No description available.

No description available.

No description available.

In the past, techniques for specifying, verifying and implementing protocols have taken on a somewhat ad hoc (non -uniform) and informal nature. This lack of uniformity has resulted in an abundance of techniques and methodologies for analysing protocols, most of which are applicable to protocols having a small degree of complexity. Typically, different techniques are applied to various stages of a protocol development without an underlying formal basis for their integrated application. As a result, there may be no way to guarantee that subsequent stages of a development represent correct realisations of earlier ones. This thesis aims to address the problem of protocol development stated above by describing unified frameworks within which: 1) A formal theoretical foundation is laid for specifying, verifying and implementing protocols. 2) A knowledge based system is used for the formal development of a certain class of protocols. A number of limitations have been identified in the approach taken for developing the frameworks: a) The lack of 'compositional' expressiveness of the algebraic specification language. This makes it difficult to effectively analyse concurrently executing processes of protocols. b) The lack of support provided for addressing performance related issues. This makes it difficult to compare different protocols to assess their effect with respect to how long they take to achieve some data processing task. c) The protocol derivation algorithm can prove cumbersome in its application and may require a significant amount of domain knowledge (about types of 'primitives') in order to be machine automated. d) The knowledge based framework is currently limited to supporting the development of end-to-end protocols. This however is not a serious problem as the ideas and principles applied in developing these protocols form the basis for work in analysing other types. The above limitations form the basis for future work which will aim to address the problems stated. The thesis is in 5 main parts:- I) A description of various formalisms used in the past, to specify protocols. From this analysis, criteria are developed for assessing the relative merits of these formalisms, with a view towards choosing one such technique to be employed in specifying protocols. ii) A formal development of the protocol which includes a discussion of automatic theorem proving via a syntactic measure known as a trace. iii) A description of a notation with operational semantics developed for specifying and verifying protocols and services. In addition, a method utilising the notation is described whereby a service can be derived from a protocol. iv) A description of a framework within which a protocol may be verified in respect of the service it provides. v) A description of an interactive program (environment) allowing the formal development of a certain class of distributed protocols, such as the ECMA application layer protocol. The originality of this work lies in the: I) development of a methodology for automatically deriving and proving invariant properties of a specification. ii) development of a notation with operational semantics, capable of specifying and verifying distributed protocols and services. iii) identification of a means by which the correspondence between a specification and its implementation may be used as rewrite rules (not necessarily preserving all semantic information) in developing communication protocols. v) numerous algorithms described for addressing safety, liveness and conformity issues, as part of the interactive environment.

Abstract Information and Communication Technology (ICT) solutions (e.g. e-health, telemedicine, e-education) are often viewed as vehicles to bridge the digital divide between rural and urban healthcare centres and to resolve shortcomings in the rural health sector. This study focused on factors perceived to infl uence the uptake and use of ICTs as e-health solutions in selected rural Eastern Cape healthcare centres, and on structural variables relating to these facilities and processes. Attention was also given to two psychological variables that may underlie an individual’s acceptance and use of ICTs: usefulness and ease of use. Recommendations are made with regard to how ICTs can be used more effectively to improve health systems at fi ve rural healthcare centres where questionnaire and interview data were collected: St. Lucy’s Hospital, Nessie Knight Hospital, the Tsilitwa Clinic, the Madzikane Ka-Zulu Memorial Hospital and the Nelson Mandela General Hospital.

No description available.

This thesis concerns the optimization of the routing path in packet-switched computer-communication networks. Computer-communication networks over the past decade are outlined. A glossary of some of the terms used throughout this thesis are introduced. A brief description follows of the advantages of packet switching over the more conventional circuit-switched scheme for information transfer. The important design variables that a network planner is faced with in the design of these networks are discussed. A general design problem is stated and then decomposed into simpler subproblems one of which is the link-capacity assignment problem, which is briefly discussed. The route-assignment problem is identified as being of particular importance and is specified. A network model is introduced and relationships between performance measures, input parameters and constraints that appear in the general design problem are discussed. The routing problem is the formulated and a heuristic routing procedure is suggested as a sub-optimum solution to the problem. Basic routing methods are discussed. The principles of datagram and virtual circuit techniques are explained with reference to the routing of packets throughout the network. The directory routing technique with alternate routing is identified as being a specific requirement and the operation of this technique is explained in more detail. Two basic algorithms are introduced. The first which determines the shortest, second shortest, third shortest, etc., paths between all pairs of nodes in a network. The second which determines from all the paths in the first algorithm, the best alternative paths between all pairs of nodes in a network. A heuristic routing algorithm for establishing routing tables at each of the individual nodes in a packet switched data network is presented. Among the properties of a desirable routing algorithm is that the paths established between all node pairs are such that the average packet delay from source to destination node is minimal. The heuristic-routing algorithm proposed is to-be implemented on a newly proposed SAPONET packet-switching network, with special emphasis on the minimization of the average packet delay of the network. Results are presented and discussed for different combinations of the primary, secondary, tertiary and fourth alternative paths obtained. Finally, results are summarized and areas for further work identified.

