Browsing by Author "Ventura, M J"

Now showing 1 - 12 of 12
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    APIS : a real-time message-oriented middleware
    (2001) Steyn, Manie C; Ventura, M J
    This thesis presents an investigation and evaluation of a Real-Time Message-Oriented Middleware (MOM) implementation using commercial off-the-shelf (COTS) software components. The Application Interface Services (APIS) is an implementation of a real-time MOM that provides network services to sub-systems of a large-scale distributed system. It is shown that the characteristics of a MOM are well suited to a real-time message distribution application and that APIS, as an implementation of a real-time MOM, can provide a heterogeneous network interlace to subsystems of a distributed real-time nature. This simplifies the task of implementing information exchange and provides a definitive boundary for assigning responsibility during system design and development.
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    The application of forward error correction techniques in wireless ATM
    (1999) McLuckie, Craig Ian; Ventura, M J
    The possibility of providing wireless access to an ATM network promises nomadic users a communication tool of unparalleled power and flexibility. Unfortunately, the physical realization of a wireless A TM system is fraught with technical difficulties, not the least of which is the problem of supporting a traditional ATM protocol over a non-benign wireless link. The objective of this thesis, titled "The Application of Forward Error Correction Techniques in Wireless ATM' is to examine the feasibility of using forward error correction techniques to improve the perceived channel characteristics to the extent that the channel becomes transparent to the higher layers and allows the use of an unmodified A TM protocol over the channel. In the course of the investigation that this dissertation describes, three possible error control strategies were suggested for implementation in a generic wireless channel. These schemes used a combination of forward error correction coding schemes, automatic repeat request schemes and interleavers to combat the impact of bit errors on the performance of the link. The following error control strategies were considered : 1. A stand alone fixed rate Reed-Solomon encoder/decoder with automatic repeat request. 2. A concatenated Reed-Solomon, convolution encoder/decoder with automatic request and convolution interleaving for the convolution codec. 3. A dynamic rate encoder/decoder using either a concatenated Reed-Solomon, convolution scheme or a Reed-Solomon only scheme with variable length Reed-Solomon words.
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    ATM network impairment to video quality
    (2000) Wong, Alfred Ching Hong; Ventura, M J
    Includes bibliographical references
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    ATOM : a distributed system for video retrieval via ATM networks
    (1999) Roux, Matthew John; Ventura, M J
    The convergence of high speed networks, powerful personal computer processors and improved storage technology has led to the development of video-on-demand services to the desktop that provide interactive controls and deliver Client-selected video information on a Client-specified schedule. This dissertation presents the design of a video-on-demand system for Asynchronous Transfer Mode (ATM) networks, incorporating an optimised topology for the nodes in the system and an architecture for Quality of Service (QoS). The system is called ATOM which stands for Asynchronous Transfer Mode Objects. Real-time video playback over a network consumes large bandwidth and requires strict bounds on delay and error in order to satisfy the visual and auditory needs of the user. Streamed video is a fundamentally different type of traffic to conventional IP (Internet Protocol) data since files are viewed in real-time, not downloaded and then viewed. This streaming data must arrive at the Client decoder when needed or it loses its interactive value. Characteristics of multimedia data are investigated including the use of compression to reduce the excessive bit rates and storage requirements of digital video. The suitability of MPEG-1 for video-on-demand is presented. Having considered the bandwidth, delay and error requirements of real-time video, the next step in designing the system is to evaluate current models of video-on-demand. The distributed nature of four such models is considered, focusing on how Clients discover Servers and locate videos. This evaluation eliminates a centralized approach in which Servers have no logical or physical connection to any other Servers in the network and also introduces the concept of a selection strategy to find alternative Servers when Servers are fully loaded. During this investigation, it becomes clear that another entity (called a Broker) could provide a central repository for Server information. Clients have logical access to all videos on every Server simply by connecting to a Broker. The ATOM Model for distributed video-on-demand is then presented by way of a diagram of the topology showing the interconnection of Servers, Brokers and Clients; a description of each node in the system; a list of the connectivity rules; a description of the protocol; a description of the Server selection strategy and the protocol if a Broker fails. A sample network is provided with an example of video selection and design issues are raised and solved including how nodes