Rich Interfaces for Dependability: Compositional Methods for Dynamic Fault Trees and Arcade models

This paper discusses two behavioural interfaces for reliability analysis: dynamic fault trees, which model the system reliability in terms of the reliability of its components and Arcade, which models the system reliability at an architectural level. For both formalisms, the reliability is analyzed by transforming the DFT or Arcade model to a set of input-output Markov Chains. By using compositional aggregation techniques based on weak bisimilarity, significant reductions in the state space can be obtained

Formal support of process chain networks using model-driven engineering and Petri nets

© Owner/Author | ACM 2019. This is the author's version of the work. It is posted here for your personal use. Not for redistribution. The definitive Version of Record was published in SAC: Symposium on Applied Computing, http://dx.doi.org/10.1145/3297280.3299752Poster presentado en 34th ACM/SIGAPP Symposium on Applied Computing celebrado en 2019 en Limassol,CyprusBusiness process modelling is an essential activity for competitive enterprises, as it enables documenting, analysing, improving and automating their core processes. Several notations have been proposed, including BPMN, service blueprints or Process Chain Networks (PCNs). These are all graphical, intuitive notations, which are useful for discussion and documentation, but tool support and a formal semantics are required for process analysis. However, tool support is lacking and formal semantics is not available for some commonly used notations among business people, like PCNs. To alleviate this situation, we present a modelling tool for PCNs, and a formal semantics based on Generalized Stochastic Petri nets, which permits analysis. We have realized our approach using Model-driven Engineering, and show its realization within INNoVaServ, a modeling environment for the design of business models and service process operations.Work supported by Spanish MINECO (TIN2014-52129-R) and the region of Madrid (S2013/ICE-3006 and P2018/TCS-4314

An efficient algorithm for the parallel solution of high-dimensional differential equations

The study of high-dimensional differential equations is challenging and difficult due to the analytical and computational intractability. Here, we improve the speed of waveform relaxation (WR), a method to simulate high-dimensional differential-algebraic equations. This new method termed adaptive waveform relaxation (AWR) is tested on a communication network example. Further we propose different heuristics for computing graph partitions tailored to adaptive waveform relaxation. We find that AWR coupled with appropriate graph partitioning methods provides a speedup by a factor between 3 and 16

Evaluation of a benchmark on dynamic reliability via Fluid Stochastic Petri Nets

The paper presents the evaluation of a benchmark on dynamic reliability. Such system consists of a tank containing some liquid, two pumps and one valve to renew the liquid in the tank, a heat source warming the liquid, and a controller acting on the state of the components. Three failure conditions are possible: the dry out, the over\ufb02ow or the high temperature of the liquid. Due to the presence of continuous variables, such as the liquid level and temperature, the system is modelled as a Fluid Stochastic Petri Net which is the object of simulation obtaining the unreliability evaluation of the system

On Zone-Based Analysis of Duration Probabilistic Automata

We propose an extension of the zone-based algorithmics for analyzing timed automata to handle systems where timing uncertainty is considered as probabilistic rather than set-theoretic. We study duration probabilistic automata (DPA), expressing multiple parallel processes admitting memoryfull continuously-distributed durations. For this model we develop an extension of the zone-based forward reachability algorithm whose successor operator is a density transformer, thus providing a solution to verification and performance evaluation problems concerning acyclic DPA (or the bounded-horizon behavior of cyclic DPA).Comment: In Proceedings INFINITY 2010, arXiv:1010.611

NaMANET – Nagy kiterjedésű mobil ad hoc hálózatok vizsgálata = NaMANET - Investigation of Large-Scale Mobile Ad Hoc Networks

