Recently the notion of self-similarity has been shown to apply to wide-area and local-area network traffic. In this paper we examine the mechanisms that give rise to the self-similarity of network traffic. We present a hypothesized explanation for the possible self-similarity of traffic by using a particular subset of wide area traffic: traffic due to the World Wide Web (WWW). Using an extensive set of traces of actual user executions of NCSA Mosaic, reflecting over half a million requests for WWW documents, we examine the dependence structure of WWW traffic. While our measurements are not conclusive, we show evidence that WWW traffic exhibits behavior that is consistent with self-similar traffic models. Then we show that the self-similarity insuch traffic can be explained based on the underlying distributions of WWW document sizes, the effects of caching and user preference in le transfer, the effect of user "think time", and the superimposition of many such transfers in a local area network. To do this we rely on empirically measured distributions both from our traces and from data independently collected at over thirty WWW sites.

The growing popularity of the World Wide Web is placing tremendous demands on the Internet. A key strategy for scaling the Internet to meet these increasing demands is to cache data near clients and thus improve access latency and reduce network and server load. Unfortunately, research in this area has been hampered by a poor understanding of the locality and sharing characteristics of Web-client accesses. The recent popularity of Web proxy servers provides a unique opportunity to improve this understanding, because a small number of proxy servers see accesses from thousands of clients. This paper presents an analysis of access traces collected from seven proxy servers deployed in various locations throughout the Internet. The traces record a total of 47.4 million requests made by 23,700 clients over a twenty-one day period. We use a combination of static analysis and trace-driven cache simulation to characterize the locality and sharing properties of these accesses. Our analysis shows...

Recently the notion of self-similarity has been shown to apply to wide-area and local-area network traffic. In this paper we examine the mechanisms that give rise to self-similar network traffic. We present an explanation for traffic self-similarity by using a particular subset of wide area traffic: traffic due to the World Wide Web (WWW). Using an extensive set of traces of actual user executions of NCSA Mosaic, reflecting over half a million requests for WWW documents, we show evidence that WWW traffic is selfsimilar. Then we show that the self-similarity in such traffic can be explained based on the underlying distributions of WWW document sizes, the effects of caching and user preference in file transfer, the effect of user "think time", and the superimposition of many such transfers in a local area network. To do this we rely on empirically measured distributions both from our traces and from data independently collected at over thirty WWW sites. 1 Introduction Understanding the ...

With the increasing demand for document transfer services such as the World Wide Web comes a need forbetter resource management to reduce the latency of documents in these systems. To address this need, we analyze the potential for document caching at the application level in document transfer services. We have collected traces of actual executions of Mosaic, re ecting over half a million user requests for WWW documents. Using those traces, we study the tradeo s between caching at three levels in the system, and the potential for use of application-level information in the caching system. Our traces show that while a high hit rate in terms of URLs is achievable, a much lower hit rate is possible in terms of bytes, because most pro tably-cached documents are small. We consider the performance ofcaching when applied at the level of individual user sessions, at the level of individual hosts, and at the level of a collection of hosts on a single LAN. We show that the performance gain achievable by caching at the session level (which is straightforward to implement) is nearly all of that achievable at the LAN level (where caching is more di cult to implement). However, when resource requirements are considered, LAN level caching becomes much more desirable, since itcan achieve a given level of caching performance using a much smaller amount of cache space. Finally, we consider the use of organizational boundary information as an example of the potential for use of application-level information in caching. Our results suggest that distinguishing between documents produced locally and those produced remotely can provide useful leverage in designing caching policies, because of di erences in the potential for sharing these two document types among multiple users. 1

The continued increase in demand for information services on the Internet is showing signs of strain. While the Internet is a highly distributed system, individual data objects most often have only a single source. Host computers and network links can easily become overloaded when a large number of users access very popular data. Proxy-caching is currently a popular way to reduce network bandwidth, server load and to improve response time to the user. The original caching proxy, from CERN, is probably still the most widely used. This paper describes software developed by the author that investigates some alternative techniques for caching World-Wide Web objects. This software complements traditional proxycaching by allowing servers to explicitly grant or deny permission to cache an object, and with support for server-initiated callback invalidation of changed objects. 1 Introduction Statistics collected on the NSFNET backbone were indicating that World-Wide Web traffic would exceed th...

ManyWorld-Wide Web clients today are connected to the Internet via low-speed computer links. Examples are home users accessing the Internet through telephone lines, and wireless computer users. This form of communication is characterized by a client being attached to a high-bandwidth network through a poor link. This thesis examines techniques that can help bring Web performance for such poorlyconnected clients more in line with others that are well-connected. A prefetching scheme that is realized at a proxy server one network hop away from the clientis proposed. The client does not need to be aware that prefetching is being performed# it is only aware of a perceived reduction in latency. The prefetching scheme considered takes full advantage of characteristics unique to the World-Wide Web, and it adapts dynamically to changing user behavior. A wireless network is emulated and used to help validate the ideas presented.

World Wide Web services are continuing to grow along with the number of clients connecting to the Internet and the transfer rates of their connections. News is one of the main areas of usage of clients today. It is also an area which has not received much attention from the research community. In this thesis, we investigate several aspects of news on demand (NoD) services on the Internet today. We analyze log files of a news server and a streaming server from Norway's largest online newspaper Verdens Gang (VG). Our focus is on the content in a NoD environment, users behavior with the content, and object popularity in terms of both news articles and streaming objects. The most central topics we investigate are types of files on these servers, size distribution, access and interaction patterns, object lifetime, and if the Zipf popularity distribution applies in this scenario.

In this paper we survey the field of Algorithmic Foundations of the Internet, which is a new area within theoretical computer science. We consider six sample topics that illustrate the techniques and challenges in this field. 1

Recent developments in office productivity suites make it easier for users to publish rich compound documents on the Web. Compound documents appear as a single unit of information but may contain data generated by different applications, such as text, images, and spreadsheets. Given the popularity enjoyed by these office suites and the pervasiveness of the Web as a publication medium, we expect that in the near future these compound documents will become an increasing proportion of the Web's content. As a result, the content handled by servers, proxies, and browsers may change considerably from what is currently observed. Furthermore, these compound documents are currently treated as opaque byte streams, but future Web infrastructure may wish to understand their internal structure to provide higher-quality service.