An Empirical Study of TCP/IP Performance Over ATM

This paper outlines some basic performance characteristics of the Transmission Control Protocol Internet Protocol TCPIP over Asynchronous Transfer Mode ATM. It also discusses a few solutions to assure acceptable TCPIP performance over ATM which are implemented by the industry the during the last couple of years. The conclusions in this paper are based on empirical TCPIP performance test results collected on a DS3 ATM research testbed, architected with commercially available IP and ATM equipment. TCPIP performance can vary widely and suffer significantly over ATM networks with large Bandwidth Delay products. First, it is essential that the TCP window size matches the Bandwidth Delay product of the end-to-end connection to fully utilize the bandwidth provided by the broadband network. Even if the window size meets this criteria, TCP performance can still be unacceptable, especially if the buffering within the ATM network is limited. A single limited-buffer bottleneck is sufficient to degrade the performance of a TCP connection when multiple traffic sources congest the bottleneck resource, such as in ATM networks with small buffer switches. One approach to assure acceptable TCPIP performance is to limit the data rate into the bottleneck resource by exercising rate control at the entry to the ATM network. A better solution is to provide sufficient buffering within the ATM network.