A NaMANET projekt keretében elsősorban a nagy kiterjedésű mobil ad hoc hálózatok, valamint a vezeték nélküli közösségi hálózatok témájával foglalkoztunk. A mobil ad hoc hálózatok közvetlen adatátvitelt biztosító kommunikációs megoldásokra épülő lokális hálózatok, míg a vezeték nélküli közösségi hálózatok ideális körülményeket nyújthatnak ad hoc alkalmazások implementálására és bevezetésére mintegy összekötő gerinchálózatot biztosítva a mobil ad hoc hálózati szigetek számára. Kutatásaink során modelleztük és szimulációk segítségével vizsgáltuk az alkalmazásterjedést nagy kiterjedésű ad hoc hálózatokban. Összehasonlítottuk különböző szolgáltatásmenedzsment architektúrák teljesítőképességét. Megvizsgáltuk különböző információterjesztési stratégiák hatékonyságát járművek alkotta ad hoc hálózatokban, valamint megvizsgáltunk különböző klaszterezési eljárásokat biztonság és megbízhatóság szempontjából szenzor hálózatokban. Foglalkoztunk okostelefonok ad hoc hálózatokban való használatával. Terveztünk és implementáltunk egy szolgáltatástámogatási keretrendszert demo alkalmazásokkal, valamint megvizsgáltuk az ad hoc hálózatok alkalmazhatóságának kérdéskörét beltéri navigációs rendszer esetén. Foglalkoztunk vezeték nélküli közösségi hálózatok tervezési, kiépítési, üzemeltetési kérdéseivel, továbbá kidolgoztunk egy link állapotváltozást előrejelző eljárást vezeték nélküli hálózatokra. Eredményeinket számos nemzetközi konferenciacikk, folyóiratcikk és könyvfejezet formájában publikáltuk. | In the NaMANET project, we mainly focused on the investigation of large-scale mobile ad hoc networks, and the field of wireless community networks. In mobile ad hoc networks, the mobile nodes close to each other can communicate directly with their neighbors, since wireless community networks can provide ideal conditions as a backbone of the ad hoc network islands for implementing and deploying ad hoc applications. In our research, we modeled and via simulations investigated application spreading in large-scale ad hoc networks. We compared the performance of different service management architectures. We investigated the efficiency of different message spreading strategies in vehicular ad hoc networks, moreover surveyed and analysed clustering algorithms and protocols used in sensor networks from the viewpoint of security and reliability. We also dealt with using smartphones in ad hoc networks. We developed and implemented a service provisioning framework for ad hoc networks together with some demo applications, and investigated the usability of ad hoc networks in indoor navigation. Furthermore, we dealt with the area of developing, deploying and maintaining wireless community networks, and developed a link state prediction algorithm for wireless networks. We published our results in several international conference papers, journal papers and book chapters

Construction and Verification of Performance and Reliability Models

Over the last two decades formal methods have been extended towards performance and reliability evaluation. This paper tries to provide a rather intuitive explanation of the basic concepts and features in this area. Instead of striving for mathematical rigour, the intention is to give an illustrative introduction to the basics of stochastic models, to stochastic modelling using process algebra, and to model checking as a technique to analyse stochastic models

Programmable models of growth and mutation of cancer-cell populations

In this paper we propose a systematic approach to construct mathematical models describing populations of cancer-cells at different stages of disease development. The methodology we propose is based on stochastic Concurrent Constraint Programming, a flexible stochastic modelling language. The methodology is tested on (and partially motivated by) the study of prostate cancer. In particular, we prove how our method is suitable to systematically reconstruct different mathematical models of prostate cancer growth - together with interactions with different kinds of hormone therapy - at different levels of refinement.Comment: In Proceedings CompMod 2011, arXiv:1109.104

Erlang analysis of cellular networks using stochastic Petri nets and user-in-the-loop extension for demand control

Abstract—Cellular networks face severe challenges due to the expected growth of application data rate demand with an increase rate of 100 % per year. Over-provisioning capacity has been the standard approach to reduce the risk of overload situations. Traditionally in telephony networks, call blocking and overload probability have been analyzed using the Erlang-B and Erlang-C formulas, which model limited capacity communication systems without or with session request buffers, respectively. While a closed-form expression exists for the blocking probability for constant load and service, a steady-state Markov chain (MC) analysis can always provide more detailed data, as long as the Markov property of the arrival and service processes hold. However, there is a significant modeling advantage by using the stochastic Petri net (SPN) paradigm to model the details of such a system. In addition, software tool support allows getting numeric analysis results quickly by solving the state probabilities in the background and without the need to run any simulation. Because of this efficiency, the equivalent SPN model of the Engset, Erlang-B and Erlang-C situation is introduced as novelty in this paper. Going beyond the original Erlang scenario, the user-in-the-loop (UIL) approach of demand shaping by closed-loop control is studied as an extension. In UIL, demand control is implemented by a dynamic usage-based tariff which motivates users to reduce or postpone the use of applications on their smart phone in times of light to severe congestion. In this paper, the effect of load on the price and demand reduction is modeled with an SPN based on the classical Erlang Markov chain structure. Numeric results are easily obtained and presented in this paper, including probability density functions (PDF) of the load situation, and a parameter analysis showing the effectiveness of UIL to reduce the overload probability. Keywords—User-in-the-loop (UIL); demand shaping; demand control; congestion; Erlang; stochastic Petri-net (SPN). I