We propose a Web caching scheme, based on the caching neighborhood protocol, featuring dynamic caching hierarchies as its underlying infrastructure. Dynamic Web caching hierarchies consist of proxy servers building hierarchies on a per request basis, in contrast to static Web caching hierarchies that comprise proxy servers preconfigured into hierarchies. Concerns of overheads and efficiency in forwarding requests individually have driven conventional Web caching schemes to use static Web caching hierarchies. Nevertheless, we show that a Web caching scheme featuring dynamic caching hierarchies can be both efficient and effective in request forwarding.

This paper outlines a generic approach to modeling Web caching schemes. Four Web caching schemes-SH, ICP, CD, and CNP-were modeled to study their performance in terms of request latencies. There were two important findings. First, conventional Web caching schemes such as SH, ICP, and CD would have shorter request latencies if total numbers of levels in their caching hierarchies were one or two. Second, under some reasonable assumptions, CNP was found to outperform the other schemes in terms of request latencies.

In this paper we propose a Caching Neighborhood Protocol (CNP) that describes an infrastructure upon which proxy servers can build dynamic Web caching hierarchies. Such a scheme decreases the response times for the requests by increasing the availability of documents without compromising the currency of the rendered documents. Some qualitative reasonings and studies on the request accessing traces collected by a proxy server at NLANR are presented to justify CNP. A five-day trace analysis shows that the top 20% Web sites (in terms of frequency of accesses) provide 93% of the most frequently accessed top 20% documents and such top 20% documents account for 94% of the documents that have been accessed more than once. Hence, an important observation is that caching the most popular documents provided by the most popular Web sites would be a very effective approach for Web caching.

Code division multiple access (CDMA) has become an attractive technique for media access control in personal communication networks (PCN). Two MAC protocols, namely preamble signaling access (PSA) and minislot signaling access (MSA) are defined and evaluated for voice/data integration at the base station. It assumes that there are two types of mobile hosts, voice mobiles and data mobiles. The base station integrates the data and voice transmission access so that there are no contentions between voice and data users. An adaptive access control is proposed with parameters which affect the system performance. Markovian chain models have been developed to analyze the performance of PSA and MSA protocols. Performance results based upon simulations are also provided.

Two methods recently developed for generating normal deviates within a computer are reviewed along with earlier proposals. A comparison of the various methods for application on an IBM 704 is given. The new direct method gives higher accuracy than previous methods of comparable speed. The detailed inverse technique proposed yields accuracy comparable with, or better than, most previous proposals using about one-quarter the computing time.