MUMOC Prefix Caching

The content cache module offers functions for online VoD caching and dynamic merging of VoD prefixes and whole presentations and enforces cache replacement strategies at any node.


The caching-enabled proxy is the content cache core. MUMOC dynamically deploys it; there is one caching-enabled proxy for each served VoD flow to achieve per-flow adaptation and tailoring. The caching-enabled proxy exploits three main components, as shown in Figure 1: cache manager, list manager, and cache writer. In addition, the Proxy Agent, implements the necessary signaling to communicate with other distributed components along the activated client-server path, e.g., during prefix/full-presentation merging.



Figure 1: The MUMOC Metadata Browser





When a caching-enabled Proxy Agent decides to cache a traversing VoD flow, it gets a cache writer from the cache manager and exploits it to save the stream to a temporary file. MUMOC performs onlineVoD caching, i.e., it intercepts the stream delivered to the client and caches it along the service path without producing additional bandwidth consumption.

Prefix/full-presentation merging occurs when a client requests a VoD flow whose prefix (but not the whole flow) is currently cached. In this case, to reduce the delay time for playback startup at the requesting client, MUMOC immediately begins prefix streaming, and then queries the metadata browser to find a suitable VoD server storing the requested whole video, by asking to start the transmission from the VoD frames that follow the cached prefix. When MUMOC terminates prefix streaming, the active middleware automatically switches to the traversing video flow and goes on with VoD delivery.

To achieve high flexibility and dynamicity, MUMOC permits to apply different replacement strategies to each store, and to change strategy also at runtime. This is possible because the list manager dynamically considers the locally installed replacement policies.

References

  • P. Bellavista, A. Corradi, L. Foschini, "MUMOC: an Active Infrastructure for Open Video Caching", Proceedings of the 1st International Conference on Distributed Frameworks for Multimedia Applications (DFMA'05), Besançon, France, February 6-9, 2005, IEEE Computer Society Press.

 


 
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on May 2005
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