Queue management for short-lived TCP flows in backbone routers

Packets in the Internet can experience large queueing delays during busy periods. Backbone routers are generally engineered to have large buffers, in which packets may wait as long as half a second (assuming FIFO service, longer otherwise). During congestion periods, these buffers may stay close to full, subjecting packets to long delays, even when the intrinsic latency of the path is relatively small. This paper studies the performance improvements that can be obtained for short-lived TCP flows by using more sophisticated packet schedulers, than are typical of Internet routers. The results show that the large buffers found in WAN routers contribute only marginally to improving router throughput, and the higher delays that come with large buffers makes them a dubious investment. The results also show that better packet scheduling algorithms can produce dramatic improvements in fairness. Using ns-2 simulations, we show that algorithms using multiple queues can significantly outperform RED and Blue, especially at smaller buffer sizes. Given a traffic mix of short-lived TCP flows with different round-trip times, longer round-trip time flows achieve 80% of their fair-share using multiqueue schedulers, compared to 40% under RED and Blue. We observe a similar performance improvement for multi-hop paths. We also show that performance results can be reliably scaled across a wide range of parameter values, so long as the ratio of the buffer size to the link bandwidth-delay product is held invariant.