REFWA plus: enhancement of REFWA to combat link errors in LEO satellite networks

As a distinguished characteristic of satellite environments, high bit error rates (BER) impair the performance of the transmission control protocol (TCP) over satellite networks. In this paper, an error recovery mechanism is proposed to further improve the performance of the recursive, explicit, and fair window adjustment (REFWA) scheme [T. Taleb et al., Feb 2004] [T. Taleb et al., June 2004] in satellite IP networks. The proposed mechanism is called REFWA plus. The fundamental challenge in loss recovery over satellite networks consists in distinguishing between congestion induced packet drops from those due to link errors. In the proposed mechanism, this distinction is based on comparison of the new and old values of the explicit congestion feedback signaled by the REFWA scheme to TCP senders. Effectively, a packet drop due to network congestion is likely to be preceded by a decrease in the computed feedback, whereas packet drops that are followed by an increased feedback are likely to be due to link errors. A set of simulations is conducted to evaluate the performance of the REFWA plus scheme. Simulation results demonstrate that compared to TCP Newreno, TCP Westwood, and REFWA, the proposed scheme improves the system fairness and makes better utilization of the bottleneck link even in environments with high bit error rates.