The world of computers experienced an explosive period of growth toward the end of the 20th century with the widespread availability of the Internet and the development of the World Wide Web. As people began using computer networks for everything from research and communication to banking and commerce, network failures became a greater concern because of the potential to interrupt critical applications. Fault tolerance systems were developed to detect and correct network failures within minutes and eventually within seconds of the failure, but time-critical applications such as military communications, video conferencing, and Web-based sales require better response time than any previous systems could provide. The goal of this thesis was the development and implementation of a Network Fault Tolerance (NFT) system that can detect and recover from failures of network interface cards, network cables, switches, and routers in much less than one second from the time of failure. The problem was divided into two parts: fault tolerance within a single local area network (LAN), and fault tolerance across many local area networks. The first part involves the network interface cards, network cables, and switches within a LAN, which the second part involves the routers that connect LANs into larger internetworks. Both parts of the NFT solution were implemented on Windows NT 4.0 PC's connected by a switched Fast Ethernet network. The NFT system was found to correct system failures within 300 milliseconds of the failure.

"Real-time performance evaluation of wireless local area networks (WLANs) is an extremely challenging topic. The major drawback of real-time performance analysis in actual network installations is a lack of repeatability due to uncontrollable interference and propagation complexities. These are caused by unpredictable variations in the interference scenarios and statistical behavior of the wireless propagation channel. This underscores the need for a Radio Frequency (RF) test platform that provides isolation from interfering sources while simulating a real-time wireless channel, thereby creating a realistic and controllable radio propagation test environment. Such an RF-isolated testbed is necessary to enable an empirical yet repeatable evaluation of the effects of the wireless channel on WLAN performance. In this thesis, a testbed is developed that enables real-time laboratory performance evaluation of WLANs. This testbed utilizes an RF-isolated test system, Azimuthâ„¢ Systems 801W, for isolation from external interfering sources such as cordless phones and microwave ovens and a real-time multipath channel simulator, Elektrobit PROPSimâ„¢ C8, for wireless channel emulation. A software protocol analyzer, WildPackets Airopeek NX, is used to capture data packets in the testbed from which statistical data characterizing performance such as data rate and Received Signal Strength (RSS) are collected. The relationship between the wireless channel and WLAN performance, under controlled propagation and interference conditions, is analyzed using this RF-isolated multipath testbed. Average throughput and instantaneous throughput variation of IEEE 802.11b and 802.11g WLANs operating in four different channels - a constant channel and IEEE 802.11 Task Group n (TGn) Channel Models A, B, and C - are examined. Practical models describing the average throughput as a function of the average received power and throughput variation as a function of the average throughput under different propagation conditions are presented. Comprehensive throughput models that incorporate throughput variation are proposed for the four channels using Weibull and Gaussian probability distributions. These models provide a means for realistic simulation of throughput for a specific channel at an average received power. Also proposed is a metric to describe the normalized throughput capacity of WLANs for comparative performance evaluation."

The Internet Engineering Task Force (IETF) has recently released routing standards that allow deployment of TCP/IP local area networks (LANs) onboard a moving vehicle and yet maintain permanent connectivity of the onboard LAN to the Internet via a vehicular mobile router. This recent development opens up new opportunities for providing efficient mobile computing for users on the move, especially for commuters traveling on public transports. Supporting real-time communications, e.g. IP Telephony, on-line video on demand, etc., over such onboard mobile networks is the main motivation of this thesis. Due to the volatility of the wireless bandwidth available to connect the moving LAN to the Internet at different locations of the trip, supporting on-line services that require bandwidth guarantees becomes a challenging task. The main problem investigated is how to provide bandwidth guarantee efficiently, effectively, and in a scalable manner in the context of moving onboard networks. To achieve the goal, a systematic approach is taken that involves (i) designing a signalling protocol that allows transparent bandwidth reservation for the aggregate demand of all onboard users in the vehicle, and (ii) proposing effective aggregation and bandwidth reservation policies that aim to maximize the chances of successful reservation and minimize the bandwidth and processing overhead in critical network elements. Mathematical models are derived to evaluate the performance of proposed solutions. These models are validated using discrete event simulation. One important conclusion reached is that onboard mobile communication provides significant aggregation and centralized management opportunities that must be exploited to provide a scalable solution to the bandwidth guarantee problem in mobile communications. The techniques proposed and analyzed in this thesis to exploit such aggregation opportunities constitute the original contribution to knowledge.

Thesis (Ph. D.)--University of Hong Kong, 2007. / Title proper from title frame. Also available in printed format.

Since its introduction in the early 1990s, the quick growth of the World Wide Web (WWW) traffic raises the question of whether past Local Area Network (LAN) packet traces still reflect the current situation or whether they have become obsolete. For this thesis, several LAN packet traces were obtained by monitoring the LAN of a typical academic environment. The tools for monitoring the network were a stand-alone HP LAN Protocol Analyzer as well as the free-ware software tool tcpdump. The main focus was placed on acquiring a low-level overview of the LAN traffic. Thus, it was possible to determine what protocols were mainly used and how the packet sizes were distributed. In particular, this study aimed at establishing the amount of WWW traffic on the LAN, and determining the MIME-Types of this traffic. The results indicate that in a typical academic environment, conventional sources of LAN traffic such as NFS are still predominant, whereas WWW traffic plays a rather marginal role. Furthermore, a large portion of the network packets contains little or no data at all, while another significant portion of the packets have sizes around the Maximum Transfer Unit (MTU). Consequently, research in the networking field has to direct its focus on issues beside the WWW. / Graduation date: 1998

Thesis (Ph.D.) -- Mississippi State University. College of Business and Industry. / Title from title screen. Includes bibliographical references. Also available in print.

In this dissertation, I examine how making infrastructure visible affects users' engagement with that infrastructure, through the case study of home networking. I present empirical evidence of the visibility issues that home networks present to users and how these results informed the design of a prototype called Kermit to visualize aspects of the home network. Through my implementation and evaluation of Kermit, I derive implications for making infrastructure visible in ways that enable end-users to manage and understand the systems they use everyday. I conclude with suggestions for future work for making home networks, and infrastructure more generally, more visible.

Thesis (Ph.D.(Computer Science))--University of Pretoria, 2009. / Abstract in English. Includes bibliographical references.

M. Tech. Information Networks / This dissertation reports on a prototype implementation of an architecture that seamlessly integrates Wireless Body Area Networks with Web services for ubiquitous healthcare service provisioning. The prototype ubiquitous monitoring system proactively collects body physiological signals of remote patients to recommend diagnostic services. The technologies that are based upon Wireless Body Area Networks and Web services can provide ubiquitous accessibility to variety of services by allowing distributed healthcare resources to be massively reused. This contributes to improving quality of healthcare services and shields individuals from physically moving to locations where healthcare services are provided, except in a critical situation. In addition, the technology can reduce costs of healthcare services by allowing individuals to remotely access services to support their healthcare. Especially our system is designed for ubiquitous monitoring of elderly and patients in recovery (or rehabilitation). The Wireless Body Area Networks - Web services architecture is at crossroad of embedded engineering of hardware, software and networking protocols. Testing of the prototype was carried out on enthusiastic volunteers and it has shown to be an efficient, reliable and support state-of-art service provisioning of ubiquitous healthcare monitoring in health sector.

No abstract / Thesis (M.Sc.-Electronic Engineering)-University of Natal, 1992.