Development and Evaluation of Parallel and Distributed Simulation with Web services

TAEJONG YOOa,*, HYUNBO CHOa, ENVER YÜCESANb

aDepartment of Industrial Engineering

Pohang University of Science and Technology San 31 Hyoja, Pohang 790-784

SOUTH KOREA bTechnology and Operations Management Area

INSEAD Boulevard de Constance 77305, Fontainebleau Cedex

FRANCE

Abstract: Parallel and distributed simulation is concerned with the efficient execution of large-scale discrete event simulation models on multiprocessors and distributed platforms. After the development of World Wide Web (WWW), many efforts in parallel and distributed simulation have been made for modeling, particularly building simulation languages and creating model libraries that can be assembled and executed over WWW, and for analysis, particularly developing simulation optimization algorithms for parallel and distributed experimentation. These efforts have thus far produced mixed results. However, the recent advent of XML and web services technology provides enhanced opportunities for web-based distributed simulation. Especially, web services as a distributed information technology possess powerful capabilities for scalable interoperation of heterogeneous systems. This paper aims to develop and evaluate parallel and distributed simulation using the web services technology for efficient simulation execution. In particular, a prototype framework is implemented using web services for a simple shop floor simulation, where we focus on web-based simulation optimization through the distribution of simulation replications across different servers. The development of parallel and distributed simulation using web services will help to solve large-scale problems efficiently and guarantee interoperability among heterogeneous networked systems. Key-Words: Web services, Parallel and distributed simulation, OCBA, Simulation optimization. 1 Introduction Discrete Event Simulation (DES) is arguably the most popular approach for modeling and analysis of man-made systems such as communication networks, traffic systems, and manufacturing facilities. In addition to its ability to incorporate arbitrary levels of system complexity, which is typically outside the scope of analytical models, DES is concerned with the modeling of a system as it evolves over time. A common goal of DES is to choose the best among a set of competing alternatives. To obtain good statistical estimates for each alternative, a large number of replications must be conducted. In fact, high accuracy requirements together with a large number of competing alternatives would typically lead into significant computational load. Consequently, to reduce the computational load can be a worthwhile subject to investigate [5].

One way to speed up the execution of large-scale simulations is to distribute the simulation runs to several different processors and conduct the simulation experiments in a parallel fashion. The focus of parallel and distributed simulation research has historically been centered on parallel and distributed implementations of sequential simulation models that result in speed up of model execution at runtime. Parallel DES programs are executed on multi-processor computing platforms with multiple central processing units that interact frequently. Distributed DES programs, on the other hand, are executed on loosely coupled systems that may be geographically distributed and require longer interaction times. In particular, with the development of WWW, many efforts in parallel and distributed simulation have been made for modeling, building simulation languages and

Proceedings of the 8th WSEAS Int. Conference on Automatic Control, Modeling and Simulation, Prague, Czech Republic, March 12-14, 2006 (pp152-157)

creating model libraries that can be assembled and executed over the web, and for analysis, particularly developing simulation optimization algorithms for parallel and distributed experimentation. However, because simulation languages or model libraries for the parallel and distributed simulation are restricted by the specific characteristics of the language or the platform, the applicability of web-based simulation has traditionally been limited. The recent advent of XML and web services technology provides an immense potential for providing interoperability among heterogeneous information systems. The objective of the paper is to develop and evaluate an efficient distributed simulation platform using the web services technology: (1) to implement a prototype of the interoperable distributed simulation platform via web services, and (2) to improve the statistical efficiency of simulation optimization via distributed simulation. The remainder of the paper is organized as follows. Section 2 presents a survey of the relevant literature. Section 3 proposes the framework of web services-based parallel and distributed simulation. The algorithm for simulation execution is discussed in Section 4. The prototype implementation is described in Section 5. Preliminary experimental results are presented in Section 6. Finally, Section 7 provides the current research efforts and future work. 2 Related Work 2.1 Web-based Parallel and Distributed

Simulation The topic of web-based simulation spans a variety of areas. In particular, web-based simulation requires the convergence of parallel and distributed simulation methodology and WWW technology. Web-based parallel and distributed simulation can have the added feature of code mobility afforded by such network programming languages as Java or network package as Parallel Virtual Machine (PVM). Especially, Java-based simulation libraries are emerging that permit the creation of simulation programs as Java applications and applets. Among these are Simkit, JavaSim, JSIM and Simjava. One of the primary advantages of these packages is that they permit network-based simulation models to be developed [7]. 2.2 Web Services

The fundamental idea of web services is to integrate software applications as services. A web service is a universally accessible software component deployed on WWW. Such a software component is described by an interface listing the collection of operations that can be performed on it [1]. Web services allow the applications to communicate with other applications using open standards. Web services are based on standard technologies: communication protocol (Simple Object Access Protocol, SOAP), service description (Web Services Description Language, WSDL), and service discovery (Universal Description, Discovery and Integration, UDDI). This way web services can communicate with each other even if they are running on different operating systems or written in different languages. With these characteristics, Web services provide a natural infrastructure for distributed web-based simulation reducing the distinction between PADS and DIS. The synergies between web service and distributed simulation are detailed in. 2.3 Simulation Optimization In discrete event simulation optimization, ranking and selection procedures are commonly applied for selecting the best alternative from among a finite set of competing alternatives [5]. In ranking and selection, the probability of correct selection, where ‘correct selection’ is defined as the event that the selected best alternative is the true best alternative, is used to determine the additional number of replications. Due to the stochastic nature of discrete event simulation, the total number of replications required for each alternative to achieve the desired probability of correct selection may be significant. Optimal Computing Budget Allocation (OCBA) is one of the new approaches aimed at improving the efficiency of ranking and selection [2]. Instead of allocating an equal number of simulation replications to each alternative, the OCBA employs a sequential approach to attain the desired correct selection probability. At the initialization stage, a small number of replications are performed for each alternative to estimate the mean and the variance of the performance measures. 3 Framework of Proposed PADS In the present work, parallel and distributed simulation based on web services is proposed to improve the efficiency of ranking and selection procedures. In

Proceedings of the 8th WSEAS Int. Conference on Automatic Control, Modeling and Simulation, Prague, Czech Republic, March 12-14, 2006 (pp152-157)