Research On Time Management Services In Runtime Infrastructure For Distributed Simulations

High Level Architecture (HLA) is a distributed modeling and simulation standard put forward by American Department of Defense, which is used to facilitate interoperability and reuse of various models and simulations among themselves and with C4I-systems. HLA was adopted as the IEEE 1516 standard in September 2000. Time Management services in HLA is brought forward on the basis of all kinds of former time management technologies. The main goal of time management services is used to resolve time stamp order of messages in a distributed simulation, and ensures that the simulation can be executed correctly.Time management services is the critical technology in HLA/RTI, while the research on the principles and key algorithms in time management services is a well-known important and intractable problem in present modeling and simulation area. Especially with the frequent rise of simulation scales, the actual application of time management services is also meeting an unprecedented challenge.The objective of the dissertation is to study the efficient time management services for large-scale distributed simulations. The major contributions of this thesis focuses on the principles and key algorithms in time management services according to the IEEE 1516 standard, and the implementation mechanisms in a hierarchical RTI (Runtime Infrastructure) software named StarLink+ based on CORBA (Common Object Request Broker Architecture).It is most important for GALT (Greatest Available Logical Time) algorithm to implement time management services which is also called LBTS (Lower Bound Time Stamp) in HLA 1.3. In order to resolve the deadlock which may exist in a GALT algorithm, this thesis systematically analyzes the factors of GALT computation, anatomizes a few of algorithms' shortages, reveals some important conclusions about the deadlock, and Two GALT algorithms without deadlock are put forward, which are called stature-measuring I and stature-measuring II. The correctness of the two algorithms are also proved, and they can exactly provide reliable technology support to develop time management services according to IEEE 1516.The optimistic advancing mechanism in HLA originally comes from PDES (Parallel Discrete Event Simulation), but they are not always the same. In order to resolve the complicated implementation of rollback mechanism with low efficiency, this thesis analyzes and compares the two different optimistic advancing mechanisms in PDES and HLA, reveals some important differences between them, explains the programming method for a simulation application and the Zero-Saving mechanism without saving any operations in a RTI is proposed. The Zero-Saving mechanism can simplify the development of time management services in a RTI greatly.A hierarchical RTI can effectively decrease the computation expenditure in timemanagement services, and support the large-scale simulations. The hierarchical architecture in StarLink+ is composed of three levels that are the central RTI server (CRTI), the local RTI servers (LRTI), and the joined federates. In order to resolve the great expenditure in time management services for large-scale simulations, this thesis proposes and implements two schemes in time management services according to IEEE 1516 standard based on the hierarchical RTI architecture. One is the central scheme and the other is the distributed scheme. The dissertation also describes the algorithms of all important time management services in the two schemes in details.The double-level parallel advancing technology based on the two least elements is put forward in the central scheme. Time advancement is controlled by the central RTI server and all local RTI servers, and the technology can greatly enhance the decision-making efficiency. When a joined federate requests to advance time, its local RTI server firstly makes rapid decision and decides whether the joined federate can be granted to advance logical time. If the local RTI server suspends the request, the central RTI server must dispose the request globally. As it has all informa...