Deadline aware packet scheduling in switches for multimedia streaming applications

Abstract

We consider the problem of scheduling packets in an input queued switch with a focus on processing streamed multimedia data. In such applications, packets arrive with hard service deadlines; after the deadline for a packet has passed, it is no longer useful and does not get delivered -it is dropped. We seek policies to minimize the number of late packets, which are then dropped. The problem is formulated in a Dynamic Programming framework and shown to be intractable. The formulation is contrasted to the related crossbar switch scheduling problem, with an emphasis on the fact that we have a different objective function. A simplified probabilistic version of the streaming problem is used as motivation for a heuristic solution. Finally, we present results from a simulation in which a simple heuristic based on weighting queues according to the deadline of the leading packet consistently outperforms the wellknown maximum weight matching (MWM) algorithm.Index Terms-scheduling; deadlines; crossbar switch; inputqueued switch; maximum weight matching I. INTRODUCTIONIn this paper we consider the problem of moving data packets from a set of input ports to a set of output ports with the special provision that packets carry a deadline for delivery. Such a constraint appears in applications where the data are processed in a real-time streaming fashion; instead of incurring additional delay beyond a specified deadline, it is preferable to drop the late packet and move on to the next one. This appears frequently in the context of Voice over IP (VoIP), Video over Broadband (VoBB), Video on Demand (VoD) and a host of other applications in which delay beyond a specified threshold is no longer acceptable.Results for queuing problems involving packet deadlines appear frequently in the multimedia streaming and wireless communications literature. In [1], the problem of scheduling multiple queues in which streaming packets have deadlines over a wireless channel is considered, but there are not multiple output queues. The analysis in [2] examines policies that are simultaneously aware of channel strength, packet deadlines and distortion and [3] looks at scheduling packets at a base station to maximize quality of service to downlink users where deadlines play a role in the quality. Policies for multicast routing with similar loss criteria and packet constraints are studied in [4]. Packet deadlines as well as packet values are considered in [5] for a single queue, and bounds on the competitive ratio are derived.