TCP mechanisms for improving the user experience for time-dependent thin-stream applications

A wide range of Internet-based services that use reliable transport protocols display what we call thin-stream properties. This means that the application sends data with such a low rate that the retransmission mechanisms of the transport protocol are not fully effective. In time-dependent scenarios where the user experience depends on the data delivery latency, packet loss can be devastating for the service quality. In order to reduce application-layer latency when packets are lost, we have implemented modifications to the TCP retransmission mechanisms in the Linux kernel. The changes are only active when thin-stream properties are detected, thus not affecting TCP behaviour when the stream is not thin. In this paper, we show the latency improvements from these thin-stream modifications. We have tested several thin-stream applications like remote terminals (SSH) and audio conferencing (Skype), and we evaluate the user experience with and without the TCP modifications. Our experimental results show that our modifications allow TCP to recover earlier from packet loss. Furthermore, user surveys indicate that the majority of users easily detect improvements in the perceived quality of the tested applications.