A data type for discretized time representation in DEVS

International audienceThis paper addresses the problems related to data types used for time representation in DEVS, a formalism for the specification and simulation of discrete-event systems. When evaluating a DEVS simulation model into an actual com- puter simulation program, a data type is required to hold the virtual time of the simulation and the time elapsed in the model of the simulated system. We review the commonly data types used, and discuss the problems that each of them induce. In the case of floating point we show how, under cer- tain conditions, the simulation can break causality relations, treat simultaneous events as non simultaneous or treat non simultaneous events as simultaneous. In the case of integers using fixed unit we list a number of problems arising when composing models operating at different timescales. In the case of structures that combine several fields, we show that, at the cost of a lower performance, most of the previous problems can be avoided, although not totally. Finally, we describe an alternative representation data type we devel- oped to cope with the data type problems

Using Finite Forkable DEVS for Decision-Making Based on Time Measured with Uncertainty

International audienceThe time-line in Discrete Event Simulation (DES) is a sequence of events defined in a numerable subset of R +. When it comes from an experimental measurement, the timing of these events has a limited precision. This precision is usually well-known and documented for each instruments and procedures used for collecting experimental datas. Therefore, these instruments and procedures produce measurement results expressed using values each associated with an uncertainty quantification, given by uncertainty intervals. Tools have been developed in Continuous Systems modeling for deriving the uncertainty intervals of the final results corresponding to the propagation of the uncertainty intervals being evaluated. These tools cannot be used in DES as they are defined, and no alternative tools that would apply to DES have been developed yet. In this paper, we propose simulation algorithms, based on the Discrete Event System Specification (DEVS) formalism, that can be used to simulate and obtain every possible output and state trajecto-ries of simulations that receive input values with uncertainty quantification. Then, we present a subclass of DEVS models , called Finite Forkable DEVS (FF-DEVS), that can be simulated by the proposed algorithms. This subclass ensures that the simulation is forking only a finite number of processes for each simulation step. Finally, we discuss the simulation of a traffic light model and show the trajectories obtained when it is subject to input uncertainty

Sequential PDEVS Architecture

International audienceParallel Discrete Event System Specification (PDEVS) is a well-known formalism used to model and simulate Discrete Event Systems. This formalism uses an abstract simulator that defines a set of abstract algorithms that are parallel by nature. To implement simulators using these abstract algorithms , several architectures were proposed. Most of these architectures follow distributed approaches that may not be appropriate for single core processors or microcontrollers. In order to reuse efficiently PDEVS models in this type of systems, we define a new architecture that provides a single threaded execution by passing messages in a call/return fashion to simplify the execution time analysis

An Investigation on Software-Defined Networks’ Reactive Routing against BitTorrent

International audienceTechnologies in Software-Defined Networks (SDNs) introduce program-matic ways to reorganize the network logical topology. A possible practical usage of SDNs is Reactive Routing, where the logical topology is continuously evolving based on traffic statistics and policies. Usually, the SDNs controllers are considered transparent to the higher layers. It is expected that changes in logical topology may not affect applications. Our goal is to study the impact of logical topology changes on BitTorrent, a popular peer-to-peer protocol in practice. In this paper, we focus on BitTorrent and the experimental results show that BitTorrent may produce the opposite effect to the one expected. We have run 32 BitTorrent clients in an emulated SDN ring topology and changed the virtual topology periodically by removing one link at the time from the ring. The experiments produced lower propagation when logical topology changed periodically than when it was static for BitTorrent traffic. For comparison, we recreated the same experiments using HTTP. For HTTP, we obtained slower propagation when logical topology changed than when it was static. We discuss the results and conclude that high layer protocols need to be carefully studied, and in some cases adapted, before being deployed in SDNs

Discrete events cellular models with explicit delays

This work is devoted to introduce several formal descriptions used to model and simúlate cell-shaped spaces. The paradigms are based on the DEVS and Cellular Autómata formalisms, combined with transport delays and inertial delays. The speciñcation formalisms have been deñned for binary or three-states cell spaces, and have been extended to other domains. The delay concepts belong to the digital circuits domain, and have been adapted to the Cellular Autómata paradigm, being one of the main contributions of the present work. The formalims allow the automatic deñnition for the cell spaces, easing the model veriñcation, allowing the cost-effective development of simulators. A tool was built with the goal to implement the formalism, allowing to verify em- pirically the performance of the proposed Solutions

Cell-DEVS Modeling of Environmental Applications

Recently, different research teams used Cellular models for the analysis of environmental systemsusing Cellular models. Some of these techniques are based on Cellular Automata, which have some problemsconstraining its power, usability and feasibility for studying large complex systems. In other cases, the CellularAutomata have been combined with the DEVS (Discrete-Event Systems Specifications) formalism, which requiresexpertise in advanced programming techniques, visualization, distributed computing, etc. Instead, theCell-DEVS formalism and the CD++ toolkit Cell-DEVS simplify the construction of complex cellular modelsby allowing simple and more intuitive model specification. We present the definition of different models, focusingon how to define such applications using Cell-DEVS methodology

Discrete events cellular models with explicit delays

This work is devoted to introduce several formal descriptions used to model and simúlate cell-shaped spaces. The paradigms are based on the DEVS and Cellular Autómata formalisms, combined with transport delays and inertial delays. The speciñcation formalisms have been deñned for binary or three-states cell spaces, and have been extended to other domains. The delay concepts belong to the digital circuits domain, and have been adapted to the Cellular Autómata paradigm, being one of the main contributions of the present work. The formalims allow the automatic deñnition for the cell spaces, easing the model veriñcation, allowing the cost-effective development of simulators. A tool was built with the goal to implement the formalism, allowing to verify em- pirically the performance of the proposed Solutions.Sociedad Argentina de Informática e Investigación Operativ

Modelado e implementación computacional de la propagación de las enfermedades de tranmisión sexual por autómatas celulares (Cell-DEVS)

En este trabajo se realizó un modelo computacional a través de los Autómatas Celulares que puede describir la dinámica de cómo se propagan las enfermedades de transmisión de sexual considerando una subclasificación para la población de infectados (curable y no curable). Así mismo, se ha considerado en este trabajo la perspectiva de la epidemiología matemática del modelo matemático SIS de W.O. Kermack y A.G. McKendrick que representa la dinámica de la epidemia, siendo posible así analizar el comportamiento de la propagación de la epidemia en el tiempo