Optimizing TCP loss recovery performance over mobile data networks

Recent advances in high-speed mobile networks have revealed new bottlenecks in ubiquitous TCP protocol deployed in the Internet. In addition to differentiating non-congestive loss from congestive loss, our experiments revealed two significant performance bottlenecks during loss recovery phase: flow control bottleneck and application stall, resulting in degradation in QoS performance. To tackle these two problems we firstly develop a novel opportunistic retransmission algorithm to eliminate the flow control bottleneck, which enables TCP sender to transmit new packets even if receiver's receiving window is exhausted. Secondly, the application stall can be significantly alleviated by carefully monitoring and tuning the TCP send buffer growth mechanism. We implemented and modularized the proposed algorithms in the Linux kernel thus they can plug-and-play with the existing TCP loss recovery algorithms easily. Using emulated experiments we showed that with the proposed optimization techniques the existing loss recovery algorithms can at most achieve 98.3% bandwidth utilization during loss recovery phase, and reduce RTT by at most 80% after loss recovery phase.