Hierarchical optimistic distributed simulation: Combining DEVS and Time Warp.

Abstract

Conventional simulation environments and languages do not provide a unified approach to system decomposition and modelling. Also noticeably lacking is the support for model reuse. In this time of constrained resources--people, time, money--it is imperative that the new methodologies present in parallel computing, software engineering, and artificial intelligence be applied to the modelling and simulation domain. Additionally modelling and simulation must move from one time modelling efforts in isolation to an integrated multifaceted system modelling approach maximizing model reuse and optimizing the constrained resources. This dissertation reviews the concepts of Discrete Event System Specification (DEVS) formalism and its associated abstract simulator concepts, the Ada programming language, and the conservative and optimistic distributed simulation paradigms. Then requirements for a distributed modelling and simulation environment which incorporate the new methodologies present in parallel computing, software engineering and artificial intelligence are proposed. A hierarchical optimistic distributed modelling and simulation environment is implemented in Ada. The environment combines the DEVS formalism and its associated abstract simulators with the Time Warp optimistic distributed simulation paradigm. The implemented modelling and simulation environment (DEVS-Ada) is then examined with respect to how it meets the requirements for a distributed modelling and simulation environment. A simulation study is conducted measuring the performance of the nondistributed versus distributed implementations of DEVS-Ada using the replicative validation of a Single Server Without Queue model. Additional studies are conducted examining the effect of model to processor mappings, and the use of flat versus hierarchical models.