Implementation and Experimental Evaluation of a Partially Reliable Transport Protocol

Sammanfattning: In the last decade, we have seen an explosive growth in the deployment of multimedia applications on the Internet. However, the transport service provided over the Internet is not always feasible for these applications, since the network was originally designed for other types of applications. One way to better accommodate the service requirements of some of these applications is to provide a partially reliable transport service. A partially reliable transport service does not insist on recovering all, but just some of the packet losses, thus providing a lower transport delay than a reliable transport service. The work in this thesis focuses on the design, implementation, and evaluation of a partially reliable transport protocol called PRTP. PRTP has been designed as an extension to TCP in order to show that such a service could be effectively integrated with current protocol standards. An important feature of PRTP is that all modifications for PRTP are restricted to the receiver side, which means that it could be very easily deployed. The thesis presents performance results from various experiments on a Linux implementation of PRTP. The results suggest that transfer times can be decreased significantly when using PRTP as opposed to TCP in networks in which packet loss occurs. Furthermore, the thesis includes a study that investigates how users perceive an application that is based on a partially reliable service. Specifically, how users select the trade-off between image quality and latency when they download Web pages is explored. The results indicate that many of the users in the study could accept less than perfect image qualityif the latency could be shortened.