Proceedings of the 12 th IEEE International Packet Video Workshop 2002 Pittsburg, PA, April 2002, http://www.pv2002.org (unformatted version) KHAN/GU/ZAGHAL 1 SYMBIOTIC VIDEO STREAMING BY TRANSPORT FEEDBACK BASED QUALITY-RATE SELECTION Javed I. Khan, Qiong Gu and Raid Zaghal Networking and Media Communications Research Laboratories Department of Computer Science, Kent State University 233 MSB, Kent, OH 44242 javed|qgu@kent.edu Abstract In this paper we present a congestion response mechanism designed for time-sensitive traffic based on the principle of direct protocol interactivity. We envision a transport mechanism, which is interactive and can provide event notification to the subscriber of its communication service. We then show a friendly adaptive MPEG-2 video transcoding scheme, which directly interacts with the transport protocol and adjusts its production with the events in the transport layer. In this paper we present the application side symbiotic mechanics, and report potential dramatic improvement in time-bounded video delivery. Key Words: netcentric applications, TCP interactive, transcoding, MPEG2, temporal QoS. 1. Introduction Congestion is one of the most actively researched areas in networking. However, the mainstream schemes focus on adjusting the delay-bandwidth product of communication and they work fully inside network. Application packets are delayed either in routers or at the network entry-point to cope with occasional congestions. For example, form the point of view of applications a TCP windowing mechanism acts as a network gatekeeper [BrOP94, Jaco88, AlPa99, Tene96]. It eventually performs some form of traffic shaping and introduces time distortion. Such distortion in temporal dimension is considered to be harmless to normal traffic. However, this is not always the case with time sensitive traffic. Indeed, for time sensitive traffic a congestion control scheme based on delaying traffic in many cases may mean a mere shift in the point of packet discard. The situation of a time sensitive application packet in need of transport can be clarified with an analogy to a patient in need of an ambulance. Instead, of being dropped inside the network, in the classical TCP scheme packets are waited at the entry buffer, when the link is congested. A time sensitive packet (such as an audio or video) is often in effect rendered useless at the source. It resembles a situation where the paramedics draw satisfaction from the fact that the patient is not dying in their ambulance, although the packet dies right at the TCP entry buffer waiting for the transport. TCP window buffer spreads a backlog in time. To make the matter worse, the ambulance however returns at some later point in time and picks up the delayed traffic. Effectively this is non usable from application point of view. For time sensitive communication, it not only spells doom for the current data but for packets those follow. Clearly, one of the critical problems in provisioning an integrated solution is that in the current arrangement the applications are not at all being notified of the congestion or of any other network impairment. Rather applications are put to sleep by the network/operating system process. Many of the time sensitive video