AN INVESTIGATION INTO SHORT-LIVED TCP CONNECTIONS

IP networks are currently experiencing rapid growth in both their capacities and the volume of traffic due increasing usage of the Internet and other HTTP based applications. HTTP traffic is characterised by small and brief transfers of data, these are known as short-lived connections; between these connections long periods of inactivity, the users "think time", occur. To improve the performance of Internet traffic, an improved understanding of short-lived connections which constitute the bulk of the traffic is required. This investigation proposes a method of improving the performance of TCP based, short-lived connections, such as connections utilising HTTP. The main outcome of this project is the proposal of the Super Fast Retransmit algorithm which successfully improves connection performance. This algorithm utilises the correlation between the round trip time for the threeway handshake, and subsequent measurements of the round trip time in order to reduce the overall duration of the data transfer. By utilising these observations, the algorithm is able to pre-empt the signs of a packet loss and retransmit the affected data before standard TCP implementations such as TCP Reno would be able to detect and correct the loss. To establish the correlation in round-trip times, a number of paths were passively monitored using captured TCP traffic, and the packet flows recorded. The collected data was then analysed, initially to establish the time scales for which the characteristics of the path, such as throughput and delay, appear constant. Finally, a range of investigations attempted to establish any correlations between the parameters which were observed. Following the proposal of the retransmission algorithm and a proof of concept implementation, simulations were performed to allow evaluation of the performance improvements. In summary, it was found that the use of the algorithms provided performance increases of approximately 10% to the average completion time of HTTP connections that typically represent short-lived connections under the simulated network conditions.School of Computing, Communications and Electronic