Time Management

Professor Fujimoto has been working with the Defense Modeling and Simulation Office (DMSO) on the specification of the time management services of the HLA. Time management is concerned with the mechanisms used by simulations to advance through simulation time. It is concerned with issues such as synchronization (concurrency control) and message ordering to ensure that the simulation preserves before-and-after relationships in the system to an acceptable level consistent with the goals of the federation execution. The strategy that has been developed provides a variety of message delivery services that trade off latency and preservation of before-and-after relationships. For example, training simulations and test and evaluation simulations with hard real-time constraints will generally utilize the receive order service that provides minimal latency, but virtually no guarantees with respect to order preservation. On the other hand, classical discrete event simulations (e.g., war gaming simulations) will typically use the time stamp delivery order that preserves ordering relationships, but at the cost of higher message latency. The time management structure supports both conservative (blocking based) and optimistic (rollback based) synchronization among the simulations.