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Quantitative Evaluation of Systems, 2005. Second International Conference on the

Date 19-22 Sept. 2005

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  • Second International Conference on the Quantitative Evaluation of Systems [front matter]

    Page(s): c1 - c11
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  • Proceedings. Second International Conference on the Quantitative Evaluation of Systems

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  • Second International Conference on the Quantitative Evaluation of Systems - Copyright

    Page(s): iv - ivv
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  • Second International Conference on the Quantitative Evaluation of Systems - Table of contents

    Page(s): iv - ivv
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  • Message from the General Chair

    Page(s): ix - ixx
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  • Message from the Program Chairs

    Page(s): x
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  • Organizers

    Page(s): xii - xiii
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  • Technical Program Committee

    Page(s): xiii - xiiii
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  • list-reviewer

    Page(s): xiv - xivv
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  • Formal executable descriptions of biological systems

    Page(s): 2 - 11
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (344 KB) |  | HTML iconHTML  

    The similarities between systems of living entities and systems of concurrent processes may support biological experiments in silico. Process calculi offer a formal framework to describe biological systems, as well as to analyse their behaviour, both from a qualitative and a quantitative point of view. A couple of little examples help us in showing how this can be done. We mainly focus our attention on the qualitative and quantitative aspects of the considered biological systems, and briefly illustrate which kinds of analysis are possible. We use a known stochastic calculus for the first example. We then present some statistics collected by repeatedly running the specification, that turn out to agree with those obtained by experiments in vivo. Our second example motivates a richer calculus. Its stochastic extension requires a non trivial machinery to faithfully reflect the real dynamic behaviour of biological systems. View full abstract»

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  • Introducing probability within state class analysis of dense-time-dependent systems

    Page(s): 13 - 22
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (592 KB) |  | HTML iconHTML  

    Several techniques have been proposed for symbolic enumeration and analysis of the state space of reactive systems with nondeterministic temporal parameters taking values within a dense domain. In a large part of these techniques, the state space is covered by collecting states within equivalence classes each comprised of a discrete logical location and a dense variety of clock valuations encoded as a difference bounds matrix (DBM). The reachability relation among such classes enables qualitative verification of properties pertaining the ordering of events along critical runs and the satisfaction of stimulus/response deadlines. However, up to now, no results have been proposed which extend state class enumeration so as to combine the verification of the possibility of critical behaviors with a quantitative evaluation of their probability. In this paper, we extend the concept of equivalence classes based on DBM encoding with a density function which provides a measure for the probability associated with individual states collected in the class itself. To this end, we extend the formalism of time Petri nets by associating the static firing interval of each transition with a probability density function. We then expound how this probabilistic information determines a probability for the states collected within a class and how this probability evolves in the enumeration of the reachability relation among state classes. This opens the way to characterizing the possibility of critical behaviors with a quantitative measure of probability. View full abstract»

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  • On the use of exact lumpability in partially symmetrical well-formed nets

    Page(s): 23 - 32
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (336 KB) |  | HTML iconHTML  

    Well-formed nets (WNs) have proved an efficient model for building quotient reachability graphs that can be used either for qualitative or performance analysis. However, local asymmetries often break any possibility of grouping states into classes, thus drastically reducing the interest of the approach. An efficient solution has been proposed for qualitative analysis, which relies on a separate representation of the asymmetries in a so called control automaton. The quotient graph is then obtained by synchronizing the transitions of the WN model with the transitions of the control automaton. In this paper, we improve this approach to quantitative analysis. We show that it can be used to build an aggregated graph that is isomorphic to a Markov chain which verifies exact lumpability. Theoretical considerations and practical experiments show that our method outperforms previous approaches. View full abstract»

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  • Fluid flow approximation of PEPA models

    Page(s): 33 - 42
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (352 KB) |  | HTML iconHTML  

    In this paper we present a novel performance analysis technique for large scale systems modelled in the stochastic process algebra PEPA. In contrast to the well-known approach of analysing via continuous time Markov chains, our underlying mathematical representation is a set of coupled ordinary differential equations (ODEs). This analysis process supports all of the comhinators of the PEPA algebra and is well suited to systems with large numbers of replicated components. The paper presents an elegant procedure for the generation of the ODEs and compares the results of this analysis with more conventional methods. View full abstract»

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  • Comparative analysis of bisimulation relations on alternating and non-alternating probabilistic models

    Page(s): 44 - 53
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (344 KB) |  | HTML iconHTML  

