Simulation and analysis of adaptive routing and flow control in wide area communication networks

This thesis presents the development of new simulation and analytic models for the performance analysis of wide area communication networks. The models are used to analyse adaptive routing and flow control in fully connected circuit switched and sparsely connected packet switched networks. In particular the performance of routing algorithms derived from the L(_R-I) linear learning automata model are assessed for both types of network. A novel architecture using the INMOS Transputer is constructed for simulation of both circuit and packet switched networks in a loosely coupled multi- microprocessor environment. The network topology is mapped onto an identically configured array of processing centres to overcome the processing bottleneck of conventional Von Neumann architecture machines. Previous analytic work in circuit switched work is extended to include both asymmetrical networks and adaptive routing policies. In the analysis of packet switched networks analytic models of adaptive routing and flow control are integrated to produce a powerful, integrated environment for performance analysis The work concludes that routing algorithms based on linear learning automata have significant potential in both fully connected circuit switched networks and sparsely connected packet switched networks

Parallel simulation techniques for telecommunication network modelling

In this thesis, we consider the application of parallel simulation to the performance modelling of telecommunication networks. A largely automated approach was first explored using a parallelizing compiler to speed up the simulation of simple models of circuit-switched networks. This yielded reasonable results for relatively little effort compared with other approaches. However, more complex simulation models of packet- and cell-based telecommunication networks, requiring the use of discrete event techniques, need an alternative approach. A critical review of parallel discrete event simulation indicated that a distributed model components approach using conservative or optimistic synchronization would be worth exploring. Experiments were therefore conducted using simulation models of queuing networks and Asynchronous Transfer Mode (ATM) networks to explore the potential speed-up possible using this approach. Specifically, it is shown that these techniques can be used successfully to speed-up the execution of useful telecommunication network simulations. A detailed investigation has demonstrated that conservative synchronization performs very well for applications with good look ahead properties and sufficient message traffic density and, given such properties, will significantly outperform optimistic synchronization. Optimistic synchronization, however, gives reasonable speed-up for models with a wider range of such properties and can be optimized for speed-up and memory usage at run time. Thus, it is confirmed as being more generally applicable particularly as model development is somewhat easier than for conservative synchronization. This has to be balanced against the more difficult task of developing and debugging an optimistic synchronization kernel and the application models

Autonomy in the real real-world: A behaviour based view of autonomous systems control in an industrial product inspection system

The thesis presented in this dissertation appears in two sequential parts that arose from an exploration of the use of Behaviour Based Artificial Intelligence (BBAI) techniques in a domain outside that of robotics, where BBAI is most frequently used. The work details a real-world physical implementation of the control and interactions of an industrial product inspection system from a BBAI perspective. It concentrates particularly on the control of a number of active laser scanning sensor systems (each a subsystem of a larger main inspection system), using a subsumption architecture. This industrial implementation is in itself a new direction for BBAI control and an important aspect of this thesis. However, the work has also led on to the development of a number of key ideas which contribute to the field of BBAI in general. The second part of the thesis concerns the nature of physical and temporal constraints on a distributed control system and the desirability of utilising mechanisms to provide continuous, low-level learning and adaptation of domain knowledge on a sub-behavioural basis. Techniques used include artificial neural networks and hill-climbing state-space search algorithms. Discussion is supported with examples from experiments with the laser scanning inspection system. Encouraging results suggest that concerted design effort at this low level of activity will benefit the whole system in terms of behavioural robustness and reliability. Relevant aspects of the design process that should be of value in similar real-world projects are identified and emphasised. These issues are particularly important in providing a firm foundation for artificial intelligence based control systems

Viper : a visualisation tool for parallel program construction

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Interactive Analysis of Large Distributed Systems with Topology-based Visualization

The performance of parallel and distributed applications is highly dependent on the characteristics of the execution environment. In such environments, the network topology and characteristics directly impact data locality and movements as well as contention, which are key phenomena to understand the behavior of such applications and possibly improve it. Unfortunately few visualization available to the analyst are capable of accounting for such phenomena. In this paper, we propose an interactive topology-based visualization technique based on data aggregation that enables to correlate network characteristics, such as bandwidth and topology, with application performance traces. We claim that such kind of visualization enables to explore and understand non trivial behavior that are impossible to grasp with classical visualization techniques. We also claim that the combination of multi-scale aggregation and dynamic graph layout allows our visualization technique to scale seamlessly to large distributed systems. We support these claims through a detailed analysis of a high performance computing scenario and of a grid computing scenario.Les performances des applications parallèles et distribuées dépendent fortement des caractéristiques de l'environnement d'exécution. Dans de tels environnements, la topologie du réseau et ses caractéristiques ont un impact direct sur la localité et les mouvements des données ainsi que sur la contention, qui sont des phénomènes clés pour comprendre le comportement de ces applications et éventuellement les améliorer. Malheureusement, peu de visualisation permettent de mettre en évidence ces phénomènes. Dans cet article, nous proposons une technique de visualisation interactive et topologique basée sur l'agrégation de données qui permet de corréler les caractéristiques du réseau, telles que la bande passante et la topologie, avec des traces de performances des applications. Ce type de visualisation permet d'explorer et de comprendre des comportements non triviaux qui sont impossibles à appréhender avec les techniques de visualisation classiques. Nous affirmons également que la combinaison de l'agrégation multi-échelle et l'agencement dynamique du graphe permet à notre technique de visualisation de passer à l'échelle. Nous étayons ces affirmations par l'analyse détaillée d'un scénario de calcul haute performance et d'un scénario de grid computing

Lewis Structures Technology, 1988. Volume 1: Structural Dynamics

The specific purpose of the symposium was to familiarize the engineering structures community with the depth and range of research performed by the Structures Division of the Lewis Research Center and its academic and industrial partners. Sessions covered vibration control, fracture mechanics, ceramic component reliability, parallel computing, nondestructive testing, dynamical systems, fatigue and damage, wind turbines, hot section technology, structural mechanics codes, computational methods for dynamics, structural optimization, and applications of structural dynamics

Interrupt-generating active data objects

An investigation is presented into an interrupt-generating object model which is designed to reduce the effort of programming distributed memory multicomputer networks. The object model is aimed at the natural modelling of problem domains in which a number of concurrent entities interrupt one another as they lay claim to shared resources. The proposed computational model provides for the safe encapsulation of shared data, and incorporates inherent arbitration for simultaneous access to the data. It supplies a predicate triggering mechanism for use in conditional synchronization and as an alternative mechanism to polling. Linguistic support for the proposal requires a novel form of control structure which is able to interface sensibly with interrupt-generating active data objects. The thesis presents the proposal as an elemental language structure, with axiomatic guarantees which enforce safety properties and aid in program proving. The established theory of CSP is used to reason about the object model and its interface. An overview is presented of a programming language called HUL, whose semantics reflect the proposed computational model. Using the syntax of HUL, the application of the interrupt-generating active data object is illustrated. A range of standard concurrent problems is presented to demonstrate the properties of the interrupt-generating computational model. Furthermore, the thesis discusses implementation considerations which enable the model to be mapped precisely onto multicomputer networks, and which sustain the abstract programming level provided by the interrupt-generating active data object in the wider programming structures of HUL