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SUMMARYDistributed simulation applications often rely on middleware to provide services to support their execution over distributed computing environments. Such middleware spans many levels, ranging from lowlevel support for data transmission through object request brokers to higher level, simulation specific functionality such as time management. We discuss design alternatives for realizing such middleware for hard real-time distributed simulations such as hardware-in-the-loop applications. We present the results from tests of a prototype implementation of real-time Run-Time Infrastructure middleware. Its performance is compared with a non-real-time implementation.

We present a case study in which we apply parallel simulation methods and interoperability techniques to network simulations for simulation-based on-line control of military communication networks.The on-line simulations model actual military networks, including wired shipboard sub-networks connected via satellite links, and wireless mobile devices. The modeled scenario depicts the communication requirements of an amphibious landing where a complex network connects troops ashore and naval vessels. The simulations use a heterogeneous set of tools, including ns2 models for shipboard wired networks, and GloMoSim models for the wireless devices. In this paper, we document the challenges we encountered in applying parallel and interoperable simulation methods, and describe our solutions. We describe our experiences in addressing the interoperability problems that naturally arose due to the heterogeneity of scenario models. We also present a preliminary study on the scalability of real-time performance of parallel network simulations, which is crucial for on-line simulations.Salient system characteristics of the subject military network scenarios are described for the benefit of exposure to the modeling and simulation research community. Our exercise not only highlights the relevance of parallel and distributed simulation techniques to an important real-life problem, but also demonstrates the feasibility of applying those techniques in a practical setting.

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