The chapter provides an overview of parallel and distributed simulation systems, which have evolved significantly since the 1970s and 1980s. These systems are used in various applications, including military training, communication network analysis, and air traffic control. The focus is on technologies that distribute the execution of simulation programs across multiple computer systems, with a particular emphasis on synchronization algorithms and data distribution techniques. **Parallel and Distributed Simulation:** - **Parallel Simulation:** Involves execution on multiprocessor platforms with frequent interactions. - **Distributed Simulation:** Involves execution on loosely coupled systems with less frequent interactions, often over wide area networks. **Applications:** - **Analytical Simulations:** Used for evaluation and analysis, aiming to reduce execution time. - **Online Simulations:** Used for real-time decision-making, requiring very fast execution. - **Virtual Environments:** Used for training, entertainment, and device testing, emphasizing real-time execution and scalability. **Benefits:** - Reduced execution times through parallel processing. - Real-time execution for online simulations. - Scalability and fault tolerance in virtual environments. - Interoperability and integration of diverse simulators. **Synchronization:** - **Conservative Synchronization:** Ensures events are processed in timestamp order, avoiding violations of local causality. - **Optimistic Synchronization:** Allows violations but can detect and recover from them, offering greater parallelism but requiring more memory and complexity. **Time Parallel Simulation:** - Divides the simulated time axis into intervals, assigning each to a different processor. - Challenges include ensuring state matching at interval boundaries. **Distributed Virtual Environments (DVEs):** - Based on the SIMNET project, which demonstrated the viability of distributed simulations for military training. - Standards like DIS and HLA enable interoperability among independently developed simulators. - Key concepts include dead reckoning for position estimation and data distribution for efficient communication. **Data Distribution:** - Essential for scaling DVEs to include more entities and sites. - Challenges include efficient message routing and minimizing communication overhead. - The High Level Architecture (HLA) provides mechanisms for data distribution, including declaration management and data distribution management. **Conclusion:** Parallel and distributed simulation technologies are crucial for high-performance computing and the creation of geographically distributed virtual environments. Synchronization and data distribution are fundamental issues in these systems, with ongoing research aimed at improving efficiency and scalability.The chapter provides an overview of parallel and distributed simulation systems, which have evolved significantly since the 1970s and 1980s. These systems are used in various applications, including military training, communication network analysis, and air traffic control. The focus is on technologies that distribute the execution of simulation programs across multiple computer systems, with a particular emphasis on synchronization algorithms and data distribution techniques. **Parallel and Distributed Simulation:** - **Parallel Simulation:** Involves execution on multiprocessor platforms with frequent interactions. - **Distributed Simulation:** Involves execution on loosely coupled systems with less frequent interactions, often over wide area networks. **Applications:** - **Analytical Simulations:** Used for evaluation and analysis, aiming to reduce execution time. - **Online Simulations:** Used for real-time decision-making, requiring very fast execution. - **Virtual Environments:** Used for training, entertainment, and device testing, emphasizing real-time execution and scalability. **Benefits:** - Reduced execution times through parallel processing. - Real-time execution for online simulations. - Scalability and fault tolerance in virtual environments. - Interoperability and integration of diverse simulators. **Synchronization:** - **Conservative Synchronization:** Ensures events are processed in timestamp order, avoiding violations of local causality. - **Optimistic Synchronization:** Allows violations but can detect and recover from them, offering greater parallelism but requiring more memory and complexity. **Time Parallel Simulation:** - Divides the simulated time axis into intervals, assigning each to a different processor. - Challenges include ensuring state matching at interval boundaries. **Distributed Virtual Environments (DVEs):** - Based on the SIMNET project, which demonstrated the viability of distributed simulations for military training. - Standards like DIS and HLA enable interoperability among independently developed simulators. - Key concepts include dead reckoning for position estimation and data distribution for efficient communication. **Data Distribution:** - Essential for scaling DVEs to include more entities and sites. - Challenges include efficient message routing and minimizing communication overhead. - The High Level Architecture (HLA) provides mechanisms for data distribution, including declaration management and data distribution management. **Conclusion:** Parallel and distributed simulation technologies are crucial for high-performance computing and the creation of geographically distributed virtual environments. Synchronization and data distribution are fundamental issues in these systems, with ongoing research aimed at improving efficiency and scalability.