Browsing by Author "Ventura, M J E"

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    Real-time distributed system architecture using local area networks
    (1992) Young, Richard; Ventura, M J E
    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.
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    A session layer for the X.400 message handling system
    (1990) Van der Westhuizen, Eugene Daniel; Ventura, M J E
    The CCITT X.400 Message Handling System resides in the Application Layer of the seven-layer Reference Model for Open Systems Interconnection. It bypasses the services of the Presentation Layer completely to interact directly with the Session Layer. The objectives of this thesis are to show how the general Session Layer may be tailored to be minimally conformant to the requirements of X. 400; to produce a formal specification of this session layer; and to show how this session layer may be implemented on a real system. The session services required by X. 400 are those of the Halfduplex, Minor Synchronization, Exceptions and Activity Management functional units of the CCITT X.215 Session Service Definition. These services, and particularly their use by X.400, are described in detail. State tables describing these services are derived from the general session service state tables. Those elements of the CCITT X. 225 Session Protocol Specification which are required to provide only those services required by X. 400 are described in detail. State tables describing this session protocol are derived from the general session protocol state tables. A formal specification of the session layer for X.400 is presented using the Formal Description Technique Estelle. This specification includes a complete session entity, which characterizes the entire session layer for X.400. A session entity for supporting X.400 is partially implemented and interfaced to an existing X.400 product on a real system. Only the Session Connection Establishment Phase of the session protocol is implemented to illustrate the technique whereby the entire session protocol may be implemented. This implementation uses the C programming language in the UNIX operating system environment.
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    Using fuzzy logic for congestion control at the user-network interface of asynchronous transfer mode networks
    (1997) Albrecht, Frederick Mark; Ventura, M J E
    The aim of this thesis was to design a fuzzy logic controller that could be used to prevent congestion in Asynchronous Transfer Mode networks. The controller would be located at the User-Network Interface of the network and would be used to monitor the incoming traffic. The control action would be to allow conforming traffic through to the network unmodified, while tagging or dropping non-conforming traffic. Three fuzzy logic controllers are presented, the latter two being improvements on design(s) that preceded it. All three controllers are designed to police the sustainable cell rate of Variable Bit Rate (VBR) traffic sources, and take the Sustainable Cell Rate and Peak Cell Rate as input Parameters. The first two controllers require an additional parameter called the Burst Threshold, while the third controller takes the Initial Burst Size as its third traffic parameter. The controllers then continuously analyse the state of the traffic by applying a set of rules that it was given and decides whether the source is conforming or non-conforming, taking corrective action if required. The first controller included two buffers that were used to determine the state of the connection. It was however found that it would be too difficult to determine what sizes to make those buffers, and therefore that design was abandoned in favour of the second controller. The second controller eliminated the need for buffers in the design, while still being able to tag or drop non-conforming cells and allowing conforming cells through unmodified. This was done by including a token leaky bucket in the design and modifying the fuzzy sets and rule base of the fuzzy logic engine accordingly. A