In this paper, we investigate the object placement problem in distributed cooperative proxy systems and build a mathematics model. We prove that the problem is a NP-Hard problem and two novel greedy heuristic placement algorithms MWLC and MWGB are proposed to get the near-optimal answer in a polynomial complexity. We perform simulation and the results reported in this paper show that these two algorithms could achieve better performance than the traditional MFU algorithm (about 13.05% and 14.13% respectively). By the analysis of the experiment results, we find that the two algorithms can efficiently reduce the average request cost and balance the load of proxies. In general, the technologies proposed in this paper could be used to develop effective distributed cooperative proxy systems such as CDSP and digital library and so on.
With the dramatic growth of multimedia streams, the efficient distribution of stored videos has become a major concern. There are two basic caching strategies: the whole caching strategy and the caching strategy based on layered encoded video, the latter can satisfy the requirement of the highly heterogeneous access to the Internet. Conventional caching strategies assign each object a cache gain by calculating popularity or density popularity, and determine which videos and which layers should be cached. In this paper, we first investigate the delivery model of stored video based on proxy, and propose two novel caching algorithms, DPLayer (for layered encoded caching scheme) and DPWhole (for whole caching scheme) for multimedia proxy caching. The two algorithms are based on the resource allocation model of dynamic programming to select the optimal subset of objects to be cached in proxy. Simulation proved that our algorithms achieve better performance than other existing schemes. We also analyze the computational complexity and space complexity of the algorithms, and introduce a regulative parameter to compress the states space of the dynamic programming problem and reduce the complexity of algorithms.