Understanding the performance of many TCP flows

As the most widely used reliable transport in today’s Internet, TCP has been extensively studied in the past decade. However, previous research usually only considers a small or medium number of concurrent TCP connections. The TCP behavior under many competing TCP flows has not been sufficiently explored. In this paper 1, we use extensive simulations to systematically investigate the performance of a large number of concurrent TCP flows. We start with a simple scenario, in which all the connections have the same round-trip time, and the gateways use Drop-Tail policy. We examine how the aggregate throughput, goodput, and loss rate vary with different underlying topologies. We also look at the behavior of each individual connection when competing with other connections. We observe global synchronization in some cases. We break the synchronization by either adding random processing time or using RED gateways, and examine their effects on the TCP performance. Finally we investigate the TCP performance with different RTT’s, and quantify the roundtrip bias using both analysis and simulations.