    We consider bisimulation and weak bisimulation relations in the context of the labeled Markov chains of Hansson and Jonsson, the concurrent labeled Markov chains of Philippou, Lee, and Sokolsky, and the probabilistic automata of Segala. We identify a taxonomy of bisimulation relations that captures the existing definitions for each one of the three models, and we compare the relations within each model and across models. The comparison across models is given according to a notion of embedding, where we order the three models by generality and we view objects in less general models as objects of more general models. View full abstract»

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  • An approximation algorithm for labelled Markov processes: towards realistic approximation

    Page(s): 54 - 61
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (384 KB) |  | HTML iconHTML  

    Approximation techniques for labelled Markov processes on continuous state spaces were developed by Desharnais, Gupta, Jagadeesan and Panangaden. However, it has not been clear whether this scheme could be used in practice since it involves inverting a stochastic kernel. We describe a Monte Carlo based implementation scheme for this approximation algorithm. This is, to the best of our knowledge, the first implementation of this approximation scheme. The implementation involves some novel ideas about how to estimate infs using sampling and also replacing the explicit description of subsets of the state space by tests for membership. It is hoped that this work enables more applications of continuous probabilistic LMP theory to emerge. View full abstract»

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  • Toward picture-perfect streaming on the Internet

    Page(s): 63 - 72
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (376 KB) |  | HTML iconHTML  

    Quality of service (QoS) in streaming of continuous media over the Internet is poor, which is partly due to variations in delays, bandwidth limitations, and packet losses. Although continuous media applications can tolerate some missing data, non-recoverable information loss degrades these applications' QoS. Consequently, a number of application areas have backed away from streaming of their content over the Internet. Inability to control the resulting visual and auditory quality of the streamed presentation is an important reason for such a trend. We believe that this trend can be reversed. To this end, this paper gives an overview of our efforts in exploring high quality streaming through the exploitation of multiple paths existing in the network. By high quality, we mean with significant bandwidth requirements, of relatively long duration, and without information loss or hiccups in data delivery. We believe this to be a promising approach. View full abstract»

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  • The use of optimal filters to track parameters of performance models

    Page(s): 74 - 83
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (376 KB) |  | HTML iconHTML  

    Autonomic computer systems react to changes in the system, including failures, load changes, and changed user behaviour. Autonomic control may be based on a performance model of the system and the software, which implies that the model should track changes in the system. A substantial theory of optimal tracking filters has a successful history of application to track parameters while integrating data from a variety of sources, an issue which is also relevant in performance modeling. This work applies extended Kalman filtering to track the parameters of a simple queueing network model, in response to a step change in the parameters. The response of the filter is affected by the way performance measurements are taken, and by the observability of the parameters. View full abstract»

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  • Multisolution of complex performability models in the OsMoSys/DrawNET framework

    Page(s): 85 - 94
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (376 KB) |  | HTML iconHTML  

    In the last years some infrastructures and frameworks have been proposed to enable the compositional development of multiformalism models. The OsMoSys/DrawNET framework allows to develop and analyze complex performability models which are composed by several submodels expressed by means of different formal languages. In this paper we describe the approach to multisolution of multiformalism models in the OsMoSys/DrawNET framework and we introduce the mechanisms used to define the performance indices and generate the required results. View full abstract»

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  • Evaluating the dependability of a LEO satellite network for scientific applications

    Page(s): 95 - 104
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (808 KB) |  | HTML iconHTML  

    Dependability is an important issue in LEO satellite networks. In this paper, we study the dependability of a proposed LEO satellite network for scientific data collection based on the Illinois observing nanosatellite (ION). In particular, we first use analytical techniques to determine the amount of radiation shielding and number of redundant components, such as batteries and regulators, needed to achieve particular reliability goals for an individual satellite. We then incorporate the satellite model into a larger satellite network model to analyze network performance and dependability using simulation. Both models are represented as stochastic activity networks (SANs) in Mobius, making it possible to combine them and choose the best solution technique (analytical vs. simulation). Our results show how accumulated radiation dosage affects the functioning of the proposed network, and how redundancy and shielding can be profitably used to increase dependability. View full abstract»

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  • On the performance of D-redundant disk systems

    Page(s): 105 - 112
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (328 KB) |  | HTML iconHTML  

    In this paper we formally introduce the notion of a D-redundant disk system. The class of D-redundant systems includes the class of physically mirrored disks with D copies as well as the more recently introduced SR systems. We provide a very general lower bound on the average access time of any D-redundant system. Using the lower bound we show that that the SR systems of Yu et al. are within 15 percent of optimal performance. We also show how SR systems can be combined with anticipatory head movement policies (AHM) to provide systems which are optimal within 5 percent. View full abstract»

