Understanding the performance of many TCP flows

As the most widely used reliable transport in today's Internet, TCP has bee n extensively studied in the past decade. However, previous research usuall y only considers a small or medium number of concurrent TCP connections. Th e TCP behavior under many competing TCP flows has not been sufficiently exp lored. In this paper, we use extensive simulations to systematically invest igate the performance of a large number of concurrent TCP flows. We start w ith a simple scenario, in which all the connections have the same roundtrip time (RTT), and the gateways use drop-tail policy. We examine how the aggr egate throughput, goodput, and loss rate vary with different underlying top ologies. We also look at the behavior of each individual connection when co mpeting with other connections. We observe global synchronization in some c ases. We break the synchronization by either adding random processing time or using random early detection (RED) gateways, and examine their effects o n the TCP performance. Finally we investigate the TCP performance with diff erent RTTs, and quantify the roundtrip bias using both analysis and simulat ions. (C) 2001 Elsevier Science B.V. All rights reserved.