DIS - Distributed Interactive Simulation
DIS, or Distributed Interactive Simulation, is a standard networking protocol for exchanging information among various simulation applications. It defines a set of Protocol Data Units, or PDUs, for publishing Entity State information, Fire and Detonate events, Logistics information, Emissions and Communications data, and more. The DIS protocol was defined through an open standards development process, with participation by government, industry, and academia.
HLA - High Level Architecture
The HLA (High Level Architecture) is a more recent standard for interoperability among simulations. Rather than a networking protocol (wire standard) like DIS, HLA defines an architecture with a set of API (Application Programmer's Interface) Standards. Simulation applications (known as federates in HLA) communicate by making calls to the HLA APIs. A piece of software known as the RTI (Run-time Infrastructure) implements the HLA API, and is responsible for transporting data from one federate to another. Like DIS, the HLA Standards are owned by IEEE. There are three documents that comprise the HLA Standard, all available from IEEE.
RPR FOM – Real-time Platform-level Reference Federation Object Model
While the HLA Standards dictate how federates exchange data, it is a FOM (Federation Object Model) that dictates what data is being exchanged in a particular federation. HLA does not mandate the use of any particular FOM, however, several "reference FOMs" have been developed to promote a-priori interoperability. That is, in order to communicate, a set of federates must agree on a common FOM (among other things), and reference FOMs provide ready-made FOMs that are supported by a wide variety of tools and federates. Reference FOMs can be used as-is, or can be extended to add new simulation concepts that are specific to a particular federation or simulation domain.
DLC API – Dynamic Link Compatible (DLC) HLA API
The version of the C++ API for HLA that was defined by IEEE 1516.1-2000 does not support Dynamic-Link Compatibility among RTI implementations. That is, it is not possible for a federation to switch from one RTI implementation to another without recompiling federates. This limitation is more serious than it sounds, because it takes the choice of which RTI to support out of the hands of the end-user. The program manager for a federation must convince federate providers and tool vendors to build specifically for the RTI he chooses.