Alessandra Pieroni

Simulation model building of traffic intersections

Designers of traffic systems might take advantage of the simulation-before-construction approach that allows them to study the behavior of a new or existing system by use of simulation models. Nevertheless, the use of simulation models is often hindered by the fact that the model building activity is a critical, time consuming and error prone activity if performed by use of experience and intuition only. Moreover, traffic designers do not usually have the necessary skills to effectively carry out system simulation. This paper overcomes such problems by introducing a model building method, thus enabling traffic designers to seamlessly introduce simulation-before-construction into their best practices. The method is applied to the building of simulation models of traffic intersections, with an example application to a real-world intersection.

A model-driven method for building distributed simulation systems from business process models

The analysis of modern business processes implemented as orchestration of software services demands for new approaches that explicitly take into account the inherent complexity and distribution characteristics of such processes. In this respect, Distributed Simulation (DS) offers a viable tool to cope with such a demand, due to the aggregation, scalability, representativeness and load balancing properties that it allows to achieve. However, the use of DS is mostly limited by the specialized technical know-how and the extra-development that DS requires with respect to approaches based on conventional local simulation. This paper proposes a model-driven method that enables the DS-based analysis of business processes by introducing the automated transformation of business process models into analysis models that are specified as Extended Queueing Network (EQN) models and executed as distributed simulations. The paper also presents an example application to a business process for an e-commerce scenario.

A MDA-based approach for the development of DEVS/SOA simulations

The intrinsic complexity of the DEVS formalism and the manual production of DEVS-based simulations might constitute obstacles to the adoption of DEVS for both system modelers and simulation users. To overcome these obstacles, this paper introduces a model-driven approach for the development of DEVS simulations. The approach provides modelers and users with standard graphical modeling languages and with model transformation specifications for automated code production. Specifically, the approach enables the UML specification of DEVS models and automates the generation of DEVS simulations that make use of the DEVS/SOA implementation. An example application to the production of a DEVS/SOA simulation for a basic queuing system is also presented, to show the details of the proposed approach.

Producing Simulation Sequences by Use of a Java-Based Generalized Framework

The quality and representativeness of simulation results heavily depend on the sequence of numbers used in the experiments. When dealing with simulations of critical systems, it might be necessary to increase the representativeness of such results by running experiments with different sequences and to investigate the system behaviour in specific situations. In large models, however, managing sequence of numbers could become cumbersome and could attract the attention of simulation system developers on the input settings instead of model logic. In this paper, we present a component-based framework for sequence of numbers that offers a high degree of flexibility and raises the simulation system developers from the details of the input sequences while implementing the model logic. The sequences can be thus configured in a following phase and deployed in the simulation systems with almost no effort.

Distributed simulation of complex systems by use of an HLA-transparent simulation language

The continuously decreasing cost of distributed systems gives academics and industry the advantage of using larger execution platforms and of reusing locally implemented software components. This is particularly true for the simulation of complex systems where the computational resources needed considerably increase with the model resolution and with the number of simulated entities. The development of such simulation systems, however, requires extra efforts compared to the conventional local ones. Example extra efforts are learning how to use the Distributed Simulation (DS) Standard (such as HLA) and the development of extra software for the synchronization and communication between the local and distributed environment. In this paper, we address the problem of defining a simulation language that can transparently support the development distributed simulation systems, by making the use of the DS standard transparent and also reducing the amount of extra software. The HLA transparent language we introduce is named jEQN, being Java-based and dealing with Extended Queueing Networks domains. The language approach, however, can be easily extended to any other DS Standard and modelling domain.

Energy saving in data processing and communication systems.

The power management of ICT systems, that is, data processing (Dp) and telecommunication (Tlc) systems, is becoming a relevant problem in economical terms. Dp systems totalize millions of servers and associated subsystems (processors, monitors, storage devices, etc.) all over the world that need to be electrically powered. Dp systems are also used in the government of Tlc systems, which, besides requiring Dp electrical power, also require Tlc-specific power, both for mobile networks (with their cell-phone towers and associated subsystems: base stations, subscriber stations, switching nodes, etc.) and for wired networks (with their routers, gateways, switches, etc.). ICT research is thus expected to investigate into methods to reduce Dp- and Tlc-specific power consumption. However, saving power may turn into waste of performance, in other words, into waste of ICT quality of service (QoS). This paper investigates the Dp and Tlc power management policies that look at compromises between power saving and QoS.

