Delimiting the range of effectiveness of scalable on-demand streaming

  • Authors:

  • Haonan Tan;Derek L. Eager;Mary K. Vernon

  • Affiliations:

  • Computer Sciences Department, University of Wisconsin, Madison, WI;Department of Computer Science, University of Saskatchewan, Saskatchewan, Canada;Computer Sciences Department, University of Wisconsin, Madison, WI

  • Venue:
  • Performance Evaluation
  • Year:
  • 2002

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Abstract

Previous analyses of scalable streaming protocols for delivery of stored multimedia have largely focused on how the server bandwidth required for full-file delivery scales as the client request rate increases or as the start-up delay is decreased. This previous work leaves unanswered three questions that can substantively impact the desirability of using these protocols in some application domains, namely: (1) Are simpler scalable download protocols preferable to scalable streaming protocols in contexts where substantial start-up delays can be tolerated? (2) If client requests are for (perhaps arbitrary) intervals of the media file rather than the full-file, are there conditions under which streaming is not scalable (i.e., no streaming protocol can achieve sub-linear scaling of required server bandwidth with request rate)? (3) For systems delivering a large collection of objects with a heavy-tailed distribution of file popularity, can scalable streaming substantially reduce the total server bandwidth requirement, or will this requirement be largely dominated by the required bandwidth for relatively cold objects?This paper addresses these questions primarily through the development of tight lower bounds on required server bandwidth, under the assumption of Poisson, independent client requests. Implications for other arrival processes are also discussed. Previous work and results presented in this paper suggest that these bounds can be approached by implementable policies. With respect to the first question, the results show that scalable streaming protocols require significantly lower server bandwidth in comparison to download protocols for start-up delays up to a large fraction of the media playback duration. For the second question, we find that in the worst-case interval access model, the minimum required server bandwidth, assuming immediate service to each client, scales as the square root of the request rate. Finally, for the third question, we show that scalable streaming can provide a factor of log K improvement in the total minimum required server bandwidth for immediate service, as the number of objects K is scaled, for systems with fixed minimum object request popularity.