26 research outputs found

    A formalism for describing and simulating systems with interacting components.

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    This thesis addresses the problem of descriptive complexity presented by systems involving a high number of interacting components. It investigates the evaluation measure of performability and its application to such systems. A new description and simulation language, ICE and it's application to performability modelling is presented. ICE (Interacting ComponEnts) is based upon an earlier description language which was first proposed for defining reliability problems. ICE is declarative in style and has a limited number of keywords. The ethos in the development of the language has been to provide an intuitive formalism with a powerful descriptive space. The full syntax of the language is presented with discussion as to its philosophy. The implementation of a discrete event simulator using an ICE interface is described, with use being made of examples to illustrate the functionality of the code and the semantics of the language. Random numbers are used to provide the required stochastic behaviour within the simulator. The behaviour of an industry standard generator within the simulator and different methods of number allocation are shown. A new generator is proposed that is a development of a fast hardware shift register generator and is demonstrated to possess good statistical properties and operational speed. For the purpose of providing a rigorous description of the language and clarification of its semantics, a computational model is developed using the formalism of extended coloured Petri nets. This model also gives an indication of the language's descriptive power relative to that of a recognised and well developed technique. Some recognised temporal and structural problems of system event modelling are identified. and ICE solutions given. The growing research area of ATM communication networks is introduced and a sophisticated top down model of an ATM switch presented. This model is simulated and interesting results are given. A generic ICE framework for performability modelling is developed and demonstrated. This is considered as a positive contribution to the general field of performability research

    Matrix-geometric solution of infinite stochastic Petri nets

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    We characterize a class of stochastic Petri nets that can be solved using matrix geometric techniques. Advantages of such on approach are that very efficient mathematical technique become available for practical usage, as well as that the problem of large state spaces can be circumvented. We first characterize the class of stochastic Petri nets of interest by formally defining a number of constraints that have to be fulfilled. We then discuss the matrix geometric solution technique that can be employed and present some boundary conditions on tool support. We illustrate the practical usage of the class of stochastic Petri nets with two examples: a queueing system with delayed service and a model of connection management in ATM network

    Optical Networks for Future Internet Design

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    Performance requirements verification during software systems development

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    Requirements verification refers to the assurance that the implemented system reflects the specified requirements. Requirement verification is a process that continues through the life cycle of the software system. When the software crisis hit in 1960, a great deal of attention was placed on the verification of functional requirements, which were considered to be of crucial importance. Over the last decade, researchers have addressed the importance of integrating non-functional requirement in the verification process. An important non-functional requirement for software is performance. Performance requirement verification is known as Software Performance Evaluation. This thesis will look at performance evaluation of software systems. The performance evaluation of software systems is a hugely valuable task, especially in the early stages of a software project development. Many methods for integrating performance analysis into the software development process have been proposed. These methodologies work by utilising the software architectural models known in the software engineering field by transforming these into performance models, which can be analysed to gain the expected performance characteristics of the projected system. This thesis aims to bridge the knowledge gap between performance and software engineering domains by introducing semi-automated transformation methodologies. These are designed to be generic in order for them to be integrated into any software engineering development process. The goal of these methodologies is to provide performance related design guidance during the system development. This thesis introduces two model transformation methodologies. These are the improved state marking methodology and the UML-EQN methodology. It will also introduce the UML-JMT tool which was built to realise the UML-EQN methodology. With the help of automatic design models to performance model algorithms introduced in the UML-EQN methodology, a software engineer with basic knowledge of performance modelling paradigm can conduct a performance study on a software system design. This was proved in a qualitative study where the methodology and the tool deploying this methodology were tested by software engineers with varying levels of background, experience and from different sectors of the software development industry. The study results showed an acceptance for this methodology and the UML-JMT tool. As performance verification is a part of any software engineering methodology, we have to define frame works that would deploy performance requirements validation in the context of software engineering. Agile development paradigm was the result of changes in the overall environment of the IT and business worlds. These techniques are based on iterative development, where requirements, designs and developed programmes evolve continually. At present, the majority of literature discussing the role of requirements engineering in agile development processes seems to indicate that non-functional requirements verification is an unchartered territory. CPASA (Continuous Performance Assessment of Software Architecture) was designed to work in software projects where the performance can be affected by changes in the requirements and matches the main practices of agile modelling and development. The UML-JMT tool was designed to deploy the CPASA Performance evaluation tests

