A survey of web caching schemes for the Internet <s> I Introduction <s> Prefetching and caching are techniques commonly used in I/O systems to reduce latency. Many researchers have advocated the use of caching and prefetching to reduce latency in the Web. We derive several bounds on the performance improvements seen from these techniques, and then use traces of Web proxy activity taken at Digital Equipment Corporation to quantify these bounds. ::: ::: We found that for these traces, local proxy caching could reduce latency by at best 26%, prefetching could reduce latency by at best 57%, and a combined caching and prefetching proxy could provide at best a 60% latency reduction. Furthermore, we found that how far in advance a prefetching algorithmwas able to prefetch an object was a significant factor in its ability to reduce latency. We note that the latency reduction from caching is significantly limited by the rapid changes of objects in the Web. We conclude that for the workload studied caching offers moderate assistance in reducing latency. Prefetching can offer more than twice the improvement of caching but is still limited in its ability to reduce latency. <s> BIB001 </s> A survey of web caching schemes for the Internet <s> I Introduction <s> Much work in the analysis of proxy caching has focused on high-level metrics such as hit rates, and has approximated actual reference patterns by ignoring exceptional cases such as connection aborts. Several of these low-level details have a strong impact on performance, particularly in heterogeneous bandwidth environments such as modem pools connected to faster networks. Trace-driven simulation of the modem pool of a large ISP suggests that "cookies" dramatically affect the cachability of resources; wasted bandwidth due to aborted connections can more than offset the savings from cached documents; and using a proxy to keep from repeatedly opening new TCP connections can reduce latency more than simply caching data. <s> BIB002
The World Wide Web (WWW) can be considered as a large distributed information system that provides access to shared data objects. The predicted size of the WWW is shown in Figure 1  . As the WWW continues its exponential growth (the size of static Web pages increases approximately 15 % per month), two of the major problems that today's Web users are suffering from are the network congestion and server overloading. The rapid growth of the WWW could be attributed to the fact that at least till now, its usage is quite inexpensive, and accessing information is faster using the WWW than using any other means. Also, the WWW has documents that appeal to a wide range of interests, e.g. news, education, scientific research, sports, entertainment, stock market growth, travel, shopping, weather, maps, etc. Although the Internet backbone capacity increases as 60% per year, the demand for bandwidth is likely to outstrip supply for the foreseeable future as more and more information services are moved onto the Web. If some kind of solution is not undertaken for the problems caused by its rapidly increasing growth, the WWW would become too congested and its entire appeal would eventually be lost. Researchers have been working on how to improve Web performance since the early 90's. Caching popular objects at locations close to the clients has been recognized as one of the effective solutions to alleviate Web service bottlenecks, reduce traffic over the Internet and improve the scalability of the WWW system. The idea of using proxy servers  to cache arose when they were firstly used to allow accesses to the Internet from users within a firewall (see server typically processes requests from within a firewall by forwarding them to the remote servers, intercepting the responses, and sending the replies back to the clients. Since the same proxy servers are typically shared by all clients inside of the firewall, naturally this leads to the question of the effectiveness of using these proxies to cache documents. Clients within the same firewall usually belong to the same organization and likely share common interests. They would probably access the same set of documents and each client tends to browse back and forth within a short period of time. Therefore on the proxy server a previously requested and cached document would likely result in future hits. Web caching at proxy server can not only save network bandwidth but also lower access latency for the clients. shown that caching documents can improve Web performance significantly BIB002 [26] BIB001 . There are several advantages of using Web caching. 1. Web caching reduces bandwidth consumption, thereby decreases network traffic and lessens network congestion.