Approximate Distributed Discrete Event Simulation using SemiConservative LookAhead Estimation A novel way of distributed discrete event simulation, called approximate distributed discrete event simulation, is presented in this paper. Compared with the classic simulation, the models for approximate simulation give some kind of free margin to the simulator during the execution. This can be used in some cases to reduce the overhead of the simulation, especially the execution time. Since the margin can be adjusted arbitrarily in the range, a tradeoff between the simulation precision and the execution time can be achieved this way. Itxe2x80x99s well known that the execution time of distributed discrete event simulation canxe2x80x99t be reduced significantly compared with a sequential simulation when the logical processes are tightly coupled and the lookahead is very short. In this study, a framework of approximate distributed discrete event simulation with some novel algorithms is developed, which is aimed to provide a longer lookahead and further the tradeoff between the simulation precision and the execution time using the free margin provided by the model.

StateEstimation for DelayManagement in Distributed RealTime CoSimulation via the Internet Typical distributed embedded realtime systems are composed of several subsystems developed by different, geographically distributed manufacturers. During the development process, these subsystems have to be integrated via realtime communication networks and tested. The verification can be simplified combining cosimulation and Software and HardwareInTheLoop (SILHIL) testing in a distributed cosimulation framework. In such a framework, software (SIL) and hardware (HIL) components can be tested against the model of a simulated plant. This way it is possible to detect design faults and integration problems while the subsystems are still located at their manufacturersxe2x80x99 sites.Realtime systems impose strict temporal and reliability requirements on the communication network connecting the subsystems. However, these requirements cannot be achieved using the Internet for communication in the distributed cosimulation framework. In this paper we introduce stateestimation as a delaymanagement technique to provide required subsystem inputs in time. Based on previous outputs and a simulation model of the remaining system, the mechanism estimates a subsystemxe2x80x99s future inputs. Using scheduling information about the realtime communication in the system, the framework can determine if an input packet is received in time. If not, the estimated packet is forwarded. As soon as the real input packet is received later, its content is compared with the estimated input and the operator is notified if the error between estimated and real input exceeds a configurable threshold.