Keywords: Cooperative caching system

Cache placement and replacement wn In a the access cost of placing a set of object copies in the routing path. Using this model, the object placement ffective ork tr Summary cache [13] and Cache digests [14]. Che et al. [2] proposed theoretical analysis to anuncooperative two-levelhierarchical cach-ing system where the LRU algorithm is locally run at each cache. Meta algorithms for hierarchical web caching is proposed in [15], however, no cache cooperation was considered in the meta algorithms. Rodriguez et al. illustrated the benefit of cooperative and then the sink will send back the query data. If frequently used data is cached in the intermediate hierarchies from the sink, some queries can be answered by a neighboring caching node instead of fetching from the sink, which will speed up information access in the sensor network. Cooperative caching strategies in wireless net-works have attracted widely attention in the recent years due to this significant advantage [21,10,22–24,8,25,26]. In this paper, we address an important issue in cooperative caching systems: online cache decision to improve system effi-ciency. Given a set of caches, their network distances and access frequencies, the problem is to decide which objects should b