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Nigel Thomas - One of the best experts on this subject based on the ideXlab platform.

  • semi product form solution for pepa models with functional rates
    Analytical and Stochastic Modeling Techniques and Applications, 2013
    Co-Authors: Nigel Thomas, Peter G. Harrison
    Abstract:

    We consider the problem of finding a separable solution for the equilibrium state probabilities in a Markovian Process algebra model, in which the action rates may depend on the behaviour of other components. To do this we consider regular cycles in the underlying state space and show that a semi-product form solution exists when the functions describing the action rates have specific forms. The approach is illustrated with two examples, one a generalised version of a known state-dependent queueing network and the other in the domain of security protocols.

  • efficient solutions of a pepa model of a key distribution centre
    Performance Evaluation, 2010
    Co-Authors: Yishi Zhao, Nigel Thomas
    Abstract:

    In this paper we explore the trade-off between security and performance in considering a model of a key distribution centre. The model is specified using the Markovian Process algebra PEPA. The basic model suffers from the commonly encountered state space explosion problem, and so we apply some efficient techniques to solve it. First, we use model reduction techniques and approximation to give a form of the model (in fact, a closed queueing network model) which is more scalable. We then consider the use of a fluid flow approximation based on ordinary differential equations (ODEs) derived from an alternative form of the simplified model. Finally, we evaluate a utility function of this secure key exchange model. Three questions have been proposed; how many clients can a given KDC configure support? how much service capacity must we provide at a KDC to satisfy a given number of clients? and what is the maximum rate at which keys can be refreshed before the KDC performance begins to degrade under a given demand on a given system? These questions are explored through numerical examples.

  • comparing methods for the efficient analysis of pepa models of non repudiation protocols
    International Conference on Parallel and Distributed Systems, 2009
    Co-Authors: Yishi Zhao, Nigel Thomas
    Abstract:

    In this paper we study the overhead introduced by secure functions in considering two models of non-repudiation protocols. The models are specified using the Markovian Process algebra PEPA. The basic model suffers from the well known state space explosion problem when tackled using Markov chain analysis. Following previous study of performance modelling on security protocols, mean value analysis and fluid flow approximation based on ordinary differential equations (ODEs) have been chosen as efficient analysis techniques. Mean value analysis is an efficient exact method for deriving a limited set of metrics for large numbers of clients involved in the protocols. Fluid flow approximations can be adopted to solve the system with extremely large populations and potentially derive a wider range of metrics. The models are analyzed numerically and results derived from mean value analysis are compared with the ODE solution.

  • mean value analysis for a class of pepa models
    EPEW '09 Proceedings of the 6th European Performance Engineering Workshop on Computer Performance Engineering, 2009
    Co-Authors: Nigel Thomas, Yishi Zhao
    Abstract:

    In this paper a class of closed queueing network is modelled in the Markovian Process algebra PEPA and solved using the classical Mean Value Analysis (MVA). This approach is attractive as it negates the need to derive the entire state space, and so certain metrics from large models can be obtained with little computational effort. The class of model considered includes models which are not obviously classical closed queueing models. The approach is illustrated with three examples.

  • approximate solution of a pepa model of a key distribution centre
    SPEC International Performance Evaluation Workshop, 2008
    Co-Authors: Yishi Zhao, Nigel Thomas
    Abstract:

    In this paper we explore the trade-off between security and performance in considering a model of a key distribution centre. The model is specified using the Markovian Process algebra PEPA. The basic model suffers from the commonly encountered state space explosion problem, and so we apply some model reduction techniques and approximation to give a form of the model which is more scalable. The system is analysed numerically and results derived from the approximation are compared with simulation.

Toshiharu Hasegawa - One of the best experts on this subject based on the ideXlab platform.

  • cell loss and output Process analyses of a finite buffer discrete time atm queueing system with correlated arrivals
    IEEE Transactions on Communications, 1995
    Co-Authors: Tetsuya Takine, Tatsuya Suda, Toshiharu Hasegawa
    Abstract:

    This paper analyzes an ATM switching node with correlated cell arrivals. An ATM switching node is modeled as a discrete-time finite-buffer queue. Cells arrive according to a semi-Markovian Process, where the number of cell arrivals in a given slot depends on the state of the underlying (M-state) Markov chain in both the given slot and the previous slot. This paper presents analysis for various cell loss characteristics such as cell loss probability, the consecutive loss probability, and the distribution of loss period lengths. It also obtains characteristics of the cell output Process from an ATM switching node including the joint distribution of successive cell interdeparture times, and the distributions of busy and idle periods of the cell output Process. It is shown through numerical examples that both the correlation and the variation of cell arrivals significantly affect the cell loss and the output Process characteristics. >

  • cell loss and output Process analyses of a finite buffer discrete time atm queueing system with correlated arrivals
    International Conference on Computer Communications, 1993
    Co-Authors: Tetsuya Takine, Tatsuya Suda, Toshiharu Hasegawa
    Abstract:

    The performance of an asynchronous transfer mode (ATM) switching node is analyzed, taking cell arrival correlation into consideration. An ATM switching node is modeled as a discrete-time finite-buffer queue. Cell arrivals are assumed to follow a semi Markovian Process. Various characteristics of the cell loss and the distribution function of the cell output Process from an ATM switching node are analyzed. The cell loss probability, the consecutive loss probability, the distribution of loss period lengths, the joint distribution of successive cell interdeparture times, and the distributions of busy and idle periods are determined. It is shown that both the correlation and the variation of cell arrivals significantly affect the cell loss and the output Process characteristics. >

Tetsuya Takine - One of the best experts on this subject based on the ideXlab platform.

