An integrated model for the latency and steady-state throughput of TCP connections

Most TCP connections in today’s Internet transfer data on the order of only a few kilobytes. Such TCP transfers are very short and spend most of their time in the slow start phase. Thus the underlying assumptions made by steady-state models cease to hold, making them unsuitable for modeling finite flows. In this paper, we propose an accurate model for estimating the transfer times of TCP flows of arbitrary size. Our model gives a more accurate estimation of the transfer times than those predicted by Cardwell et al. [Proceedings of the IEEE INFOCOM, Tel Aviv, Israel, March 2000, pp. 1742–1751], which extends the steady-state analysis of Padhye et al. [IEEE/ACM Trans. Networking 8 (2) (2000) 133] to model finite flows. The main features of our work are the modeling of timeouts and slow start phases which occur anywhere during the transfer and a more accurate model for the evolution of the cwnd in the slow start phase. Additionally, the proposed model can also model the steady-state throughput of TCP connections. The model is verified using web based measurements of real life TCP connections. We also introduce an empirical model which allows a better “feel” of TCP latency and the nature of its dependence on loss probabilities and window limitation. Finally, the paper investigates the effect on window limitation and packet size on TCP latency.