On Queue Provisioning, Network Efficiency and the Transmission Control Protocol

Authors: Robert N. Shorten, Douglas J. Leith

Complete Citation

Robert N. Shorten and Douglas J. Leith. On Queue Provisioning, Network Efficiency and the Transmission Control Protocol. IEEE/ACM Transactions on Networking, Volume 15, Issue 4, Aug. 2007 Page(s):866 - 877. DOI=10.1109/TNET.2007.893879

Abstract

In this paper, we propose a sender side modification to TCP to accommodate small network buffers. We exploit the fact that the manner in which network buffers are provisioned is intimately related to the manner in which TCP operates. However, rather than designing buffers to accommodate the TCP AIMD algorithm, as is the traditional approach in network design, we suggest simple modifications to the AIMD algorithm to accommodate buffers of any size in the network. We demonstrate that networks with small buffers can be designed that transport TCP traffic in an efficient manner while retaining fairness and friendliness with standard TCP traffic.

Annotations

The typical rule of thumb in the design of router buffers is to provision the buffer to be equal to DBP (Delay-Bandwidth Product). But this rule is difficult to follow physically in high delay-bandwidth networks.

An alternative strategy for buffer provisioning is to exploit statistical multiplexing effects of packets arriving at network buffers to justify arguments in favor of smaller buffer sizes. However, this strategy depends on the assumption that the buffer of interest serves a large number of flows at any instant time.

This paper proposed a sender side modification of TCP AIMD algorithm to accommodate buffers in the network. Use Beta to represent the degree of TCP backoff when a congestion occurs (cwnd_new = Beta * cwnd). For traditional TCP, Beta=0.5. In the proposed scheme:

• If the buffer size of the bottleneck is large, Beta is small. As there are enough packets in the buffer, even if TCP backoffs a lot, the link still can receive high utilization.
• If the buffer size of the bottleneck is small, Beta is large. For a small buffer size, TCP has to backoff conservatively to avoid low link utilization. For a buffer size equal to 0.25*DBP, Beta=0.8 ensures a high link utilization.

-- YingxinJiang - 26 Sep 2007