Two-way TCP traffic over ATM: effects and analysis

We examine the performance of bidirectional TCP/IP connections over asynchronous transfer mode (ATM) networks using the available bit rate (ABR) service. The problem of "ack-compression" re-appears, although the queues are primarily at the end-systems. We further the understanding of the problem by quantitatively analyzing the periodic bursty behavior of the source IP queue. We are able to predict the peak values for the queue and arrive at a simple robust predictor for the degraded throughput, applicable for relatively general situations. The degradation in throughput due to bidirectional traffic can be significant. For example, even in the simple case of symmetrical connections with adequate window sizes, the throughput of each connection is only 66.67% of that under one-way traffic. We validate our analysis using simulation, where the ATM network uses the explicit rate option. We show that the analysis predicts the behavior of the queue and the throughput degradation. We observe the need to separate the flow of acknowledgments and data for the bidirectional TCP connection and for inter-leaving their processing at the end-systems to overcome the problem of ack compression.