Power Management of Server Farms

The power management of server farms (Sf) is becoming a relevant problem in economical terms. Server farms totalize millions of servers all over the world that need to be electrically powered. Research is thus expected to investigate into methods to reduce Sf power consumption. However, saving power may turn into waste of performance (high response_times), in other words, into waste of Sf Quality of Service (QoS). By use of a Sfmodel, this paper investigates Sf power management strategies that look at compromises between power-saving and QoS. Various optimizing Sf power management policies are studied combined with the effects of job queueing disciplines. The (policy, discipline) pairs, or strategies, that optimize the Sf power consumption (minimum absorbed Watts), the Sf performance (minimum response_time), and the Sf performance-per-Watt (minimum response_time-per-Watt) are identified.By use of the model, the work the server-manager has to do to direct hisSf is greatly simplified, since the universe of all possible (strategies he needs to choose from is drastically reduced to a very small set of most significant strategies.

A Distributed Approach to Wireless System Simulation

Many papers have been published that present simulation results for wireless systems, including WiMAX. All such papers do not deal with wireless simulation approaches, and simulation is only seen as a side-means to produce numerical results. This paper does not present simulation numerical predictions. It instead deals with new simulation approaches for wireless systems and presents simulation software technologies. From the approach point of view, the “local” versus the “ distributed” simulation approach is investigated to wireless systems. From the technology point of view, two new software tools are presented, for a step forward with respect to existing tools to ease the development of distributed simulation systems. The tools consist of a new distributed simulation environment (wDSEnv) and a new distributed simulation language (wDSLang). Such tools are described and a detailed WiMAX local and distributed simulation example is developed.

A distributed approach to the simulation of inherently distributed systems

Inherently distributed systems are systems that are distributed by their own nature; in other words, they are composed of subsystems, which are physically and geographically separated. Examples of such systems are the distributed computer systems with various hosts geographically located; the wireless systems with a number of base and subscriber stations geographically separated; the satellite constellations, the military battlefields and so on. Such systems have, in many cases, been studied by use of Local Simulation (LS), in other words, a simulation run by a single host, or by use of Distributed Simulation (DS) in which the simulation system is divided into a number of federates, run by separate hosts for the scope of obtaining resource scalability and simulator reusability. In this paper, the DS approach is seen from a different point of view: a way to give higher representativeness to the simulation of inherently distributed systems. The approach consists of locating the federates in the same geographic positions of the subsystems that are designed to become part of the inherently distributed system. In this way, the distributed system can be studied in a very realistic way before being implemented. In this paper the problems and the advantages of this new DS approach are discussed and the technology is presented that supports and facilitates its introduction.

HLA-Transparent Distributed Simulation of Agent-based Systems

The adoption of the agent-based approach to the modelling and simulation of physical systems has proved to considerably increase the simulation realism and accuracy. Simulation systems of such a kind, however, require computational resources that might become unfeasible when the number of simulated agents scales up. A Distributed Simulation (DS) approach might improve the execution of such systems, particularly in the case of scenarios populated by a large number of agents. Building an agent-based DS system, however, requires both specific expertise and knowledge of distributed simulation standards and a non-negligible amount of effort with respect to conventional local simulation systems. In this book chapter, we introduce a simulation framework named Transparent_DS (TDS), which enables the use of distributed environments while making affordable the development of agent-based simulators. TDS raises developers from the specific issues of the distributed environment. By use of TDS, the simulation agents can be locally developed and tested, and then transparently deployed in a DS environment, bringing significant savings in terms of effort and development time. In addition, TDS provides a uniform interface to the JADE framework, which further facilitates the work of developers of JADE-based Multi-Agent Systems (MAS) in the production of agent-based DS systems. By the TDS approach, any HLAand agent-based distributed simulation system can practically be developed as conventional local MAS, with no extra effort and no extra knowledge. An example development of a simulation system is presented which is a common abstraction in several domains that involve the motion of individuals in a multistorey building to simulate operations in normal or emergency situations.