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No description available.

The Internet and associated network technologies are an increasingly integral part of modem day working practices. With this increase in use comes an increase in dependence. For some time commentators have noted that given the level of reliance on data networks, there is a paucity of monitoring tools and techniques to support them. As this area is addressed, more data regarding network perfonnance becomes available. However, a need to automatically analyse and interpret this perfonnance data now becomes imperative. This thesis takes one-way latency as an example perfonnance metric. The tenn 'Data Exception' is then employed to describe delay data that is unusual or unexpected due to some fundamental change in the underlying network perfonnance. Data Exceptions can be used to assess the effect of network modifications and failures and can also help in the diagnosis of network faults and perfonnance trends. The thesis outlines how Data Exceptions can be identified by the use of a two-stage approach. The Kolmogorov-Smirnov test can initially be applied to detect general changes in the delay distribution, and where such a change has taken place, a neural network can then be used to categorise the change. This approach is evaluated using both a network simulation and a test network to generate a range of delay Data Exceptions.

This thesis makes a contribution towards cutting the cost of development of real-time systems, The development of real-time systems is difficult: often errors in the specification are not identified until late in the development pro- cess, and there is a requirment to reduce the amount of rework to correct flaws introduced in the early stages of development, A Real-time network- Specification Language (RTN-SL) is being developed to allow the rigorous specification of functionality and timing properties of computations, The correct specification of end to end timing constraints, however requires an understanding of the timing properties of the communication between components. A theory of communication is therefore required to be used with the RTN-SL, to analyse timing properties of systems early in the development process. The work demonstrates how a tool set can be used to gain an under- standing of the behaviour of the system, to help to identify and correct ambiguities that arise in the early stages of development. An incremental development approach is recommended, Starting with an abstract model and exploring properties of increasingly realistic models of the implementa- tion, to gain confidence about the correctness of the implementation and an understanding of its behaviour, The strengths and weaknesses of a number of tools are discussed and it is shown that it is possibk to use a compositional rely-guaranteed method to verify properties of systems where the individual components give few or no guarantees about their behaviour. This rely guar- antee method makes it possible to record assumptions in the specification, to help ensure they are not overlooked and thereby introduce errors in the design and implementation, This approach can form the basis of a theory of communication, which can be used with the RTN-SL to reason about end to end timing properties of systems in the early stages of development.

In the context ofFixed-Priority Scheduling in Real-Time Systems, we investigate scheduling mechanisms for supporting systems where, in addition to timing constraints, their performance with respect to additional QoS requirements must be improved. This'type of situation may occur when the worst-case res~urce requirements of all or some running tasks cannot be simultaneously met due to task contention. . Solutions to these problems have been proposed in the context of both fixed-priority and dynamic-priority scheduling. In fixed-priority scheduling, the typical approach is to artificially modify the attributes or structure of tasks, and/or usually require non-standard run-time support. In dynamic-priority scheduling approaches, utility functions are employed to make scheduling decisions with the objective of maximising the utility. The main difficulties with these approaches are the inability to formulate and model appropriately utility functions for each task, and the inability to guarantee hard deadlines without executing computationally costly algorithms. In this thesis we propose a different approach. Firstly, we introduce the concept of relative importance among tasks as a new metric for expressing QoS requirements. The meaning of this importance relationship is to express that in a schedule it i~ desirable to run a task in preference to other ones. This model is more intuitive and less restrictive than traditional utility-based app~oaches. Secondly, we formulate a scheduling problem in terms of finding a feasible assignment of fixed priorities that maximises the new QoS metric, and propose the DI and DI+ algorithms that find optimal solutions. By extensive simulation, we show that the new QoS metric combined with the DI algorithm outperforms the rate monotonic priority algorithm in several practical problems such as minimising jitter, minimising the number of preemptions or minimising the latency. In addition, our approach outperforms EDF in several scenarios.

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The Consumer Electronics industry produces a large number of systems which exhibit both real-time and embedded properties (RTES). Frequently problems are encountered during the development of these systems due to a mismatch between the requirements of traditional real-time development techniques and the restrictions imposed on the development process by the retail market. There is therefore a requirement for a method which can be used to enhance the development process and improve the reliability of these systems, yet which does not require the intensive formal analysis often required by established real-time development techniques. Observing that organisms in the natural world often exhibit characteristics which would be desirable in computer systems, such as the ability to adapt to changing environments and protect themselves against attack from external agents, this thesis examines the potential for techniques inspired by biological observations to be employed as a means to detect common problems encountered in the development of RTES. The Dendritic Cell Algorithm (DCA), an algorithm derived from the observed operation of the innate immune system which has previously been applied to a number of anomaly-detection problems, is included in a simulated RTES to detect deadline overruns in a task scheduling system, and its effectiveness investigated over a variety of sample systems of varying sizes and complexities. In conjunction with this, the issues surrounding the incorporation of an immune-inspired technique into embedded systems are examined in detail, with focus on the optimisation of the DCA for maximum effectiveness, whilst still providing flexibility. Attention is paid towards ensuring that the DCA is able to function satisfactorily in a constrained environment, by establishing the level of system resources required and proposing further enhancements to the algorithm to enhance its suitability for constrained-resource implementation. The work makes contributions to the real-time community by proposing an original method by which software development for real-time embedded systems can be enhanced, to enable the production of reliable software without the need for the formal analysis procedures normally needed. There are also significant contributions made to the AIS community, by way of the introduction of an application domain in which the application of AIS techniques has not previously been proposed, and the enhancements made to the DCA to make it better suited to this domain than previously.

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