Architectural considerations for playback of quality adaptive video over the Internet

Lack of QoS support in the Internet has not prevented the rapid growth of streaming applications. However many of these applications do not perform congestion control effectively. Thus there is significant concern about the effects on co-existing well-behaved traffic and the potential for congestion collapse. In addition, the majority of such applications are unable to perform quality adaptation on-the-fly as the available bandwidth changes during a session. This paper provides some architectural insights on the design of video playback applications in the Internet. We present fundamental design principles for Internet applications and identify end-to-end congestion control, quality adaptation and error control as the three major building blocks for Internet video playback applications. We discuss the design space for each of these components, and within that space, present an end-to-end architecture suited for playback of layered-encoded stored video streams. Our architecture reconciles congestion control and quality adaptation which occur on different timescales. It exhibits a TCP-friendly behavior by adopting the RAP protocol for end-to-end congestion control. Additionally it uses a layered framework for quality adaptation with selective retransmission to maximize the quality of the delivered stream as the available bandwidth changes. We argue that the architecture can be generalized by replacing the suggested mechanism for each component by another from the same design space as long as all components remain compatible.