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SIGCOMM 1998 LOGO Summary Cache: A Scalable Wide-Area Web Cache Sharing Protocol  
Li Fan, Pei Cao, and Jussara Almeida (University of Wisconsin-Madison) Andrei Z. Broder (Digital Equipment Corporation)  

The sharing of caches among Web proxies is an important technique to reduce Web traffic and alleviate network bottlenecks. Nevertheless it is not widely deployed due to the overhead of existing protocols. In this paper we propose a new protocol called "Summary Cache"; each proxy keeps a summary of the URLs of cached documents of each participating proxy and checks these summaries for potential hits before sending any queries. Two factors contribute to the low overhead: the summaries are updated only periodically, and the summary representations are economical { as low as 8 bits per entry. Using trace-driven simulations and a prototype implementation, we show that compared to the existing Internet Cache Protocol (ICP), Summary Cache reduces the number of inter-cache messages by a factor of 25 to 60, reduces the bandwidth consumption by over 50%, and eliminates between 30% to 95% of the CPU overhead, while at the same time maintaining almost the same hit ratio as ICP. Hence Summary Cache enables cache sharing among a large number of proxies.  
The slides from the presentation are available from the author's site in html, and from the SIGCOMM site in Powerpoint, postscript, and PDF.

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The referenced paper is in Computer Communication Review, a publication of ACM SIGCOMM, volume 28, number 4, October 1998. ISSN # 0146-4833.

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