A Study of Partially Reliable Transport Protocols for Soft Real-Time Applications

The profileration of multimedia applications, such as streaming video, teleconferencing, and interactive gaming has created a tremendous challenge for the traditional transport protocols of the Internet – UDP and TCP. Specifically, many multimedia applications are examples of soft real-time applications. They have often relatively stringent require- ments in terms of delay and delay jitter, but typically tolerate a limited packet loss rate. In recognition of the transport service requirements of soft real-time applications, this thesis studies the feasibility of using retransmission based, partially reliable trans- port protocols for these applications. The thesis studies ways of designing retransmis- sion based, partially reliable transport protocols that are congestion aware and TCP com- patible. Furthermore, the transport protocols should provide a service that, in terms of performance metrics such as throughput, delay, and delay jitter, are suitable for soft real- time applications. The thesis work comprises the design, analysis, and evaluation of two retransmission based, partially reliable transport protocols: PRTP and PRTP-ECN. Extensive simulations have been carried out on PRTP as well as PRTP-ECN. These sim- ulations have in part been complemented by some theoretical analysis. The results of the simulations and the analysis suggest that substantial reductions in delay jitter and improvements in throughput can indeed be obtained with both PRTP and PRTP-ECN as compared to TCP. While PRTP reacted too slowly to congestion to be TCP-friendly and altogether fair, PRTP-ECN was found to be both TCP-friendly and reasonably fair. The thesis work also comprises an extensive survey on retransmission based, par- tially reliable transport protocols. Based on this survey, we have proposed a taxonomy for these protocols. The taxonomy considers two dimensions of retransmission based, partially reliable transport protocols: the transport service, and the error control scheme.