discover each other, a justification for using a mesh topology for the Broker connections, how Connection Admission Control (CAC) is achieved, how customer billing is achieved and how information security is maintained. A calculation of the number of Servers and Brokers required to service a particular number of Clients is presented. The advantages of ATOM are described. The underlying distributed connectivity is abstracted away from the Client. Redundant Server/Broker connections are eliminated and the total number of connections in the system are minimized by the rule stating that Clients and Servers may only connect to one Broker at a time. This reduces the total number of Switched Virtual Circuits (SVCs) which are a performance hindrance in ATM. ATOM can be easily scaled by adding more Servers which increases the total system capacity in terms of storage and bandwidth. In order to transport video satisfactorily, a guaranteed end-to-end Quality of Service architecture must be in place. The design methodology for such an architecture is investigated starting with a review of current QoS architectures in the literature which highlights important definitions including a flow, a service contract and flow management. A flow is a single media source which traverses resource modules between Server and Client. The concept of a flow is important because it enables the identification of the areas requiring consideration when designing a QoS architecture. It is shown that ATOM adheres to the principles motivating the design of a QoS architecture, namely the Integration, Separation and Transparency principles. The issue of mapping human requirements to network QoS parameters is investigated and the action of a QoS framework is introduced, including several possible causes of QoS degradation. The design of the ATOM Quality of Service Architecture (AQOSA) is then presented. AQOSA consists of 11 modules which interact to provide end-to-end QoS guarantees for each stream. Several important results arise from the design. It is shown that intelligent choice of stored videos in respect of peak bandwidth can improve overall system capacity. The concept of disk striping over a disk array is introduced and a Data Placement Strategy is designed which eliminates disk hot spots (i.e. Overuse of some disks whilst others lie idle.) A novel parameter (the B-P Ratio) is presented which can be used by the Server to predict future bursts from each video stream. The use of Traffic Shaping to decrease the load on the network from each stream is presented. Having investigated four algorithms for rewind and fast-forward in the literature, a rewind and fast-forward algorithm is presented. The method produces a significant decrease in bandwidth, and the resultant stream is very constant, reducing the chance that the stream will add to network congestion. The C++ classes of the Server, Broker and Client are described emphasizing the interaction between classes. The use of ATOM in the Virtual Private Network and the multimedia teaching laboratory is considered. Conclusions and recommendations for future work are presented. It is concluded that digital video applications require high bandwidth, low error, low delay networks; a video-on-demand system to support large Client volumes must be distributed, not centralized; control and operation (transport) must be separated; the number of ATM Switched Virtual Circuits (SVCs) must be minimized; the increased connections caused by the Broker mesh is justified by the distributed information gain; a Quality of Service solution must address end-to-end issues. It is recommended that a web front-end for Brokers be developed; the system be tested in a wide area A TM network; the Broker protocol be tested by forcing failure of a Broker and that a proprietary file format for disk striping be implemented.
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    Design and implementation of a functional WATM test bed to study the performance of handoff schemes
    (2003) Smith, Farouk; Ventura, M J
    The focus of this research is on the design and implementation of a WATM functional architecture in order to facilitate a seamless handoff. The project includes an experimental implementation of the WATM network. This required the building of a prototype WATM network with existing ATM switches and implementing handover protocol schemes at both the access and network sides.
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    A framework for fast handoff schemes in wireless ATM networks
    (2003) Elbergali, Jamal Ramadan; Ventura, M J
    In this research, we focus on providing a framework that extends the fixed ATM standard to support user mobility in future WATM networks. The WATM architecture allows for the migration of fixed ATM networks without major modifications. Thus most of the mobility functions are implemented on the wireless access network. The most important component supporting mobility in a cluster is the Mobility Enhanced Switch (MES). We propose using direct links between adjacent MESs to support Permanent Virtual Channels (PVCs) in order to facilitate fast inter-cluster handoffwith minimum handofflatency. This research addresses a framework on handoff mobility by proposing three fast handoff re-routing schemes based on the support of PVCs.
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    HEAVEn : the design and implementation of a scalable ATM based distributed virtual environment
    (2003) Dennis, Kevin Stuart; Ventura, M J
    Bibliography: leaves 131-151.
