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An overview of the computer networks currently being developed is presented. Three types of network design are distinguished - packet switching, line switching and Newhall loops. Reference is made to several models developed during the design of these networks, but only those concerned with packet switching are described in detail. A gueueing model emerges as a feasible alternative to the more expensive simulation models. This model is developed to include the basic logic of the message switching centres (nodes) and used as the backbone to a heuristic procedure that considers limited capacity buffers and blocking at the nodes. Key words and phrases: Data transmission, computer nets, packet switching, switching centre, interactive computation, resource sharing, queueing network, Markovian queue, steady state. / Science, Faculty of / Computer Science, Department of / Graduate

M.Comm. / In manufacturing companies where raw material is transformed into an endproduct, data pertaining to that transformation process are transported from the physical machine (workstation) to a central database and visa versa. To ensure a successful end-product creation, the company needs to ensure that the data being transported is correct, accurate and trustworthy at all times. As unreliable data seems to be a general problem for large manufacturing companies an investigation was launched to establish what integrity problems are being experienced and possible solutions to these problems in manufacturing companies such as Columbus Stainless Steel. On completion of the investigation it was found that the main causes for late deliveries and data fixes being performed was that the data being transmitted at the source was not always the same data received at the destination, hence a lack of data integrity during data transmission was identified. As it was decided to reduce or eliminate the integrity causes rather than correcting the incorrect results the data transportation process was analyzed. During the analysis the main causes for data integrity problems (errors) were identified. In the environment being investigated, data strings (messages) were created at the workstation and then transported via the use of a transporter (protocol) over an established network to the destination database. The more complex the contents of the message (data string), the more advanced features were needed within the functionality of the protocol to ensure the accurate and correct transmission and processing. Once the main causes for these data integrity errors were identified the investigation was broadened to incorporate the search for various protocols with the ability to reduce or eliminate the causes identified previously.

M.Ing. (Electrical Engineering Science) / In today's rapidly changing technological environment, more and more importance is being attached to producing products as small as possible to save space as well as materials. Systems today use a wide range of signals, from those used to transmit energy, to small signal electronic signals used for control purposes. As these signals are not very compatible, they must each have their own cable harness to prevent unwanted interference between the signals. As a first step to reducing system size, the control signals (or any signal containing information) may be transmitted on the power transmission line, using techniques investigated in this dissertation. Systems using the same conductors for simultaneous energy and data transmission have many applications ranging from high tech systems to low cost rural communication. Examples of systems where this technology can be applied include: (a) distributed high frequency power systems, where switching of remote equipment can be done from a central point; (b) communication and control in harsh environments such as mining complexes, where switching of fans and motors for example can be done from a central point, while a communication network can be established by placing the information signals on the power cables; and (c) flexible manufacturing cells, where robots can be controlled via the power transmission harness. On the other hand, rural communication systems can be realised over the 50 Hz utility transmission network in remote areas. Such a system has the advantage of offering a low cost solution to providing access to communication to a large number of people spread over a large area. The work described In this dissertation covers two systems, firstly information transmission over the 50 Hz utility network and secondly, the design of a high frequency distributed power system utilising simultaneous information transmission on the transmission line.The first three chapters give an introduction to the technology and discuss the theory which must be applied to make simultaneous energy and information transmission over one conductor viable. Chapter 4 discusses the 50 Hz utility network as an information distribution network. The advantages and disadvantages are discussed, while some solutions are proposed how the disadvantages can be overcome. Chapter 5 discusses a high frequency distributed power system using simultaneous information transmission. The converter design is discussed, while some special design considerations are given which are essential to successful simultaneous information transmission in such a distributed system. To help with the design of the converter used, a simulation was carried out to predict the voltage and current waveforms in such a converter, the results of which can be seen in Appendix B.. The aim of simultaneously transmitting energy and information on the same transmission line was realised in both cases. In the 50 Hz system it was shown that adding external networks to guide the information carrier around obstacles such as 50 Hz power transformers improved the information transmission. A distributed power system however does not need external elements as long as the design of transformers follows the special considerations as described in chapter 5.

Master of Science

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