Multicasting of adaptively-encoded MPEG4 over QoS-aware IP networks

We propose a novel architecture for multicasting adaptively-encoded layered MPEG4 over a QoS-aware IP network. We require such a network to (1) support priority dropping of packets in time of congestion; (2) provide congestion notification to the multicast sender. For the first requirement, we use RED´s extension for service differentiation. It recognizes the priority of packets and drops lower priority packets first. We couple RED (random early detection) with our proposal for the second requirement which is the adoption of backward explicit congestion notification (BECN). BECN provides early congestion notification at the IP layer level to the video sender. BECN detects upcoming congestion based on size of the RED queue in the routers. The MPEG4 adaptive-encoder can change the sending rate and divide the video packets into lower priority packets and high priority packets. Based on BECN messages from the routers, a simple flow controller at the sender sets the rate for the adaptive MPEG4 encoder and also sets the ratio of the high priority and low priority packets within the video stream. We use a TES model for generating the MPEG4 traffic that is based on real video traces. Simulation results show that combining priority dropping, MPEG4 adaptive encoding and multicast BECN: (1) improves bandwidth utilization; (2) reduces the time to react to congestion and hence improves the received video quality; (3) maintains graceful degradation in quality with congestion and provides minimum quality even if congestion persists.