We will review some of the major results in random graphs and some of the more challenging open problems. We will cover algorithmic and structural questions. We will touch on newer models, including those related to the WWW.

Random graphs

Established in 2006, TATA Africa Services (Nigeria) Limited operates as the nodal point for Tata businesses in West Africa. TATA Africa Services (Nigeria) Limited has a strong presence in Nigeria with investments exceeding USD 10 million. The company was established in Lagos, Nigeria as a subsidiary of TATA Africa Holdings (SA) (Pty) Limited, South Africa and serves as the hub of Tata’s operations in Nigeria and the rest of West Africa.

What About Us

It is shown that, particularly for terrestrial cellular telephony, the interference-suppression feature of CDMA (code division multiple access) can result in a many-fold increase in capacity over analog and even over competing digital techniques. A single-cell system, such as a hubbed satellite network, is addressed, and the basic expression for capacity is developed. The corresponding expressions for a multiple-cell system are derived. and the distribution on the number of users supportable per cell is determined. It is concluded that properly augmented and power-controlled multiple-cell CDMA promises a quantum increase in current cellular capacity. >

On the capacity of a cellular CDMA system

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 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.

/pdf/self-similarity-in-world-wide-web-traffic-evidence-and-4olkshqr0k.pdf

Self-similarity in World Wide Web traffic: evidence and possible causes

Web usage mining is the application of data mining techniques to discover usage patterns from Web data, in order to understand and better serve the needs of Web-based applications. Web usage mining consists of three phases, namely preprocessing, pattern discovery, and pattern analysis. This paper describes each of these phases in detail. Given its application potential, Web usage mining has seen a rapid increase in interest, from both the research and practice communities. This paper provides a detailed taxonomy of the work in this area, including research efforts as well as commercial offerings. An up-to-date survey of the existing work is also provided. Finally, a brief overview of the WebSIFT system as an example of a prototypical Web usage mining system is given.

/pdf/web-usage-mining-discovery-and-applications-of-usage-4qn3qjomy4.pdf

Web usage mining: discovery and applications of usage patterns from Web data

Today, many Web sites dynamically generate responses "on the fly" when user requests are received. In this paper, we experimentally evaluate the impact of three different dynamic content technologies (Perl, PHP, and Java) on Web server performance. We quantify achievable performance first for static content serving, and then for dynamic content generation, considering cases both with and without database access. The results show that the overheads of dynamic content generation reduce the peak request rate supported by a Web server up to a factor of 8, depending on the workload characteristics and the technologies used. In general, our results show that Java server technologies typically outperform both Perl and PHP for dynamic content generation, though performance under overload conditions can be erratic for some implementations.

/pdf/a-performance-comparison-of-dynamic-web-technologies-4zc7zc3h4q.pdf

A performance comparison of dynamic Web technologies

Two classic categories of models exist for computer networks: network information flow and network of queues. The network information flow model appropriately captures the multi-hop flow routing nature in general network topologies, as well as encodable and replicable properties of information flows. However, it assumes nodes in the network to be infinitely powerful and therefore does not accurately model queueing delay and loss at nodes. The network of queues model instead focuses on finite capacitied nodes and studies buffering and loss behaviors from a stochastic perspective. However, existing models on network of queues are mostly based on unrealistically simple topologies, and lacks the multi-hop flow routing dimension. In this work, we seek to combine advantages from both models. We start with the network information flow model and replace each infinitely powerful node with afinitely capacitied queue system instead. We show that the optimal routing problems for unicast, multiple unicasts and multicast can all be formulated as convex optimization problems. As a necessary step in validating the model for multicast routing, we show that network coding does not change the memoryless nature of traffic. We examine the correctness of the models through simulations and show that they behave differently than traditional link-cost based network flow models.

Network Information Flow in Network of Queues

Loss-load curves: support for rate-based congestion control in high-speed datagram networks

Mosaic traac (i.e., WorldWide Web) is the fastest growing component of the aggregate packet and byte traac on the NSFNET backbone. Modeling the work-load characteristics of these mosaic sessions is therefore deemed important in any simulation study of the Inter-net or future high speed networks. The ATM-TN TeleSim project has designed and implemented a synthetic workload model for Internet mosaic traac, to be used as input to a parallel simulator for high speed ATM networks. This paper describes the workload characterization and modeling process for this synthetic workload model, as well as the design, implementation , and validation of this traac model.

A Synthetic Workload Model for Internet Mosaic Traffic

The paper describes an interactive graphical user interface (GUI) that can be used for the modeling and analysis of Web proxy workloads. The WebTraff GUI has three main components. First, the WebTraff tool provides a visual front-end to ProWGen, a Web proxy workload generation tool developed in prior work (see Busari, M. and Williamson, C., Computer Networks, vol.38, no.6, p.779-94, 2002), which can be used for generating synthetic Web proxy workloads of arbitrary length, with user-specified statistical properties. Second, the WebTraff GUI provides tools for the analysis of Web proxy workload characteristics, including document size distribution, document popularity profile, and temporal locality properties. Third, the GUI provides a front-end to a simple Web proxy cache simulation program, which can be used in studies of Web proxy cache performance and cache filter effects.

/pdf/webtraff-a-gui-for-web-proxy-cache-workload-modeling-and-3h5hv2f6cn.pdf

Carey Williamson

Papers

A performance comparison of dynamic Web technologies

Network Information Flow in Network of Queues

Loss-load curves: support for rate-based congestion control in high-speed datagram networks

A Synthetic Workload Model for Internet Mosaic Traffic

WebTraff: a GUI for Web proxy cache workload modeling and analysis