The phenomenal emergence of several heterogeneous wireless networks and technologies has allowed users to have access IP services anywhere at anytime from any network with whatever terminal they use. This computing platform has also been driven by the rapid evolution of mobile devices that are equipped with multiple network interfaces and the development of IP based applications. One of the challenging tasks with this Next-Generation Networks (NGN) computing platform is service continuity when users roam around different wireless networks e.g. Wi-Fi, Bluetooth and Cellular networks. This challenge is elevated more when dealing with applications that distribute time continuous data with stringent Quality of Service (QoS) requirements. One of the adaptation methods to ensure service continuity by minimizing flow interruptions when users are mobile is session handoff. The main contribution of the thesis is to present a handoff support system which implements a handoff decision engine using a Multi-Criteria Decision Making (MCDM) method based on a Bayesian Belief Network (BBN) and a handoff execution procedure based on buffering and doublecasting techniques. The handoff support system is built around the following features: 1) It utilises a proxy-based middleware architecture, 2) It uses a BBN based MCDM for handoff decision, 3) It is able to represent the full context information which represents the execution environment, 4) It is able to perform decision making under both certainty and uncertainty, 5) It is able to decide correctly on the target network under dynamic context, 6) It performs decision making in the midst of conflicting, interdependent and constraint criteria, and 7) It uses a profile-based handoff decision to offer personalisation to users. The experimental results showed that when compared with Analytical Hierarchy Process (AHP), the handoff decision method based on BBN performs better on: 1) Modelling of the handoff decision problem and the full representation of the context information, 2) Decision making under uncertainty, 3) Modelling of constraints and interdependent criteria and 4) Support for user preferences. When evaluating the handoff execution, further results revealed that the underlying handoff management strategies provide service continuity by minimising handoff latency and packet losses.

The challenge of parking management has increasingly posed the need for smart solutions. Motorists in today’s busy world seek the best option in locating available parking points. The need for an efficient parking system stems from increased congestion, motor vehicle pollution, driver frustration and fatigue to mention but a few. This study was conducted at a time when the world was experiencing a financial crisis and more than ever motorists needed intelligent parking systems to reduce the cost of gas spent driving around to find parking. Indeed, the time spent driving around would be beneficial if used to do work that would put one at an advantage in the credit recession. The study was also conducted at a time when South Africa was preparing to host the 2010 soccer world cup. In the preparation to manage motor vehicle congestion, this study was a viable solution to manage the expected challenge of parking. This study presents the design and illustrates the performance of an intelligent parking system based on an integrated architecture where (1) Wireless Sensor networks (WSNs) using Small Programmable Object Technology (SPOT) motes are launched into parking places to monitor the activity of the parking area through light intensity sensing and (2) the sensed information is gathered and channeled through a gateway into databases used for parking space visualization and information dissemination over the World Wide Web technology and mobile devices via a Multi Protocol label Switching (MPLS) network. Using an illustrative simulation model of a small parking system built around a new generation of SUNspot motes, the study demonstrates how a real life smart parking system can be deployed to benefit motorists in today’s busy World and serves as a foundation to future work on how this emerging generation of motes can be used to provide better ways of finding parking.

IEEE 802.16 wireless metropolitan area network (WMAN) technology is an improvement on its wireless local area network (WLAN) counterpart, namely IEEE 802.11, in that it provides longer range and higher bandwidth capabilities. More importantly, it specifies a connection-oriented medium access control layer (MAC) and scheduling services to support quality of service (QoS) in IEEE 802.16 networks. However, in the standard, scheduling and connection admission control (CAC) mechanisms are left unspecified, leaving this for network operators to decide. This allows implementers to create market and performance advantages, making it a rich field of research and performance analysis. Typically, researchers studying scheduling and admission control in such wireless networks consider these resource and connection management (RaCM) algorithms in isolation: They investigate (1) schedulers while fixing the admission control processes or using static connection scenarios and (2) admission controllers while fixing the scheduling processes. We hypothesize that there exists an interdependent relationship between RaCM components which is an essential aspect to cross-layer inter-RaCM algorithm design. In order to prove our hypothesis that you cannot consider the scheduler and the CAC in isolation, where it involves the performance of IEEE 802.16 networks, we require a performance model: Analytic modelling is an ideal solution but the system is far too complex. Experimental test beds are expensive, making hardware experimentation another impractical solution. The only other feasible solution is simulation. General simulation environments, such as NS2 and OMNeT++, offer IEEE 802.16 libraries and some degree of development community support. However, for several reasons, as we shall discuss, we developed our own deep simulator – a discrete-event simulation model of an IEEE vertically integrated wireless Internet scenario. In particular, we concentrate our effort on the fixed IEEE 802.16 WMAN (802.16-2004), simulating admission control and scheduling processes exactly. Both the machine model and workload model play an integral part in obtaining useful performance data: Our machine model includes particular MAC and physical layer (PHY) functions of the standard, such as framing, adaptive modulation and coding, fragmentation, and so on, as well as the admission control and scheduling algorithms. For the workload model, we developed a Markov Modulated Arrival Process (MMAP) by combining existing traffic models of different Internet applications, such as VoIP, P2P, etc. Each application is associated with one of the IEEE 802.16 traffic categories (TCs). The MMAP generates both connection– and packet level data, maintaining traffic volume ratios, as reported by previous studies of Internet application traffic volumes. Performance metrics of delay and jitter are calculated per TC connection. This allows a comparison of the quality of experience (QoE) of an individual user for the duration of a connection. At the connection level, we report the blocking probability. By simulating the RaCM with various admission control and scheduling configurations, we were able to show that there is a significant difference in performance when using different CAC and scheduler combinations. Although hardly surprising, it is still proof that one cannot simply consider either in isolation, as is done in various performance studies reported in the literature. This interdependent relationship should be considered when designing complementary admission control and scheduling algorithms.