Two-way TCP traffic over rate controlled channels: Effects and analysis
We study the performance of bidirectional TCP/IP connections over a network that uses rate-based dow and congestion control. An example of such a network is an asynchronous transfer mode (ATM) network using the available bit rate (ABR) service, The sharing of a common buffer by TCP packets and acknowledgment tacks) has been known to result in an effect called ack compression, where acks of a connection arrive at the source bunched together, resulting in unfairness and degraded throughput. It has been the expectation that maintaining a smooth flow of data using rate-based how control would mitigate, if not eliminate, the various forms of burstiness experienced with the TCP window flow control. However, we show that the problem of TCP ack compression appears even while operating over a rate-controlled channel, although the queues are primarily at the end systems now. 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. By analyzing the periodic bursty behavior of the source LP queue, we derive estimates for the maximum queue size and arrive at a simple predictor for the degraded throughput, applicable for relatively general situations. We validate our analysis using simulation on an ATM network using the explicit rate option of the ABR service. We show that the analysis predicts the behavior of the queue and the throughput degradation not only in simple configurations, but also in more general situations, such as multiple synchronized connections between a pair of end systems, multiple end systems having different round-trip delays, and in configurations with significant amounts of cross-traffic.
rate control congestion control tcp over atm two-way traffic