Performance of Paced and Non-Paced Transmission Control Algorithms in Small Buffered Networks

Famous rule-of-thumb states that a buffer sized at B = RTT × BW, where RTT is the average round trip time and BW is the bandwidth of output link is necessary in order to achieve high utilization with TCP flows. However, as the link speeds continue increasing with technological advances, this buffer requirement starts becoming an important cost factor on routers of electronic networks. On the other hand, bursty nature of TCP limits further decreasing the buffer requirements, because it brings a high packet drop rate in small buffered networks. In this paper, we evaluate several transmission control algorithms in small buffered networks. The algorithms include TCP Reno, TCP NewReno, Highspeed TCP with SACK, and XCP. Simulation results show that all non-paced TCP and XCP variants perform poorly. Furthermore, the results show that even rule-of-thumb buffers are not enough for XCP in some cases because of high burstiness of XCP. We evaluate the effectiveness of pacing method at sender side for making transmission control algorithms suitable for very small buffered networks. We show that pacing alone is not enough for XCP to make suitable for small buffered networks, so we introduce a suitable parameter set. Simulation results show that buffer requirements on routers are greatly reduced by paced XCP with suitable parameter settings, while keeping the high fairness, fast convergence, and high utilization.