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Magister Scientiae - MSc / This thesis proposed and presented technical details of new probabilistic metrics of trust in the links wireless ad hoc networks for unobservable communications. In covert communication networks, only the end nodes are aware of the communication characteristics of the overall path. The most widely used protocols of ad hoc networks was overviewed. The routing protocols of ad hoc networks with trust considerations and select Destination Sequence Routing, a protocol that can be used in distributed ad hoc network settings for path discovery, was also reviewed. It establishes a path through which all packets sent by a source must pass to the destination. The end nodes are responsible for examining the statistics of the received packets and deriving inferences on path feature variations which are used for computing new trust metrics. When a path is judged not trustworthy based on the metrics, the Destination Sequence Routing is informed to undertake a new trusted path discovery between the end points. The thesis added a new feature based on the quality of service parameters of the path to create trust in the links in recognition of attacks. / South Africa

This thesis provides in-depth information on the high speed optical transport requirements for the Square Kilometre Array. The stringent data rates as well as timing and synchronization requirements are dealt with respect to the optical fibre technology. Regarding the data transport, we draw a clear comparison between a typical telecommunication access network and a telescope network. Invoking simulations and experiments on the field and laboratory test bed, we successfully implement a suitable telescope network using vertical cavity surface emitting laser (VCSEL) technology. Polarization effects on the KAT-7 telescope network, an operational prototype for the SKA is studied so as to estimate the expected effect in the MeerKAT telescope with transmission distances _ 12 km. The study further relates the obtained values to the expected impact on the distribution of the time and frequency reference in the MeerKAT array. Clock stability depends on the differential group delay (DGD) and polarization stability. On a 10:25 km link that includes the riser cable a DGD of 62:1 fs was attained. This corresponds to a polarization mode dispersion (PMD) coefficient of 19:4 fs=km1=2. This is a low PMD value considering telecommunication network. The PMD value is within the allowed budget in the telescope network. However, this may not be the case at longer baselines extending to over 1000 km as expected in SKA 2. The fibre's deployment contribution to the DGD is measured by comparing the deployed fibre to the undeployed of equal lengths. On the 10:25 km deployed single mode fibre, the maximum and mean DGDs measured were 217:7 fs and 84:8 fs respectively. The undeployed fibre of similar type and equal length, gave a maximum and minimum DGDs of 58:6 fs and 36:3 fs respectively. The deployment is seen to increase the maximum and minimum DGDs by factors of 3.7 and 2.3 respectively. This implies that fibre deployment is very critical in ensuring the birefringence is minimized. Polarization fluctuation recorded a maximum of 180o during the 15 hour real time astronomer use of the antenna. To ascertain the contribution of the riser cable, state of polarization (SOP) of the buried section of the single mode fibre in the link was established. A maximum SOP change of 14o over 15 hour monitoring was measured. From the stability realized on the buried section of the fibre, the change in polarization is contributed by the riser cable. The fluctuation in polarization can cause the phase of a clock signal to drift between the birefringent axes by an equal amount corresponding to DGD. We experimentally demonstrate how polarization stabilization can be attained using the polarization maintaining fibre. We also demonstrate the applicability of VCSEL technology in the SKA unidirectional data flow especially for shorter baselines < 100 km. The VCSEL is a low cost light source with attractive advantages such as low power consumption, high speed capabilities and wavelength tuneability. This work entails the use of traditional amplitude modulation commonly known as non-return-to-zero (NRZ) on-off keying (OOK) because of its simplicity and cost. For the MeerKAT typical distances, we show that even in a worst case scenario, the use of VCSEL on different fibres in MeerKAT distance is achievable. Using the impairment reduction approach, we successfully manage to achieve transmission distance beyond MeerKAT. Several in-line dispersion compensation mechanisms in telecommunication have been successfully employed. The work focused on the use of negative dispersion fibre to mitigate the chromatic dispersion effects in the optical fibre. The inverse dispersion fibre (IDF) is proposed for compensation in the conventional zero dispersion wavelength fibres, G.652 that are used at the third window. Similarly, the chromatic dispersion compensation of non-zero dispersion shifted fibre (NZDSF) is experimentally demonstrated using negative dispersion submarine reduced slope (SRS), G. 655 (-). With dispersion management, we demonstrate how transmissions beyond MeerKAT baselines can be achieved error free. A systematic investigation of the use of distributed Raman amplification to overcome the attenuation losses is provided. High on-off gains of up to 15 dB, 8 dB and 5 dB for bidirectional, forward and backward pumping respectively is achieved on a 25 km Raman optimized NZDSF-Reach fibre. Combined dispersion mitigation technique and low noise distributed Raman amplification, up to about 80 km transmission was achieved on a 4:25 Gbps modulated VCSEL using a single pump. Using bidirectional pumping, more than 100 km of transmission was achieved error free. The high gains enhance the VCSEL transmission distance. We further suggest a novel way of using the Raman pump to distribute the clock signal while amplifying the data signal streaming the astronomical data from the remote placed telescope receivers. In summary, the work presented in this thesis has demonstrated the potential use of VCSEL technology for data collection in the telescope array. We have studied the optical effects and mitigation so as to improve the clock and data transmission. This work is relevant and valuable in providing SKA with VCSELs, an option for extremely high network performance at reasonable costs.

