Enhancing TCP performance in networks with small buffers

Abstract

TCP performance can be significantly affected when the buffer capacity at routers is small. This is possible when either many flows share the network or the bandwidth-delay product is large (e.g. satellite links). The behavior of various versions of TCP with respect to buffer capacity issues has not been studied in much detail. We investigate the behavior and performance of different TCP variants under small buffer capacity conditions. We recognize TCP pacing as a potential solution. However, instead of using TCP's sending rate as the dictating metric, we make use of the bandwidth-share estimate (BSE), maintained by TCP Westwood, to set the pacing interval. We call this newly proposed protocol paced-Westwood. We also show the need to scale BSE further to mitigate the effects of positive feedback in BSE. For this, we propose a further enhancement that we call /spl alpha/-paced Westwood that uses a scaling parameter /spl alpha/ to enforce convergence of BSE and the pacing interval. The proposed /spl alpha/-paced Westwood uses its BSE to space the packet bursts during the slow-start phase, resulting in a superior throughput in the troublesome low buffer capacity cases. With the help of simulations, we show that our enhanced TCP Westwood outperforms both unpaced as well as paced TCP NewReno under low buffer capacity networks.