according to deadlines, virtual nishing times, eligibility times, or other timestamps that are associated with a packet. Since maintaining a sorted priority queue introduces signi cant overhead, much emphasis of QoS scheduler design is put on methods to simplify the task of maintaining a priority queue. In this study, we consider an approach which approximates a priority queue at an output bu ered switch. The goal is to trade o less accurate sorting for lower computational overhead. Specifically, this paper presents a scheduler which approximates the sorted queue of an EarliestDeadline-First (EDF) scheduler. The approximate scheduler is implemented using a set of prioritized FIFO queues which are periodically relabeled. The scheduler can be e ciently implemented with a xed number of pointer manipulations, thus, enabling an implementation in hardware. Necessary and su cient conditions for the worst-case delays of the scheduler with approximate sorting are presented. Numerical examples, including traces based on MPEG video, demonstrate that in realistic scenarios, scheduling with approximate sorting is a viable option.