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    The implementation of a LAN
    (1988) McGrath, Quintin Peter; Bradlow, H S; Ventura, M J
    The subject of this thesis concerns the development of a Local Area Network (LAN) for the Department of Electrical and Electronic Engineering at the University of Cape Town. Motivation for this project was as a result of the ever increasing demands placed on the department's micro-computer training facilities by larger student intakes. The original training system consisted of a PDP 11/23 mini-computer connected via 9600 baud asynchronous links to 11 U.C.T. built micro-computers. This network topology was limiting in three ways: 1. It was slow because of the 9600 baud links and because the PDP was doing a large proportion of the processing.2. High-leve 1 software development tools for the PDP were too expensive and would over-load the computer. Because the micro-computers have no operating system but only an "in-house" monitor program which is not able to support any high-level language utility, all high-level software tools would have to be individually developed for this particular environment. 3. Switching was impractical. Because the PDP was the hub of the network all communication between computers had. to pass through it. This switching would lead to a greater processing load on the PDP, thus further degrading its performance. A two pronged attack was used to overcome these weaknesses: firstly, by designing a high-speed (1 Mbps) LAN to provide communications between a PDP 11/23 and up to 30 U.C.T. built micro-computers, faster inter-computer communication as well as switching and resource sharing was facilitated. Secondly, by customizing an operating system for the micro-computers, standard high-level software development tools could be used on these computers, consequently reducing the PDP's processing load.
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    Network time : synchronisation in real time distributed computing systems
    (1998) Crellin, Kenneth Thomas; Ventura, M J
    In the past, network clock synchronization has been sufficient for the needs of traditional distributed systems, for such purposes as maintaining Network File Systems, enabling Internet mail services and supporting other applications that require a degree of clock synchronization. Increasingly real time systems arc requiring high degrees of time synchronization. Where this is required, the common approach up until now has been to distribute the clock to each processor by means of hardware (e.g. GPS and cesium clocks) or to distribute time by means of an additional dedicated timing network. Whilst this has proved successful for real time systems, the use of present day high speed networks with definable quality of service from the protocol layers has lead to the possibility of using the existing data network to distribute the time. This thesis demonstrates that by using system integration and implementation of commercial off the shelf (COTS) products it is possible to distribute and coordinate the time of the computer time clocks to microsecond range. Thus providing close enough synchronization to support real time systems whilst avoiding the additional time, infrastructure and money needed to build and maintain a specialized timing network.
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    PC-based bit error rate analyser for a 2 Mbps data link
    (1988) Bayley, Gwain; Ventura, M J
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    Performance evaluation of a communication network
    (1995) Ncube, Ariage T; Ventura, M J
    This work uses a simulation package to analyze the performance of a specific X.25 Value Added Communication Network (VAN), comprising a Network Administrator and a cluster of Network Concentrators (NCs). Detailed models of the network elements are developed, and system performance is analyzed in terms of network response time for the terminal users communicating across the network, identification of areas of bottlenecks in the NC system, and NC system throughput. The througput parameter is represented by the percentage of the output traffic to the load offered from the network of terminals. The performance of the Network Administrator system is also modeled, focusing particularly on the automatic restoration of service to failed NCs through downloading of operating software sets over the X.25 network. The final part consists of a model of a modification of the network manager components of the network as proposed in the DM upgrade project. In this section, NC loading time is again the desired performance indicator. It is shown that there is no noticeable improvement in this parameter between the original system and the proposed upgrade, both systems having a minimum loading time of about 3.5 to 6 minutes for a small network.
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    Performance of a ATM Lan switching fabric
    (1998) Yu, Lianghong; Ventura, M J
    This thesis provides a focus on the architecture of a high-speed packet switching fabric and its performance. The switching fabric is suited for existing transparent protocols, based on Asynchronous Transfer Mode (ATM) technology and standards in an environment of Local Area Network (LAN). A high-speed switching fabric architecture which adopts Time Division mode and bases on a shared medium approach is proposed. This is an architecture for nonblocking performance, no congestion and high reliability. Its principle for performance is a method of sequentially scheduling the inputs and the transferring of bits in parallel. To study the performance of the switching fabric architecture one uses OPNET communication simulation software. Some parameters including the throughputs, the transfer (the switching fabric) delay, the switching overflow and the packet size in the buffer (the input buffer and the output buffer) are implemented through the simulation. And finally, an analysis for the results of the simulation for local ATM IDS fabric architecture is discussed. The results display an architecture that provides a rational design with some expected characteristics.