Cache satellite distribution systems: modeling and analysis

Web caches have become an integral component contributing to the improvement of the performance observed by Web clients. Content Distribution Networks (CDN) and Cache Satellite Distribution Systems (CSDS) have emerged as technologies for feeding the caches with the information clients are expected to request, ahead of time. In a Cache Satellite Distribution System (CSDS), the proxies participating in the CSDS periodically report to a central station about the requests they are receiving from their clients. The central station processes this information and selects a collection of Web documents (or "Web pages"), which it then "pushes" via a satellite broadcast to all, or some, of the participating proxies, hoping most of them will request most documents in the near future. The result is that upon such request, the documents will reside in the local cache, and will not need to be fetched. In this paper we aim at addressing the issues of how to operate the CSDS, how to design it, and how to estimate its effect. Questions of interest are 1) what classes of Web documents should be transmitted by the central station, and how they are characterized, and 2) what is the benefit of adding a particular proxy into a CSDS. We offer a model of this system that accounts for the request streams addressed to the proxies and which captures the intricate interaction between the proxy caches. Unlike models that are based only on the access frequency of the various documents, this model captures both their frequency and their locality of reference. We provide an analysis of this system that is based on the stochastic properties of the traffic streams that can be derived from HTTP logs. The model and analysis can serve as a basis for the design and efficient operation of the system.