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  • Steady state solution for models with geometric and finite support activity duration

    Page(s): 114 - 123
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (384 KB) |  | HTML iconHTML  

    This paper addresses steady state solution of discrete time stochastic models in which every activity duration is given either by a geometric or a finite support distribution. Finite support distributions can be described by discrete time phase type (DPH) distributions. The behaviour of the whole stochastic model is given by a discrete time Markov chain (DTMC). The DTMC is subject to the so-called state space explosion. We present a technique for obtaining the steady state solution that alleviates this problem. The technique is based on Gaussian elimination combined with an iterative technique. View full abstract»

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  • A MAP fitting approach with independent approximation of the inter-arrival time distribution and the lag correlation

    Page(s): 124 - 133
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (720 KB) |  | HTML iconHTML  

    This paper proposes a two-step Markov arrival process (MAP) fitting approach, where the first step is the phase type fitting of the inter-arrival time and the second step is the approximation of the first n lag correlation values. Depending on the description of the arrival process to approximate various phase type fitting methods can be applied for the first step. In the second step the approximation of the lag correlation values is computed through a non-linear optimization problem. Numerical examples demonstrate the abilities and the limits of the fitting method. View full abstract»

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  • Approximate analysis of stochastic models by self-correcting aggregation

    Page(s): 134 - 143
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (632 KB) |  | HTML iconHTML  

    We present an approximation algorithm for the analysis of large stochastic models. The fixed point iteration approach uses different approximate aggregations of the state space of a model. The stationary state probabilities of these aggregated models are calculated to derive refined aggregations which are used for the correction of the approximate aggregations. The presented method is then extended to benefit from components of higher level model descriptions by defining pairwise overlapping aggregations of the state space of a model. This construction of the aggregated models makes the automatic generation of appropriate aggregations possible, such that the interactions of the submodels are taken into consideration. Together with a well known aggregation formula and new and simple correction formulas the method is easy to implement. The good accuracy of the presented algorithm is shown by means of large examples and the results are compared with the results derived by simulation. View full abstract»

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  • Model checking for survivability!

    Page(s): 145 - 154
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (344 KB) |  | HTML iconHTML  

    Business and social life have become increasingly dependent on large-scale communication and information systems. A partial or complete breakdown as a consequence of natural disasters or purposeful attacks might have severe impacts. Survivability refers to the ability of a system to recover from such disaster circumstances. Evaluating survivability should therefore be an important part of communication system design. In this paper we take a model checking approach toward assessing survivability. We use the logic CSL to phrase survivability in a precise manner. The system operation is modelled through a labelled CTMC. Model checking algorithms can then decide automatically whether the system is survivable. We illustrate our method by evaluating the survivability of the Google file system using stochastic Petri nets. View full abstract»

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  • Checking LTL properties of recursive Markov chains

    Page(s): 155 - 164
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (384 KB) |  | HTML iconHTML  

    We present algorithms for the qualitative and quantitative model checking of linear temporal logic (LTL) properties for recursive Markov chains (RMCs). Recursive Markov chains are a natural abstract model of procedural probabilistic programs and related systems involving recursion and probability. For the qualitative problem ("given a RMC A and an LTL formula φ, do the computations of A satisfy φ almost surely?) we present an algorithm that runs in polynomial space in A and exponential time in φ. For several classes of RMCs, including RMCs with one exit (a special case that corresponds to well-studied probabilistic systems, e.g., multi-type branching processes and stochastic context-free grammars) the algorithm runs in polynomial time in A and exponential time in φ. On the other hand, we also prove that the problem is EXPTIME-hard, and hence it is EXPTlME-complete. For the quantitative problem ("does the probability that a computation of A satisfies φ exceed a given threshold p?", or approximate the probability within a desired precision) we present an algorithm that runs in polynomial space in A and exponential space in φ. For linearly-recursive RMCs, we can compute the exact probability in time polynomial in A and exponential in φ. These results improve by one exponential, in both the qualitative and quantitative case, the complexity that one would obtain if one first translated the LTL formula to a Buchi automaton and then applied the model checking algorithm for Buchi automata from K. Etessami and M. Yannakakis (2005). Our results combine techniques developed in A. Pnueli and L. D. Zuck. (1993) for analysts of RMCs and in C. Courcoubetis and M. Yannakakis (1995) for LTL model checking of flat Markov Chains, and extend them with new techniques. View full abstract»

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