A Client-side Split ACK Tool for TCP Slow Start Investigation

Abstract

The start-up phase in TCP is called Slow Start, and is followed by Congestion Avoidance. The Slow Start phase is becoming a bottleneck of communication in the Internet today. There are several proposals to improve TCP’s Slow Start phase and it has recently gotten much attention because Google proposes to use a larger starting point (Initial Window, IW).

We present a tool that, by splitting acknowledgements of TCP into multiple pieces at the beginning of a connection, to trick a host into quickly sending a larger number of packets than normally intended. We tested the method against different Operating Systems, commercial companies and the top 600 most visited web sites in the world. Test results indicate that, while many hosts do not react to our tool, some do, and they are probably enough to use the tool for measurements.