RCache: Design and Analysis of Scalable, Fault Tolerant Multimedia Stream Caching Schemes

In the current Internet, web content is increasingly being cached closer to the end-user to reduce network and web server load and therefore improve performance and user perceived quality. Existing web caching systems1 typically cache entire web documents and attempt to keep them consistent with the origin server. This approach works well for test and images; for bandwidth intensive multimedia data such as audio and video, caching entire documents is not cost effective and does not scale. An alternative approach is to cache parts of the multimedia stream on different caches in the network and coordinate stream playback from these caches. In such a case, the collection of cooperating distributed caches act as a single cache that is both scalable and fault-tolerant. This paper focuses on the design and the evaluation of novel data placement and replacement techniques for such distributed caches. Specifically, we propose schemes that work together: (1) RCache, a family of easy-to-implement, fault-tolerant multimedia data layout schemes that incorporate novel intra- and inter-clip replication controls, (2) TwoD, a two- dimensional local data replacement scheme based on the concept of segment popularity used for data replacement ordering at each cache. Our schemes optimize storage space, start-up latency, server load, network bandwidth usage, and overhead from playback switch-overs. Our simulation results show that the RCache schemes provide 4 - 9 times higher cache hit ratio than a comparable traditional web caching system with the same amount of storage space. Keywords: Web caching, streaming media, distributed caching