Size-Distortion Optimized Proxy Caching for Robust Transmission of MPEG-4 Video

Abstract

Video delivery over unreliable networks and across error-prone environements suffers a lot from packet loss. several error control techniques have been proposed to deal with this problem. However, retransmission, which achieves highest reliability, was judged as being not feasible for real-time applications. In this work, we propose the deployment of video proxy-caches for error control purposes. Video packets are classified by the sender according to their importance for the decoding process and the perceived video quality. This information is then carried within each packet. Proxy-caches, which are typically located within the network and at access points to lossy networks (e.g. mobile networks), identify valuable video packets and cache them for short periods of time. The receivers can direct their retransmission requests to the proxy caches located in their neighborhood. Furthermore, we develop new cache replacement techniques, based on distortion optimization theory, for operation under strong storage constraints. We show, through simulations and experimental results, important quality improvements compared to conventional sender-based retransmission mechanisms and other cache replacement techniques.