Achieving high throughput and low delay in mobile data networks by accurately predicting queue lengths

Abstract

Knowledge of the queue length for a radio link in a mobile data network has a significant effect on the performance of the communication protocol TCP. If the queue length can be accurately estimated and regulated to a target value, then low end-to-end delay and high bandwidth utilization can be achieved. One method for estimating and regulating the queue length is the queue-length-based congestion control (QCC) algorithm. However, this algorithm estimates the queue length over one RTT interval prior to transmission, and the actual queue length after that time can differ significantly, because the bandwidth can vary substantially between the neighboring propagation delays, which could result in a false positive in the queue length adaption, thereby affecting the QoS performance. To address this problem, we propose PQ-TCP, a method that predicts the queue length directly by predicting the bandwidth variations over the ensuing period of time equal to the propagation delay and using post-bandwidth analysis to minimize the prediction error. Trace-driven simulations are used to show that the QoS performance of PQ-TCP is superior to that of current QCC algorithms. PQ-TCP achieves the lowest RTT while maintaining nearly 90% bandwidth utilization for a small target queue length of 5 packets.