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With the emergence of various advanced networks that comprise a group of geographically distributed servers, such as content delivery networks (CDNs) and peer-to-peer (P2P) systems, coordinated en-route Web caching in multiserver networks becomes increasingly attractive but remains of great challenge as solutions for single-server networks become invalid here. In this paper, we first establish mathematical formulation for this problem that takes into account all requests (to any server) that pass through the intermediate nodes on a response path and caches the requested object optimally among these nodes so that system's total gain is maximized. Then, we derive efficient dynamic programming-based methods for finding optimal solutions to the problem for the unconstrained case and two QoS-constrained cases, respectively. For each case, we present a caching scheme to illustrate application of the corresponding method. Finally, we evaluate the proposed schemes on different performance metrics through extensive simulation experiments. The experiment results show that our proposed schemes can yield a steady performance improvement and achieve desired QoS in a multiserver network. To the best of our knowledge, these are the first results for solving the problem of coordinated en-route Web caching in multiserver networks.
Date of Publication: May 2009