An Analytical Comparison of the Slow-but-Steady and Impatient Variants of TCP New Reno

Current standard defines two variants of TCP NewReno: the Slow-but-Steady and Impatient. While the behavior of various TCP implementations has been extensively studied over the last years, little attention has been paid to performance analysis of different variants of TCP NewReno. In this paper, we first develop an analytical model of the Impatient variant, which being combined with the earlier proposed model of the Slow-but-Steady variant gives a comprehensive analytical model of TCP NewReno throughput. We then make an analytical comparison of the Impatient and Slow-but-Steady throughputs in the presence of correlated losses. We show that, although neither of the two variants is optimal, the Impatient variant provides the same throughput as the Slow-but-Steady one in a wide range of network conditions and significantly outperforms it in case of large windows and multiple packet drops. This could be of special interest for networks with large bandwidth and long delay.