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.

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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

In this paper, we study the dynamics of coupled speed scaling systems, in which service rate is a function of system occupancy. We focus on both Processor Sharing (PS) and Shortest Remaining Processing Time (SRPT) as scheduling disciplines, and study their speed scaling dynamics under heavy load. Using a combination of Markov chain analysis and discrete-event simulation, we identify several important properties of speed scaling systems, which we call the autoscaling effect, the alpha effect, and the saturation effect. We also identify different overload regimes for PS and SRPT. In particular, SRPT exhibits a starvation effect that differs from the compensation effect of PS. These dynamics lead todifferent stability, fairness, and robustness properties for PS and SRPT under heavy load.

Autoscaling Effects in Speed Scaling Systems

Impacts of data call characteristics on multi-service CDMA system capacity

Analyzing traces of wireless network activity has many pragmatic purposes, from capacity planning to network design. Unfortunately, capturing complete traces of wireless traffic is difficult, and using incomplete traces can degrade the quality of the aforementioned analyses. In this paper we examine three different methods for estimating the completeness of wireless traces. We find that a method that examines MAC-layer sequence numbers provides the most accurate results. We also examine the effect of the placement of wireless sensors on the completeness of wireless-side traces. We determine that locating sensors such that the signal strengths between clients and access points is over 40% results in low miss rates at the sensor, and few CRC errors.

https://pages.cpsc.ucalgary.ca/~carey/papers/2007/aniket-wowmom2007.pdf

Assessing the Completeness of Wireless-side Tracing Mechanisms

Mobility models play an important role in the evaluation of wireless ad hoc networks. However, most existing mobility models are limited to 1D or 2D user movement. In this paper, we propose a novel 2.5D mobility model suitable for modeling the movement of backcountry skiers in mountainous terrains. These skiers carry wireless devices for communication in the event of emergencies, such as an avalanche, and thus form a dynamic mobile wireless ad hoc network. Our model represents groups of skiers, with each group having an invisible leader who determines the general direction of movement. We calculate the acceleration, velocity, and position of the group leader based on properties of the terrain, gravitational force, and a randomized sine function. To simulate the coordinated mobility of group members, we use a flocking model, which applies cohesion, separation, and alignment forces to influence group members to follow their leader, while avoiding collisions with each other. To demonstrate the applicability of our model, we use simulation to evaluate the skier rescue probability in the event of an avalanche.

/pdf/physics-based-modeling-of-skier-mobility-and-avalanche-2173zyogah.pdf

Physics-based modeling of skier mobility and avalanche rescue in mountainous terrain

Quality of Service (QoS) can be provided in a Wireless Local Area Network (WLAN) using the Enhanced Distributed Channel Access (EDCA) mechanism specified in IEEE 802.11e. However, 802.11e WLANs are not widely deployed and not all WLAN vendors implement the 802.11e mechanisms. In this paper, we propose and evaluate an asymmetric QoS solution, in which QoS support is provided only at the wireless Access Point (AP). We believe that this approach provides a practical solution for many cases where wireless clients may not support EDCA QoS. The feasibility of this solution is studied, using an experimental approach. A QoS testbed is designed and implemented using a centralized wireless controller and lightweight AP. The measurement results show that VLAN-based asymmetric QoS provides effective prioritization and excellent performance for high-priority traffic classes, including Voice over IP (VoIP) and TCP traffic, even during severe congestion conditions. Furthermore, this approach can be easily implemented using minimal equipment.

/pdf/experimental-evaluation-of-asymmetric-qos-in-ieee-802-11g-2ikif7mlzl.pdf

Carey Williamson

Papers

Autoscaling Effects in Speed Scaling Systems

Impacts of data call characteristics on multi-service CDMA system capacity

Assessing the Completeness of Wireless-side Tracing Mechanisms

Physics-based modeling of skier mobility and avalanche rescue in mountainous terrain

Experimental evaluation of asymmetric QoS in IEEE 802.11g wireless networks