Richard M. Weatherly

The Department of Defense High Level Architecture

The High Level Architecture (HLA) provides the specification of a common technical architecture for use across all classes of simulations in the US Department of Defense. It provides the structural basis for simulation interoperability. The baseline definition of the HLA includes (1) the HLA Rules, (2) the HLA Interface Specification, and (3) the HLA Object Model Template. This paper describes the motivations and processes used to develop the High Level Architecture and provides a technical description of key elements of the architecture and supporting software. Services defined in the interface specification for providing time management (TM) and data distribution management (DDM) for distributed simulations are described.

Time management in the DoD high level architecture

Recently, a considerable amount of effort in the U.S. Department of Defense has been devoted to defining the High Level Architecture (HLA) for distributed simulations. This paper describes the time management component of the HLA that defines the means by which individual simulations (called federates) advance through time. Time management includes synchronization mechanisms to ensure event ordering when this is needed. The principal challenge of the time management structure is to support interoperability among federates using different local time management mechanisms such as that used in DIS, conservative and optimistic mechanisms developed in the parallel simulation community, and real-time hardware-in-the-loop simulations.

Standards for simulation : As simple as possible but not simpler the high level architecture for simulation

The High Level Architecture (HLA) is an architec ture for reuse and interoperation of simulations. It is based on the premise that no simulation can satisfy all uses and users. An individual simulation or set of simulations developed for one purpose can be applied to another application under the HLA concept of the federation: a composable set of interacting simula tions. The intent of the HLA is a structure which will support reuse of capabilities available in differ ent simulations, ultimately reducing the cost and time required to create a synthetic environment for a new purpose, and the possibility of distributed col laborative development of complex simulation appli cations. The HLA is widely applicable across a full range of simulation application areas. The widely differing application areas indicate the variety of re quirements that have been considered in develop ment and evolution of the HLA. The HLA does not prescribe a specific implementation, nor does it man date the use of any particular software or program ming language. Over time, as technology advances, new and different implementations will be possible within the HLA framework. This paper describes the technical motivations for the HLA, the key elements of the architecture and how they are minimum and essential to the goal of reuse and interoperability.

The DoD high level architecture: an update

The DoD High Level Architecture (HLA) provides the specification of a common technical architecture for use across all classes of simulations in the US Department of Defense. It provides the structural basis for simulation interoperability. The baseline definition of the HLA includes the HLA rules, the HLA interface specification (IFSpec), and the HLA object model template (OMT). The HLA rules are a set of 10 basic rules that define key principles used in the HLA as well as the responsibilities and relationships among the components of an HLA federation. The HLA IFSpec provides a specification of the functional interfaces between HLA federates and the HLA runtime infrastructure. The HLA OMT provides a common presentation format for HLA simulation and federation object models. The paper provides a description of the development of the HLA, a technical description of the key elements of the architecture, and a discussion of HLA implementation, including HLA support processes and software.

The aggregate level simulation protocol: an evolving system

The aggregate level simulation protocol (ALSP) concept was initiated by ARPA in January 1990, the first laboratory demonstration took place in January 1991, and the first fielding in support of a major military exercise took place in July 1992. Since then, the ALSP confederation of models has grown from the original two members to six. In support of this growing confederation, the ALSP Infrastructure Software (AIS) has evolved from its fundamental functionality to the current focus on improved confederation management and performance. This paper describes the evolution of the AIS from the initial prototype to the present, emphasizing the discovery of new requirements and how they were accommodated.

Design and implementation of HLA time management in the RTI version F.0

The DoD High Level architecture (HLA) has recently become the required method for the interconnection of all DoD computer simulations. The HLA addresses the rules by which simulations are designed to facilitate interoperability, the method by which information exchanged between simulations is described, and a standard set of software services provided 5y a common Runtime Infrastructure (RTI). The RTI is responsible for the coordination of collections of cooperating simulations. The familiarization version of the RTI, dubbed F.0, was developed at the MITRE Corporation. One of the core components of the RTI is Time Management and is the focus of this paper. In particular, we present the design and algorithms used to implement the HLA Time Management Services in F.O.

ALSP—theory, experience, and future directions

The Aggregate Level Simulation Protocol (ALSP) interface technique is now entering its second year of practical application. ALSP is designed to permit multiple, pre-existing combat simulations to interact with each other over local and wide area networks. Army, Navy, and Air Force, simulations have been linked, using ALSP, to form a confederation of models capable of supporting major military exercises. This exercise experience has reinforced many of the initial ALSP design decisions, called others into question, and revealed some new requirements. The basic ALSP system software services, practical features derived of operational experience, and the current research efforts are described.

A reusable architecture for simulations

HLA has wide applicability across a full range of simulation areas, including education, training, analysis, engineering, and even entertainment. These widely differing applications indicate the variety of requirements considered in the development and evolution of HLA. DMT is one among the many applications that are based on HLA. HLA does not prescribe a specific implementation, nor does it mandate the use of any particular software or programming language. Over time, as technology advances, new and different implementations will be possible within the framework of HLA. The motivation behind HLA is a common architecture will allow leveraging investments in simulation capabilities to meet new and changing user needs. Further, by standardizing only key elements of the architecture and not implementation, supporting software developments can be tailored to the performance needs of applications. These can also capitalize on the emerging improvements in processor and network technologies. This article outlines the key features of HLA, the rationale for its design and development, and its application to DMT. In particular, the discussion focuses on issues facing the DMT community and the ways that HLA supports the development of approaches to them. The HLA development process involved govJudith S. Dahmann, James O. Calvin, and Richard M. Weatherly

Automated distributed system testing: designing an RTI verification system

A project is currently underway which involves testing a distributed system-the Run Time Infrastructure (RTI) component of the High Level Architecture (HLA). As part of this effort, a test suite has been designed and implemented to provide a coordinated and automated approach to testing this distributed system. This suite includes the creation and application of a Script Definition Language (SDL) to specify test sequences, and a test executive to control execution of the tests, coordinate the test environment, and record test results. This paper describes the design and implementation of this test environment.

Efficient process interaction simulation in Java: implementing co-routines within a single Java thread

The genesis of a research effort to develop a Java-based process-oriented simulation framework is described. A key enabler to the framework is an efficient co-routine mechanism implemented within the context of a single Java thread. A design for such a co-routine mechanism is described and some initial results of an implementation within the IBM Jikes reference virtual machine are given.