Thesis (Ph. D.)--University of Florida, 2005. / Title from title page of source document. Document formatted into pages; contains 83 pages. Includes vita. Includes bibliographical references.

Thesis (M.Sc. (Computer Science)) - Rhodes University, 2007.

This thesis describes the design and development of both the hardware and software of an embedded, distributed control system using a LAN infrastructure for communication between nodes. The primary application of this system is for power monitoring and control at Rhodes University. Both the hardware and software have been developed to provide a modular and scalable system capable of growing and adapting to meet the changing demands placed on it. The software includes a custom written Internet Protocol stack for use in the embedded environment, with a small code footprint and low processing overheads. There is also Linux-based control software, which includes a web-based device management interface and graphical output. Problems specific to the application are discussed as well as their solutions, with particular attention to the constraints of an embedded system.

There is little literature available that is specific to the use of wireless local area network [WLAN) security among small, medium and micro enterprises (SMMEs) in South Africa. This research study developed a framework which may be used by SMMEs for the purposes of securing their WLANs. In view of the fact that the aim of the study was to develop a system for improving information technology security, the study followed a design science approach. A literature review was conducted on security control framework standards and WLAN technologies. The needs of SMMEs regarding WLANs were also established. The result of this process was an artefact in the form of a WLAN Security Control Framework for securing WLANs for SMMEs in South Africa. The suitability of the framework was validated by means of a focus group.

This thesis is concerned with analytical modeling of Wireless Local Area Networks (WLANs) that are based on IEEE 802.11 Distributed Coordination Function (DCF). Such networks are popularly known as WiFi networks. We have developed accurate analytical models for the following three network scenarios: (S1) A single cell WLAN with homogeneous nodes and Poisson packet arrivals, (S2) A multi-cell WLAN (a) with saturated nodes, or (b) with TCP-controlled long-lived downloads, and (S3) A multi-cell WLAN with TCP-controlled short-lived downloads. Our analytical models are simple Markovian abstractions that capture the detailed network behavior in the considered scenarios. The insights provided by our analytical models led to two applications: (i) a faster “model-based'” simulator, and (ii) a distributed channel assignment algorithm. We also study the stability of the network through our Markov models. For scenario (S1), we develop a new approach as compared to the existing literature. We apply a “State Dependent Attempt Rate'” (SDAR) approximation to reduce a single cell WLAN with non-saturated nodes to a coupled queue system. We provide a sufficient condition under which the joint queue length Markov chain is positive recurrent. For the case when the arrival rates into the queues are equal we propose a technique to reduce the state space of the coupled queue system. In addition, when the buffer size of the queues are finite and equal we propose an iterative method to estimate the stationary distribution of the reduced state process. Our iterative method yields accurate predictions for important performance measures, namely, “throughput'”, “collision probability” and “packet delay”. We replace the detailed implementation of the MAC layer in NS-2 with the SDAR contention model, thus yielding a ``model-based'' simulator at the MAC layer. We demonstrate that the SDAR model of contention provides an accurate model for the detailed CSMA/CA protocol in scenario (S1). In addition, since the SDAR model removes much of the details at the MAC layer we obtain speed-ups of 1.55-5.4 depending on the arrival rates and the number of nodes in the single cell WLAN. For scenario (S2), we consider a restricted network setting where a so-called “Pairwise Binary Dependence” (PBD) condition holds. We develop a first-cut scalable “cell-level” model by applying the PBD condition. Unlike a node- or link-level model, the complexity of our cell-level model increases with the number of cells rather than with the number of nodes/links. We demonstrate the accuracy of our cell-level model via NS-2 simulations. We show that, as the “access intensity” of every cell goes to infinity the aggregate network throughput is maximized. This remarkable property of CSMA, namely, “maximization of aggregate network throughput in a distributed manner” has been proved recently by Durvy et al. (TIT, March, 2009) for an infinite linear chain of nodes. We prove it for multi-cell WLANs with arbitrary cell topology (under the PBD condition). Based on this insight provided by our analytical model we propose a distributed channel assignment algorithm. For scenario (S3), we consider the same restricted network setting as for scenario (S2). For Poisson flow arrivals and i.i.d. exponentially distributed flow sizes we model a multi-cell WLAN as a network of processor-sharing queues with state-dependent service rates. The state-dependent service rates are obtained by applying the model for scenario (S2) and taking the access intensities to infinity. We demonstrate the accuracy of our model via NS-2 simulations. We also demonstrate the inaccuracy of the service model proposed in the recent work by Bonald et al. (SIGMETRICS 2008) and identify the implicit assumption in their model which leads to this inaccuracy. We call our service model which accurately characterizes the service process in a multi-cell WLAN (under the PBD condition) “DCF scheduling” and study the “stability region” of DCF scheduling for small networks with single or multiple overlapping “contention domains”.

