Second-Order Rate-Control Based Transport Protocols Over Mobile Wireless Networks

Abstract

While TCP (transmission control protocol) is an efficient transport protocol in the wired Internet, it performs poorly when used in wireless environments. This is because TCP couples the error and flow control by using packet loss to infer the network congestion and thus the random loss in wireless Internet can inevitably mislead TCP dropping its flow-control window unnecessarily, even if the network is not congested at all. To overcome this problem, we propose the second-order rate-based flow control and the decoupled window-based error-control schemes for high-throughput transport protocols over the wireless networks. The second-order rate control minimizes congestive losses by using the explicit congestion notification (ECN)-bit feedback to adapt the rate-gain parameter to the variations of the round-trip time (RTT) and cross-traffic flows. The error-control scheme detects and selectively retransmits the lost packets caused by either congestion or random-noise/handoffs on wireless links, which is decoupled from the flow control such that the rate control is independent of the random loss of wireless links. Using the fluid analysis, we establish the rate-control model, and derive expressions for throughput, losses, and link-transmission efficiency. Through extensive simulations, the proposed transport protocol is shown to possess the TCP-compatibility in bandwidth while coexisting with TCP-Reno traffics in the wired Internet. Our simulations also verify the analysis, and demonstrate the significant superiority of our scheme to TCP in terms of increasing the average throughput over wireless links and the robustness to the variation of wireless random-loss probability while minimizing the losses and retransmissions.