Hierarchical image caching in content distribution networks

The efficient distribution of stored information has become a major concern in the Internet. Since the Web workload characteristics shows that more than 60 % of network traffic is caused by image documents, how to efficiently distribute image documents from servers to end clients is an important issue. The proxy cache is an efficient solution to reduce network traffic. It has been shown that an image caching method (graceful caching) based on a hierarchical coding format showed better performance than conventional caching schemes. However, as the capacity of the cache is limited, how to efficiently allocate the cache memory to achieve a minimum expected delay time is still a problem to be resolved. This paper presents an integrated caching algorithm to deal with the above problem in the Internet. By analyzing the Web request distribution of graceful caching, both replacement and pre-fetching algorithms are proposed. We also show that our proposal can be carried out based on information readily available in the proxy server and it flexibly adapts its parameters to the hit rates and access pattern of users' requesting documents in the graceful caching. We finally verify the performance of this algorithm by simulations.