A client-side split-ACK tool for TCP Slow Start investigation

TCP´s Slow Start phase has recently gotten much attention because Google proposes to use a larger starting point (Initial Window, IW). For their large-scale measurement study, they have applied a change to their well-connected web server; how the larger IW would affect other servers, or hosts that would use it to send data across a low-bandwidth or wireless connection, is less understood. We present a tool that, by splitting ACKs into multiple pieces at the beginning of a connection, can be used to trick a host into sending a larger number of packets than normally intended within one RTT in Slow Start. Test results indicate that, while many hosts do not react to our tool, some do - probably enough to use the tool for measurements.