Intelligent Packet Discard Policies for Improved TCP Queue Management

A. Kantawala and J. Turner (USA)


Buffer management, TCP, IP Networks


Recent studies have shown that suitably-designed packet discard policies can dramatically improve the performance of fair queueing mechanisms in internet routers. The Queue State Deficit Round Robin algorithm (QSDRR) preferen tially discards from long queues, but introduces hysteresis into the discard policy to minimize synchronization among TCP flows. QSDRR provides higher throughput and much better fairness than simpler queueing mechanisms, such as Tail-Drop, RED and Blue. However, because QSDRR dis cards packets that have previously been queued, it can sig nificantly increase the memory bandwidth requirements of high performance routers. In this paper, we explore alter natives to QSDRR that provide comparable performance, while allowing packets to be discarded on arrival, saving memory bandwidth. Using ns-2 simulations, we show that the revised algorithms can come close to matching the per formance of QSDRR and substantially outperform RED and Blue. Given a traffic mix of TCP flows with different round-trip times, longer round-trip time flows achieve of their fair-share using the revised algorithms, compared to under RED and Blue. We observe a similar im provement in fairness for long multi-hop paths competing against short cross-traffic paths. We also show that these al gorithms can provide good performance, when each queue is shared among multiple flows.

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