    Fluidization of Petri nets to improve the analysis of Discrete Event Systems

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    Las Redes de Petri (RdP) son un formalismo ampliamente aceptado para el modelado y análisis de Sistemas de Eventos Discretos (SED). Por ejemplo sistemas de manufactura, de logística, de tráfico, redes informáticas, servicios web, redes de comunicación, procesos bioquímicos, etc. Como otros formalismos, las redes de Petri sufren del problema de la ¿explosión de estados¿, en el cual el número de estados crece explosivamente respecto de la carga del sistema, haciendo intratables algunas técnicas de análisis basadas en la enumeración de estados. La fluidificación de las redes de Petri trata de superar este problema, pasando de las RdP discretas (en las que los disparos de las transiciones y los marcados de los lugares son cantidades enteras no negativas) a las RdP continuas (en las que los disparos de las transiciones, y por lo tanto los marcados se definen en los reales). Las RdP continuas disponen de técnicas de análisis más eficientes que las discretas. Sin embargo, como toda relajación, la fluidificación supone el detrimento de la fidelidad, dando lugar a la pérdida de propiedades cualitativas o cuantitativas de la red de Petri original. El objetivo principal de esta tesis es mejorar el proceso de fluidificación de las RdP, obteniendo un formalismo continuo (o al menos parcialmente) que evite el problema de la explosión de estados, mientras aproxime adecuadamente la RdP discreta. Además, esta tesis considera no solo el proceso de fluidificación sino también el formalismo de las RdP continuas en sí mismo, estudiando la complejidad computacional de comprobar algunas propiedades. En primer lugar, se establecen las diferencias que aparecen entre las RdP discretas y continuas, y se proponen algunas transformaciones sobre la red discreta que mejorarán la red continua resultante. En segundo lugar, se examina el proceso de fluidificación de las RdP autónomas (i.e., sin ninguna interpretación temporal), y se establecen ciertas condiciones bajo las cuales la RdP continua preserva determinadas propiedades cualitativas de la RdP discreta: limitación, ausencia de bloqueos, vivacidad, etc. En tercer lugar, se contribuye al estudio de la decidibilidad y la complejidad computacional de algunas propiedades comunes de la RdP continua autónoma. En cuarto lugar, se considera el proceso de fluidificación de las RdP temporizadas. Se proponen algunas técnicas para preservar ciertas propiedades cuantitativas de las RdP discretas estocásticas por las RdP continuas temporizadas. Por último, se propone un nuevo formalismo, en el cual el disparo de las transiciones se adapta a la carga del sistema, combinando disparos discretos y continuos, dando lugar a las Redes de Petri híbridas adaptativas. Las RdP híbridas adaptativas suponen un marco conceptual para la fluidificación parcial o total de las Redes de Petri, que engloba a las redes de Petri discretas, continuas e híbridas. En general, permite preservar propiedades de la RdP original, evitando el problema de la explosión de estados

    Sistema de comunicaciones tierra-tierra mediante anillo de fibra óptica entre emplazamientos de navegación aérea

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    El proyecto que se expondrá a continuación trata de dar solución a los requisitos especificados por el cliente principal, basados en el diseño e instalación de un sistema de comunicaciones mediante fibra óptica entre los distintos emplazamientos de navegación aérea existentes dentro de un aeropuerto. Dentro de un complejo aeroportuario existen distintos emplazamientos que albergan ayudas para navegación aérea, y es imprescindible la comunicación entre todos. Dentro de ellos se encuentra la Torre de Control desde donde se controlan y gestionan todas las operaciones de las aeronaves. También forman parte los diferentes emplazamientos que dan soporte al aterrizaje, despegue y navegación. Se realizará una revisión de todas las tecnologías de comunicaciones existentes, como son las basadas en multiplexación de la frecuencia, tiempo y longitud de onda. También los protocolos de comunicaciones como pueden ser SNMP (Protocolo Simple de Gestión de Red), TCP (Protocolo de Control de Transporte), IP (Protocolo de Internet) y Ethernet. Para dar solución al presente proyecto, se utilizará SDH (Jerarquía Digital Síncrona) como principal tecnología. Sobre SDH se pueden destacar mejoras en la velocidad de transmisión, mayor fiabilidad con mecánicos automáticos de protección ante fallos y gran capacidad de ampliación en el futuro. El diseño y ejecución del proyecto se llevará a cabo cumpliendo unas directrices comunes, que responden a unos estándares de gestión de proyectos, mediante herramientas como el diagrama de tiempos de ejecución del proyecto, normativas de seguridad, informes de seguimiento, etc. Por último, se obtendrán las conclusiones finales técnicas de cara a la mejora en futuros proyectos que se realicen en similares condiciones.This project is a solution to the specified requirements by the primary client, based on the design and installation of a fiber optic communication between different air navigation sites in an airport. Inside an airport there are many sites that have air navigation aids and the communication is essential between them. The Control Tower is the principal site where you can control and manage all aircraft operations. Also includes various sites that support the landing, takeoff and navigation. A revision of the existing communication technologies will be provided, such as those based on frequency, time and wavelength division multiplexing. Also the communications protocols such as SNMP (Simple Network Management Protocol), TCP (Transport Control Protocol), IP (Internet Protocol) and Ethernet. To solve this project, SDH (Synchronous Digital Hierarchy) has been used as the main technology in this project. Regarding SDH, it can be highlighted improvements in transmission speed, higher reliability with automatic mechanical failure protection and highly scalable in the future. Design and implementation will be carried out in compliance with standard guidelines, which meet standards of project management, using tools such as the timing diagram, safety regulations, monitoring reports, etc. Finally, technical conclusions for the enhancement in future project carried out in similar conditions, will be obtained.Ingeniería Técnica en Sistemas de Telecomunicació

    34th Midwest Symposium on Circuits and Systems-Final Program

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    Organized by the Naval Postgraduate School Monterey California. Cosponsored by the IEEE Circuits and Systems Society. Symposium Organizing Committee: General Chairman-Sherif Michael, Technical Program-Roberto Cristi, Publications-Michael Soderstrand, Special Sessions- Charles W. Therrien, Publicity: Jeffrey Burl, Finance: Ralph Hippenstiel, and Local Arrangements: Barbara Cristi
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