This thesis describes a design for a multi-computer communication system using a shared memory. The design is implemented using the Motorola EXORset 30/DS35 development systems. The primary use for the shared memory is to act as a message center similar to a mailbox, where each computer can leave messages for other computers and also pick up messages from other computers. Status word residing in shared memory, called semaphore, are used to indicate the condition of the mailbox. Each computer polls unique semaphores associated with unique message transfers when requesting to send a message or to receive a message.

Compounded codes are used for representing voice data in digital communication systems. This thesis addresses the use of the Mu-law companding algorithm in a system optimized for conferencing. A procedure for determining the degree of compression for a variable number of conferees and design equations for implementing a table-lookup scheme using read-only-memories are presented.

M.Ing. (Electrical & Electronic Engineering) / This thesis investigates the problems associated with providing end to end in-service performance monitoring on leased line data networks. These problems are of both practical and theoretical nature. A solution to this problem is presented and is based on linear block coding using some overhead bandwidth available within the channel. The coding scheme relies on the characteristics of shortened cyclic codes. A method is given to obtain the undetected error probability for an arbitrary code generation polynomial with a specified degree of shortening. References to the literature explain why this type of calculation is not straightforward. This method is used to compare various candidate codes. A method is discussed which facilitates rapid isolation of groups of favourable candidate codes for further study. Software is developed to aid in the code selection process and optimum codes are selected for leased line application. It is shown that in most cases improvements in undetected error probability are achievable, when comparison is made to previously published codes, proposed for error detection. This is because code generators optimum at their published or natural coding rate are seldom optimum at the rate which results from shortening the code.

M.Comm. / In today's society everyone is dependent on information for decision making, and a big part of the information is provided via telecommunication lines. Telecommunication is the unseen and unsung hero when it comes to information transfer. It is no wonder that telecommunication service providers are striving to give better and faster service almost daily. Furthermore because of the competitive nature of the telecommunications arena, service providers are striving to get the best performance from their telecommunications links. It has thus become more important to provide excellent service and guaranteed performance above anything else. The purpose of this study is to determine what kind of information is needed by the management of a telecommunications service provider to make business or strategic decisions. Questionnaires and interviews were used in this study to determine what kind of information is needed by the managers and the decision makers in the management of the telecommunication network. The basis of the study was provided through the examination of what a telecommunication network consists of, and the information that is needed to run such a network. An additional feature was that there is already a network monitoring system working practically. This system was used to measure the success of telecommunication network management and to determine what other factors should be catered for when a total telecommunication management network is evaluated.

Information system requirements determination is a key area in management information systems research that includes the problems of requirements specification, requirements elicitation, and user involvement. The combination of these three problems is a research area which we call the group approach to information system requirements determination. The main contribution of this research is a model to be used for the problem of fitting existing computer aids to this research area and a set of methods for solving the usability and configuration problems when using such computer aids. The usability problem is that of determining whether a set of computer aids can be used effectively in accomplishing the task of requirements determination. The configuration problem is that of selecting a minimum collection of funtionalities necessary for economically supporting all aspects of requirements determination. Electronic meeting systems are the general category of computer aids that we are interested in applying to the task. In particular, the GroupSystems electronic meeting system developed at The University of Arizona is used as a case in this research. Characteristics of the requirements determination task and profiles of GroupSystems tools are combined into our model for fitting computer aids to a given task. We then derive the answers regarding the usability and configuration of GroupSystems in the group approach to information system requirements determination. We also compare the derived configurations to the GroupSystems tools used in an authentic case. The main points of this research include: (1) proposal of the concept of fitting computer aids to, instead of developing new computer aids for, a task area; (2) proposal of a model for fitting computer aids via a classification of information types; (3) analysis of the natures of the fitting model and the usability and configuration problems; (4) proposal of approximation methods for solving the configuration problem; (5) analysis of the task area--the group approach to information system requirements determination; (6) analysis of the use of GroupSystems in the task area by applying the proposed fitting model and approximation methods; and (7) demonstration of the usefulness of the fitting model and approximation methods by analyzing an authentic case of using GroupSystems tools.

In the two years 1989-1991 the environment of Poland's telecommunications was fundamentally transformed. This dissertation is an exploratory case study addressing four principal aspects of that country's changing telecommunications: (1) telecommunication regime or the structure of rules in which telecommunication systems function; (2) telecommunication services, defined as the means and methods of communicating from a distance by processing and relaying an electro-magnetic signal (categorized into telephone, mobile, data-messaging, information, data-carrier, and entertainment); (3) telecommunication equipment, or markets for switching, transmission and terminal equipment; and (4) telecommunication subscribers, or principal characteristics of the customer-base in the residential, professional, rural and urban market segments. Each aspect is examined for the purpose of capturing the on-going change. The dissertation identifies the principal agents of change and maps the new conditions onto the models developed by Cowhey and Aronson. Institutional pluralism, market competition, shortage alleviation and market restructuring have transformed Poland's telecommunication environment from the scarcity model to a version of the boutique model.