On multiple description streaming with content delivery networks

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Abstract
CDNs have been widely used to provide low latency, scala- bility, fault tolerance, and load balancing for the delivery of web content and more recently streaming media. We propose a system that improves the performance of streaming media CDNs by exploiting the path diver- sity provided by existing CDN infrastructure. Path diversity is provided by the different network paths that exist between a client and its nearby edge servers; and multiple description (MD) coding is coupled with this path di- versity to provide resilience to losses. In our system, MD coding is used to code a media stream into multiple complementary descriptions, which are distributed across the edge servers in the CDN. When a client requests a media stream, it is directed to multiple nearby servers which host comple- mentary descriptions. These servers simultaneously stream these comple- mentary descriptions to the client over different network paths. This paper provides distortion models for MDC video and conventional video. We use these models to select the optimal pair of servers with com- plementary descriptions for each client while accounting for path lengths and path jointness and disjointness. We also use these models to evaluate the performance of MD streaming over CDNs in a number of real and gen- erated network topologies. Our results show that distortion reduction by about 20 to 40% can be realized even when the underlying CDN is not de- signed with MDC streaming in mind. Also, for certain topologies, MDC requires about 50% fewer CDN servers than conventional streaming tech- niques to achieve the same distortion at the clients.

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