  • cell loss and output Process analyses of a finite buffer discrete time atm queueing system with correlated arrivals
    IEEE Transactions on Communications, 1995
    Co-Authors: Tetsuya Takine, Tatsuya Suda, Toshiharu Hasegawa
    Abstract:

    This paper analyzes an ATM switching node with correlated cell arrivals. An ATM switching node is modeled as a discrete-time finite-buffer queue. Cells arrive according to a semi-Markovian Process, where the number of cell arrivals in a given slot depends on the state of the underlying (M-state) Markov chain in both the given slot and the previous slot. This paper presents analysis for various cell loss characteristics such as cell loss probability, the consecutive loss probability, and the distribution of loss period lengths. It also obtains characteristics of the cell output Process from an ATM switching node including the joint distribution of successive cell interdeparture times, and the distributions of busy and idle periods of the cell output Process. It is shown through numerical examples that both the correlation and the variation of cell arrivals significantly affect the cell loss and the output Process characteristics. >

  • cell loss and output Process analyses of a finite buffer discrete time atm queueing system with correlated arrivals
    International Conference on Computer Communications, 1993
    Co-Authors: Tetsuya Takine, Tatsuya Suda, Toshiharu Hasegawa
    Abstract:

    The performance of an asynchronous transfer mode (ATM) switching node is analyzed, taking cell arrival correlation into consideration. An ATM switching node is modeled as a discrete-time finite-buffer queue. Cell arrivals are assumed to follow a semi Markovian Process. Various characteristics of the cell loss and the distribution function of the cell output Process from an ATM switching node are analyzed. The cell loss probability, the consecutive loss probability, the distribution of loss period lengths, the joint distribution of successive cell interdeparture times, and the distributions of busy and idle periods are determined. It is shown that both the correlation and the variation of cell arrivals significantly affect the cell loss and the output Process characteristics. >

K L Sebastian - One of the best experts on this subject based on the ideXlab platform.

  • a lower bound to the survival probability and an approximate first passage time distribution for Markovian and non Markovian dynamics in phase space
    Journal of Chemical Physics, 2009
    Co-Authors: Rajarshi Chakrabarti, K L Sebastian
    Abstract:

    We derive a very general expression of the survival probability and the first passage time distribution for a particle executing Brownian motion in full phase space with an absorbing boundary condition at a point in the position space, which is valid irrespective of the statistical nature of the dynamics. The expression, together with the Jensen's inequality, naturally leads to a lower bound to the actual survival probability and an approximate first passage time distribution. These are expressed in terms of the position-position, velocity-velocity, and position-velocity variances. Knowledge of these variances enables one to compute a lower bound to the survival probability and consequently the first passage distribution function. As examples, we compute these for a Gaussian Markovian Process and, in the case of non-Markovian Process, with an exponentially decaying friction kernel and also with a power law friction kernel. Our analysis shows that the survival probability decays exponentially at the long time irrespective of the nature of the dynamics with an exponent equal to the transition state rate constant.

Tatsuya Suda - One of the best experts on this subject based on the ideXlab platform.

  • cell loss and output Process analyses of a finite buffer discrete time atm queueing system with correlated arrivals
    IEEE Transactions on Communications, 1995
    Co-Authors: Tetsuya Takine, Tatsuya Suda, Toshiharu Hasegawa
    Abstract:

    This paper analyzes an ATM switching node with correlated cell arrivals. An ATM switching node is modeled as a discrete-time finite-buffer queue. Cells arrive according to a semi-Markovian Process, where the number of cell arrivals in a given slot depends on the state of the underlying (M-state) Markov chain in both the given slot and the previous slot. This paper presents analysis for various cell loss characteristics such as cell loss probability, the consecutive loss probability, and the distribution of loss period lengths. It also obtains characteristics of the cell output Process from an ATM switching node including the joint distribution of successive cell interdeparture times, and the distributions of busy and idle periods of the cell output Process. It is shown through numerical examples that both the correlation and the variation of cell arrivals significantly affect the cell loss and the output Process characteristics. >

  • cell loss and output Process analyses of a finite buffer discrete time atm queueing system with correlated arrivals
    International Conference on Computer Communications, 1993
    Co-Authors: Tetsuya Takine, Tatsuya Suda, Toshiharu Hasegawa
    Abstract:

    The performance of an asynchronous transfer mode (ATM) switching node is analyzed, taking cell arrival correlation into consideration. An ATM switching node is modeled as a discrete-time finite-buffer queue. Cell arrivals are assumed to follow a semi Markovian Process. Various characteristics of the cell loss and the distribution function of the cell output Process from an ATM switching node are analyzed. The cell loss probability, the consecutive loss probability, the distribution of loss period lengths, the joint distribution of successive cell interdeparture times, and the distributions of busy and idle periods are determined. It is shown that both the correlation and the variation of cell arrivals significantly affect the cell loss and the output Process characteristics. >