Enhancing TCP Performance in Hybrid Networks with Fixed Senders and Mobile Receivers

Transmission control protocol (TCP) plays an important role in defining a network's performance. Its use in wireless networks has exposed several inadequacies in its operation. We propose an improvement over TCP for communication between fixed host (FH) senders and wireless, mobile host (MH) receivers that are interlinked by base stations (BS). We believe that this is becoming the main infrastructure supporting most mobile Internet traffic. Our new scheme is called TCP-ECN (explicit congestion notification). It aims to address the challenges of high bit error rate in wireless links and long disconnections due to mobility. It keeps the modification in BS and MH minimal without requiring any changes to FH. The BS uses one bit (ECN bit) to enable the MH in distinguishing between congestion and wireless losses, and thus, suppressing unnecessary duplicate acknowledgments (dupACK) due to wireless losses. In addition, zero window acknowledgment and triplicate dupACK schemes are adopted as part of the handoff procedure in BS. Both simulation and network test-bed results show that TCP-ECN performs significantly better than TCP-Reno and Snoop in the face of high wireless loss, high or low congestion loss, and mobility. Performance improvement is more significant when more wireless receivers are supported. We believe this work is significant to wireless carriers and vendors when designing protocols and devices that support mobile Internet access.