Multicast for Savings in Cache-based Video Distribution
Key: GZL+00-1
Author: Carsten Griwodz, Michael Zink, Michael Liepert, Giwon On, Ralf Steinmetz
Date: January 2000
Kind: In proceedings
Publisher: SPIE
Book title: Proceedings of SPIE's Multimedia Computing and Networking Conference 2000 (MMCN'00), San Jose, USA
Abstract: nternet video-on-demand (VoD) today streams videos directly from server to clients, because re-distribution is not established yet. Intranet solutions exist but are typically managed centrally. Caching may overcome these management needs, however existing web caching strategies are not applicable because they work in different conditions. We propose movie distribution by means of caching, and study the feasibility from the service providers' point of view. We introduce the combination of our reliable multicast protocol LCRTP for caching hierarchies combined with our enhancement to the patching technique for bandwidth friendly True VoD, not depending on network resource guarantees. LCRTP is an RFC-conforming extension to the application-level protocol RTP that allows the receivers to allocate exactly the required space for lost data, and supports the retransmission after the initial transfer. However, without additional techniques, this does not save a lot of capacity in real life scenarios. To increase the savings we combine LCRTP with patching. Patching saves server capacity in centralized systems. It works by streaming a video from start to end to the first client that requests this movie. Requests that follow in a limited temporal interval are served by transmitting sufficient information to join the initial stream, and an additional "patch" stream for the missing initial portion of the movie. These subsequent clients use local cyclic buffers to delay play-out of multicast portions of the movie. There is an optimal time before retransmitting a complete movie by multicast, mostly depending on the frequency of requests for a movie. Patching can also be applied recursively to patches. This paper motivates the combined technique and details the elements of an implementation.
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