Stateful-TCP—A New Approach to Accelerate TCP Slow-Start

Abstract

The Transmission Control Protocol (TCP) is one of the pillars of the Internet. Therefore extensive research has been conducted to improve its performance, primarily via optimizing TCP's congestion control algorithm. In this work, we show that besides congestion control, TCP's Slow-Start algorithm is increasingly becoming a bottleneck in modern high-speed networks. To tackle the problem, we propose a different approach called Stateful-TCP, where path bandwidth estimated in a previous flow is used to instantly ramp up the transmission rate of the subsequent flow to the same destination. This eliminates the need for bandwidth probing in conventional Slow-Start, enabling TCP to efficiently utilize the available path bandwidth right from the beginning. We applied Stateful-TCP to Linux's default TCP implementation - Cubic, to form S-Cubic and evaluated its performance via extensive emulations and Internet experiments. Results from independent Internet experiments using over 1,000 end-user clients showed that S-Cubic could reduce FCT by 37.5% and increase throughput by over 50% compared to Cubic. As opposed to an entirely new TCP design, Stateful-TCP is designed to complement congestion control and thus could potentially be applied to many of the existing TCP variants, as well as incorporated into future TCP designs.

Keywords

• TCP
• slow-start
• stateful
• bandwidth estimation