Protocol considerations for a prefix-caching proxy for multimedia streams

The increasing popularity of multimedia streaming applications introduces n ew challenges in content distribution. Web-initiated multimedia streams typ ically experience high start-up delay, due to large protocol overheads and the poor delay, throughput, and loss properties of the Internet. Internet s ervice providers can improve performance by caching the initial segment (th e prefix) of popular streams at proxies near the requesting dents. The prox y can initiate transmission to the client while simultaneously requesting t he remainder of the stream from the server. This paper analyzes the challen ges of realizing a prefix-caching service in the context of the IETF's Real -Time Streaming Protocol (RTSP), a multimedia streaming protocol that deriv es from HTTP. We describe how to exploit existing RTSP features, such as th e Range header, and how to avoid several round-trip delays by caching proto col information at the proxy. Based on our experiences, we propose extensio ns to RTSP that would ease the development of new multimedia proxy services . In addition, we discuss how caching the partial contents of multimedia st reams introduces new challenges in cache coherency and feedback control. Th en, we briefly present our preliminary implementation of prefix caching on a Linux-based PC, and describe how the proxy interoperates with the RealNet works server and client. (C) 2000 Published by Elsevier Science B.V. All ri ghts reserved.