Evaluation of TCP retransmission delays
Espen Søgård Paaby · NORA - Norwegian Open Research Archives · 2006
Many applications today (e.g., game servers and video streaming servers) deliver time-dependent data to remote users. In TCP based systems, retransmission of data might give high and varying delays. In applications with thin data streams (e.g., interactive applications like games), the interaction between game players raises stringent latency requirements, and it is therefore important to retransmit lost or corrupted data as soon as possible. In the current version of the Linux kernel (2.6.15), several variations of TCP are included. In this thesis, these variations are compared, tested and evaluated with respect to retransmission latency in different and varying RTT and loss scenarios. The variations are tested for thin and thick data streams, respectively. Thick streams transmit as much data as possible, while the thin streams only need to transfer a small amount of data every once in a while, thus potentially having considerable time intervals between the sending of a few packets. Due to poor performance experienced for the TCP variations in the thin stream part of the tests, several enhancements are proposed, implemented and tested for use in thin stream scenarios. The loss detection mechanisms of TCP do not perform adequately in a thin stream scenario, resulting in high and varying retransmission delays, something which might violate the stringent latency requirements of interactive games. The implemented enhancements provide considerable improvements in the retransmission delay, reducing both the level and the variation of the retransmission delay values.