Optimistic synchronization in the HLA 1516.1-2010 : interoperably challenged
Time Management can be considered as one of the key achievements of the High Level Architecture for Modeling and Simulation (HLA). While HLA’s time management is supposed to offer a unique support for heterogeneous time advancement schemes, its practical use is often limited to conservative time advancement (e.g. using services such as nextMessageRequest/nextMessageRequestAvailable) or time stepped time advancement (e.g. using services such as timeAdvanceRequest/timeAdvanceRequestAvailable). In this paper, we investigate HLA’s capabilities for supporting optimistic time advancement and the interoperability between optimistic and conservative federates. The results are strikingly disappointing. While HLA had initially taken off with the noble vision of federations including both optimistic and conservative federates within a single federation execution, the current implementations of two leading RTI vendors fall short of achieving this objective. Neither do they enable the efficient execution of federations consisting of purely optimistically synchronized federates nor do they facilitate interoperability between optimistic and conservative federates. This paper documents the observed problems and discusses potential limitations in the IEEE HLA 1516.1-2010 specification and its interpretation by RTI vendors.