Best Effort and Priority Queuing Policies for Buffered Crossbar Switches

The buffered crossbar switch architecture has recently gained considerable research attention. In such a switch, besides normal input and output queues, a small buffer is associated with each crosspoint. Due to the introduction of crossbar buffers, output and input contention is eliminated, and the scheduling process is greatly simplified. We analyze the performance of switch policies by means of competitive analysis, where a uniform guarantee is provided for all traffic patterns. The goal of the switch policy is to maximize the weighted throughput of the switch, that is the total value of packets sent out of the switch. For the case of unit value packets (Best Effort), we present a simple greedy switch policy that is 4-competitive. For the case of variable value packets, we consider the Priority Queueing (PQ) mechanism, which provides better Quality of Service (QoS) guarantees by decreasing the delay of real-time traffic. We propose a preemptive greedy switch policy that achieves a competitve ratio of 18. Our results hold for any value of the switch fabric speedup. Moreover, the presented policies incur low overhead and are amenable to efficient hardware implementation at wire speed. To the best of our knowledge, this is the first work on competitive analysis for the buffered crossbar switch architecture.

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