TCP/IP performance and behavior over an ATM network

As Internetwork Protocol suites are enhanced to effectively carry voice and video as well as data, the performance of TCP/IP over broadband ATM networks becomes a critical issue. The end to end TCP layer performance across an ATM network is influenced by various factors such as the characteristics of the ATM adapters, the bandwidth available for a TCP session, the ATM switch functionality and performance under varying traffic loads and traffic statistics. To explore the influences of these factors, various tests have been performed and insight into the TCP behavior in a 'realistic' congested network environment is gained. The background traffic which limits the bandwidth available for a TCP connection plays a critical role in determining the TCP performance. The burstiness of the background traffic affects the TCP throughput little when the output buffer in the ATM switch is large (such as 8000 cell space.) The early packet discard (EPD) function in the switch can improve the throughput significantly when the congestion condition of the TCP connection is moderate. The traffic shaping function in the adapter can push the capacity utilization to about 100% regardless of the bandwidth available for the TCP connection.