An Experimental Study of Router Buffer Sizing for Mixed TCP and Real-Time Traffic

Recent research results on Internet router buffer sizing suggest that when TCP traffic is well-paced, Internet routers need as few as 20-30 packet buffers to realise near-maximum link throughputs, independent of link capacities and number of TCP flows. However, these studies have ignored non-TCP traffic, on the grounds that TCP traffic predominates in the Internet. In this paper we evaluate this assumption via practical experiments on a long-haul Australian network. Specifically, for different volumes of long range dependent real-time streaming video traffic in the network, we quantify end-to-end TCP throughput and real-time traffic loss as router buffer sizes at bottleneck and non-bottleneck links vary. Our results indicate that even in the presence of 5-15% bursty real-time traffic, TCP requires larger router buffers to achieve a given fraction of its saturation throughput. However, larger buffers lead to increased losses for real-time traffic. This suggests that TCP and non-TCP traffic can negatively impact each other, and their performance trade-offs need to be considered when sizing router buffers.