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Unformatted text preview: 1 PAPER Special Issue on Internet Technology Streaming Video over TCP with Receiver-based Delay Control Pai-Hsiang HSIAO , H.T. KUNG , and Koan-Sin TAN , Nonmembers SUMMARY Unicasting video streams over TCP connections is a chal- lenging problem, because video sources cannot normally adapt to delay and throughput variations of TCP connections. This paper describes a method of extending TCP so that TCP connections can effectively carry hierarchically-encoded layered video streams, while being friendly to other competing connections. We call the method Receiver-based Delay Control (RDC). Under RDC, a TCP connection can slow down its transmission rate to avoid congestion by delaying ACK packet generation at the TCP receiver based on congestion notifications from routers. We present the principle be- hind RDC, argue that it is TCP-friendly, describe an implementation that uses 1-bit congestion notification from routers, and demonstrate by simu- lations its effectiveness in streaming hierarchically-encoded layered video. key words: video streaming, layered video, TCP, retransmission timeout, delay control 1. Introduction TCP is a dominant transport layer protocol in current Inter- net. It would be desirable if video and audio streams could be carried over TCP connections to take advantage of TCPs congestion control capabilities. However, it is well recog- nized that current TCP implementations are not suited for this purpose because TCP connections could introduce sig- nificant delay and throughput variations in the delivery of data . There have been many proposals on new transport pro- tocols for the purpose of solving this video transport prob- lem, see e.g. the work by Rejaie et. al . These protocols need to be TCP-friendly to ensure that they will not cause network collapse . However, proving a new trans- port protocol to be TCP-friendly can be difficult, because the dynamics of TCP congestion control is extremely complex . In this paper, we take a different approach: we extend TCP to make it suitable for transporting video, without mod- ifying the TCP congestion control algorithm. In particular, we do not change the TCP sender code that governs TCPs behavior in the slow-start and congestion avoidance phases. The only change we make is on the TCP receiver side. In fact, our change is no more than extending the delayed ACK feature  in current TCP implementations, so that a longer delay can be imposed on ACKing (sending of ACK packets for received data packets) to avoid network congestion. For these reasons, we believe that our approach is, by design, TCP-friendly. We call this method Receiver-based Delay Division of Engineering and Applied Sciences, Harvard Uni- versity, USA Institute of Information Management, National Chiao-Tung University, Taiwan Control (RDC)....
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- Fall '08