M.Com. (Computer Auditing) / With all the technology available in today’s world, people have become more connected to each other as well as to the world around them. This has been echoed by Rutledge (2009:1), who stated: “Emerging technologies are linking the world, but we no longer need wires and cables to connect people. People are no longer trapped by geography. We are, however, facing a digital tsunami as communications technology becomes cheaper, simpler, and more culturally-acceptable.” The new wireless technology has become an aid to most organizations, making networking simpler, cheaper and more effective, and has not only changed the way businesses operates but has changed the entire world of communications. It has not only caused a change in technology, but a change in the way of life. This is emphasized by Lawlor (2007:3), who stated: “Information technology has been a major driving force behind globalization and that information technology has now become a key component of a corporation’s global business strategy.” It is evident that the use of wireless technologies has changed the mode in which work is carried out and the manner in which communication takes place today. It has made it easier, more effective and efficient than before with wired technology. Wireless networks provide computing suppleness. It aids employees and individuals to take advantage of mobile networking for e-mail, Internet access, and sharing files regardless of where they are in the office or in a local area network (hereafter LAN). The advantage of the wireless setting is that it can be moved around at will, with no need for cables, leaving employees free to work from anywhere...

Includes bibliographical references (leaves 80-84). / Recent times has seen a tremendous increase in the deployment and use of 802.11 Wireless Local Area Networks (WLANs). These networks are easy to deploy and maintain, while providing reasonably high data rates at a low cost. In the paradigm of Next-Generation-Networks (NGNs), WLANs can be seen as an important access network technology to support IP multimedia services. However a traditional WLAN does not provide Quality of Service (QoS) support since it was originally designed for best effort operation. The IEEE 802. 11e standard was introduced to overcome the lack of QoS support for the legacy IEEE 802 .11 WLANs. It enhances the Media Access Control (MAC) layer operations to incorporate service differentiation. However, there is a need to prevent overloading of wireless channels, since the QoS experienced by traffic flows is degraded with heavily loaded channels. An admission control scheme for IEEE 802.11e WLANs would be the best solution to limit the amount of multimedia traffic so that channel overloading can be prevented. Some of the work in the literature proposes admission control solutions to protect the QoS of real-time traffic for IEEE 802.11e Enhanced Distributed Channel Access (EDCA). However, these solutions often under-utilize the resources of the wireless channels. A measurement-aided model-based admission control scheme for IEEE 802.11e EDCA WLANs is proposed to provide reasonable bandwidth guarantees to all existing flows. The admission control scheme makes use of bandwidth estimations that allows the bandwidth guarantees of all the flows that are admitted into the network to be protected. The bandwidth estimations are obtained using a developed analytical model of IEEE 802.11e EDCA channels. The admission control scheme also aims to accept the maximum amount of flows that can be accommodated by the network's resources. Through simulations, the performance of the proposed admission control scheme is evaluated using NS-2. Results show that accurate bandwidth estimations can be obtained when comparing the estimated achievable bandwidth to actual simulated bandwidth. The results also validate that the bandwidth needs of all admitted traffic are always satisfied when the admission control scheme is applied. It was also found that the admission control scheme allows the maximum amount of flows to be admitted into the network, according the network's capacity.

Master of Science

Bibliography: pages 61-66. / This dissertation addresses system architecture concepts for the implementation of real-time distributed systems. In particular, it addresses the requirements of a specific mission and real-time critical distributed system application as this exemplifies most of the issues of concern. Of specific significance is the integration of real-time distributed data services into a platform-wide Information Management Infrastructure. The dissertation commences with an overview of the system-level allocated requirements. Derived requirements for an Information Management Infrastructure (IMI) are then determined. A generic system architecture is then presented in terms of the allocated and derived requirements. A specific topology, based on this architecture, as well as available technology, is described. The scalability of the architecture to -different platforms, including non-surface platforms, is discussed. As financial considerations are an important design driver and constraint, some anticipated order-of-magnitude system acquisition costs for a range of system complexities and configurations are briefly reviewed. Finally some conclusions and recommendations within the context of the allocated and derived requirements, as well as the RSA's politico-economic environment, are offered.

Bibliography: pages 77-80. / This is a study of the simulated performance of two local area networks, Ethernet and the MAP network, respectively based on the IEEE standards 802.3 and 802.4. The simulation language chosen is of the discrete event type rather than the more usual analytical model. This is done in order to observe the interaction between the various entities of a network in order to gain a better understanding of the method of operation of such a system. The performance demanded of a node entity by the networks is determined. The performance of some commercially available hardware is derived from manufacturer's specifications and compared with that required by the network. It is found that there is a significant disparity, with the network requirements far exceeding that of the hardware capabilities. The simulation models developed are used to determine the performance of the networks both with and without the limitations imposed by currently available hardware. While the inclusion of the hardware performance causes little ·loss in performance for the Ethernet network, it has a highly detrimental effect on that of the MAP network. A possible solution is found to this limitation which requires minimal change to the existing protocol. The conclusions reached are that with currently available hardware a group of nodes are able to fully utilise the performance of the Ethernet LAN although a single pair of nodes is unable to do so. With regard to the MAP network, the network performance is limited by that of the node performance although this can be offset to a certain extent by careful choice of one of the protocol parameters, or modification of the hardware design.