Content Retrieval Delay Driven by Caching Policy and Source Selection

In this paper we study the content retrieval delay in a hybrid content distribution system, e.g., emerging content clouds [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 arises 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. The traffic loads and latency of a given combination of source selection and caching policy is derived based on the content diffusion and distribution in the entire system. The simulation and analytical results show that 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.