|Title:||Peer-to-peer cooperative caching in mobile environments|
|Subject:||Hong Kong Polytechnic University -- Dissertations|
Wireless communication systems
|Department:||Department of Computing|
|Pages:||xi, 183 leaves : ill. ; 30 cm|
|Abstract:||Caching is a key technique for improving the data retrieval performance of mobile clients, who will store frequently needed data items in their local cache, often of a limited size. The emergence of the state-of-the-art peer-to-peer communication technologies now brings to reality what we call "cooperative caching" in which mobile clients can help one another in caching. They not only can retrieve data items from mobile support stations, but also from the cache in their peers, realizing a new dimension for mobile data caching. This thesis proposes a COoperative CAching scheme, called COCA, which can be tailored for pull-based, push-based and hybrid mobile environments. COCA was found to improve the access latency of client requests and the amount of relatively expensive requests forwarded to the server in the pull-based environment. It can also effectively reduce power consumption in the push-based and hybrid environments. We propose a cache signature scheme for the mobile clients to provide hints for them to determine whether to search the cache of their peers or directly enlist the server for help. We observe the need for cooperating peers to cache useful data items together, so as to further improve cache hit from peers. This could be realized by capturing the data requirement of individual peers in conjunction with their mobility patterns, for which we respond with two group-based cooperative caching schemes for mobile clients: centralized and distributed group-based COCA schemes or CGCoca and DGCoca respectively. We define a tightly-coupled group (TCG) as a collection of peers that possess similar mobility pattern and display similar data affinity. Built upon the COCA system, we propose a family of centralized and distributed algorithms to discover and maintain all TCGs dynamically in CGCoca and DGCoca respectively. Two cooperative cache management protocols: cooperative cache admission control and cooperative cache replacement, are proposed to improve data accessibility in TCGs. We conduct performance studies of our COCA schemes based upon simulated experiments. The group-based COCA schemes are shown to outperform the conventional caching scheme, standard COCA and COCA with cache signature scheme. In the group-based COCA schemes, DGCoca is also found to perform better than CGCoca, as DGCoca is more effective in discovering and maintaining TCGs in mobile environments.|
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