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Caching improves the performance of Web servers by placing frequently accessed data at intermediate nodes close to Web clients. Similarly, in a mobile network, access delay can be reduced by caching data objects near the mobile clients. Existing caching techniques used for Web servers are unsuitable for mobile networks because they do not deal with the issue of client mobility. To ensure cache performance is not affected by client movement, object relocation techniques can be used to dynamically relocate data objects so they remain close to the moving client. Existing relocation techniques rely on path predictions to help make relocation decisions. However, the inaccuracy of path prediction techniques result in high relocation overhead and increased access delay after each handover. In this paper, we propose two new object relocation techniques to deal with the problem of poor path predictions and high object relocation overhead. The first technique called 2PR (two-phase relocation) compensates for the inaccuracy of existing path prediction algorithms by temporarily relocating data objects to a common parent node until the client's location is confirmed. The second technique, called ROLP (return-path object-list passing), reduces the traffic overhead associated with object relocation by using coordination messages between nodes. Test results show that 2PR and ROLP reduce the penalty of poor path predictions and significantly reduces the overhead associated with cache relocation compared to existing schemes.
Date of Conference: 7-9 July 2004