The NATO STANAG 4603 states that:
Participating nations agree that procurement and new development of simulation systems are compliant with the latest version of IEEE 1516 (HLA).
Participating nations agree to utilize the HLA Compliance Certification Process established by the NATO Modeling and Simulation Group (NMSG).
HLA is an open international standard, developed by the Simulation Interoperability Standards Organization (SISO) and published by IEEE. The standards defines the components of HLA and what interfaces and properties they have.
HLA is a service-oriented architecture with a distributed enterprise service bus (HLA Runtime Infrastructure - RTI) that provides M&S services to participating systems (federates). Separate agreements (Federation Agreements) define how to use the more general HLA services and a detailed model (Federation Object Model - FOM) describe what type of information is exchanged in the distributed simulation (Federation).
STANREC 4800 AMSP-04 NATO Education and Training Network Federation Architecture and FOM Design (NETN FAFD) is a NATO recommended reference Federation Agreement.