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

Packet level discrete event network simulators use an event to model the movement of each packet in the network. This results in accurate models, but requires that many events are executed to simulate large, high bandwidth networks. Fluid-based network simulators abstract the model to consider only changes in rates of traffic flows. This can result in large performance advantages, though information about the individual packets is lost making this approach inappropriate for many simulation and emulation studies. We present a hybrid model in which packet flows and fluid flows coexist and interact. This enables studies to be performed with background traffic modelled using fluid flows and foreground traffic modelled at the packet level. Results presented show up to 20 times speedup using this technique. Accuracy is within 4% for latency and 15% for jitter in many cases.

/pdf/hybrid-packet-fluid-flow-network-simulation-3y1wohuay3.pdf

Hybrid packet/fluid flow network simulation

The demand for cellular data networks is expected to increase with 3G and beyond technologies accompanied by high-bandwidth consumer services, such as wireless video and camera phones. User mobility affects quality of service, and makes capacity planning more difficult. This paper presents an analysis of user mobility patterns based on data traffic traces from a major regional CDMA2000 cellular network. We find low overall mobility in the network, power-law characteristics in user mobility profiles, and weak correlations between call activity and mobility levels for individual users. We also find that users concentrate their activity in a "home cell" with frequent shorter trips to other locations in the network. Based on the empirical findings, we develop and parameterize a model of cellular data user mobility and show its practical use in simulation.

http://pages.cpsc.ucalgary.ca/~carey/papers/2005/pewasun2005.pdf

Characterizing and modeling user mobility in a cellular data network

The TCP protocol often suffers from performance problems in conventional single-channel multihop wireless ad hoc networks. The problems arise from hidden node and exposed node issues, which can lead to channel contention in the forward direction between TCP DATA packets that are part of the same TCP flow control window, as well as contention between TCP DATA and TCP ACK packets flowing in opposite directions. In this paper, we propose and evaluate a novel bidirectional multi-channel MAC protocol designed to improve TCP performance over a multihop wireless network. The protocol uses multiple transmission channels at the physical layer to reduce TCP DATA-DATA contention, and bidirectional RTS/CTS channel reservations to reduce TCP DATA-ACK collisions. With four channels, simulation results for static multihop networks show TCP throughput gains of 50% to 180%, compared to a conventional IEEE 802.11 MAC protocol. Fairness is also improved with our protocol, since contention is confined to a short handshake period on the control channel.

A bidirectional multi-channel MAC protocol for improving TCP performance on multihop wireless ad hoc networks

Communication systems are undergoing a change in use from stream to request-response or transaction communication In addition, communication systems are becoming increasingly based on high-speed, low delay, low error rate channels These changes call for a new generation of networks, network interfaces, and transport protocol design The performance characteristics of request-response protocols on these high-performance networks should guide the design of this new generation, yet relatively little data of this nature is availableIn this paper, we present some preliminary measurements of network traffic for a cluster of workstations connected by Ethernet running the V distributed operating system We claim that this system, with its use of a high-speed local area network and a request-response transport protocol tuned for RPC, provides some indication of the performance characteristics for systems in the next generation of communication systems In particular, these measurements provide an indication of network traffic patterns, usage characteristics for request-response protocols, and the behavior of the request-response protocol itself These measurements suggest in general that a key design focus must be on minimizing network latency and that a request-response protocol is well-suited for this goal This focus has implications for protocol design and implementation as well as for the design of networks and network interfaces

Network measurement of the VMTP request-response protocol in the V distributed system

This article presents an overview of the most significant changes in wireless data traffic and its main driving forces throughout the past decade (1998-2008). The main axes of change are discussed: wireless technology, user population, and applications. Evolution of wireless technology realized a 200-fold increase in data rate, and facilitated a continuous enrichment of the traffic mix traversing legacy and modern wireless networks. New applications emerged, such as peer-to-peer file sharing, online gaming, and multimedia, establishing a trend of significant increase in traffic volume. User population has also increased and even saturated some markets. However, not all benefits of wireless technologies are equally exploited, with only a few users exercising high mobility or regularly enjoying multimedia services. Future indications include a requirement for either integration or interoperability of two mainstream wireless technologies, WiFi and cellular, as well as continuous user demand for more bandwidth, broader coverage, and better mobility support.

Carey Williamson

Papers

Hybrid packet/fluid flow network simulation

Characterizing and modeling user mobility in a cellular data network

A bidirectional multi-channel MAC protocol for improving TCP performance on multihop wireless ad hoc networks

Network measurement of the VMTP request-response protocol in the V distributed system

Wireless data traffic: a decade of change