Optimizing TCP Loss Recovery Performance Over Mobile Data Networks

TL;DR

This paper introduces novel TCP loss recovery algorithms tailored for mobile data networks, significantly enhancing bandwidth efficiency and reducing latency by addressing flow control and application stalls.

Contribution

It proposes a new opportunistic retransmission algorithm and buffer tuning method, implemented in Linux, to improve TCP performance over mobile networks.

Findings

Bandwidth efficiency increased by up to 133%.

RTT spikes completely mitigated, reducing RTT by over 50%.

Algorithms are modular and easily integrated into existing systems.

Abstract

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 the 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, application stall can be significantly alleviated by carefully monitoring and tuning the TCP sending 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, compared to the existing TCP loss recovery algorithms, the proposed optimization algorithms improve the bandwidth efficiency by up to 133% and completely mitigate RTT spikes, i.e., over 50% RTT reduction, over the loss recovery phase.