In this paper we study content retrieval delay in a hybrid content distribution system, e.g., emerging content cloud [1], where a requested content item can be vertically retrieved from the central server and horizontally retrieved from network nodes. The content retrieval delay depends on the load intensities of the retrieval sources, which have asymmetric system properties such as bandwidth and cache capacity. The retrieval traffic is generated due to heterogeneous content availability, i.e., content diffusion resulting from the applied caching policies, and the selection of retrieval sources. To optimize the retrieval delay, the advantages of the network nodes should be utilized while also leveraging the caching and retrieval capacity of the server. We present analytical models to evaluate the content retrieval delay under two retrieval selection strategies, i.e., Bernoulli and Shortest-Queue, and three caching policies: selfish, altruistic, and our proposed hybrid caching policy which partitions the content items into three categories, each employing different caching schemes. The traffic loads and latency of a given combination of source selection and caching policy are derived based on the content diffusion and distribution in the entire system. The simulation and analytical results show that a satisfactory content retrieval delay is achieved when the retrieval selection is load-aware and the caching policies can effectively utilize the cache storage and retrieval capacity of both the network nodes and the server. In particular, the proposed hybrid caching policy combined with Shortest-Queue selection is shown to scale with various network configuration and to adapt to
the load changes in our experiment results.
[1] http://aws.amazon.com/cloudfront/.
A shorter version of this paper has appeared in: Proc. 2010 IEEE Int'l Symp. on Modeling, Analysis & Simulation of Computer and Telecommunication Systems "MASCOTS 2010," Miami, FL (IEEE, August 2010) 397 - 399 .
By: Mathias Bjoerkqvist, Lydia Y. Chen
Published in: RZ3781 in 2010
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