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MSG-052 Knowledge Network for Federation Architecture and Design

ABSTRACT: Development of distributed simulations is a complex process requiring extensive experience, in-depth knowledge and a certain skills set for the Architecture, Design, development and systems integration required for a federation to meet its operational, functional and technical requirements. Federation architecture and design is the blueprint that forms the basis for federation-wide agreements on how to conceive and build a federation. Architecture and design issues are continuously being addressed during federation development. Knowledge of “good design” is gained through hands-on experience, trial-and-error and experimentation. This kind of knowledge however, is seldom reused and rarely shared in an effective way. This paper presents an ongoing effort conducted by MSG-052 “Knowledge Network for Federation Architecture and Design” within the NATO Research and Technology Organisation (NATO/RTO) Modelling and Simulation group (NMSG).

The main objective of MSG-052 is to initiate a “Knowledge Network” to promote development and sharing of information and knowledge about common federation architecture and design issues among NATO/PfP (Partnership for Peace) countries. By Knowledge Network, we envision a combination of a Community of Practice (CoP), various organisations and Knowledge Bases.

A CoP, consisting of federation development experts from the NATO/PfP nations, will foster the development of stateof- the-art federation architecture and design solutions, and provide a Knowledge Base for the Modelling and Simulation (M&S) community as a whole. As part of the work, existing structures and tools for knowledge capture,
management and utilization will be explored, refined and used when appropriate; for instance the work previously done under MSG-027 PATHFINDER Integration Environment provides lessons learned that could benefit this group.

The paper will explore the concept of a Community of Practice and reveal the ideas and findings within the MSG-052 Management Group concerning ways of establishing and managing a Federation Architecture and Design CoP. It will also offer several views on the concept of operations for a collaborative effort, combining voluntary contributions
as well as assigned tasks. Amongst the preliminary findings was the notion of a Wiki-based Collaborative Environment in which a large portion of our work is conducted and which also represents our current Knowledge Base. Finally, we present some of our main challenges and vision for future work.

Authors: Gunnar Öhlund, Björn Löfstrand, Fawzi Hassaine
Publication: Proceedings of 2007 Fall Simulation Interoperability Workshop, 07F-SIW-024, Simulation Interoperability Standards Organization, September 2007.

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Making Your BOMs and FOM Modules Play Together

ABSTRACT: Proper modeling is key in order to achieve effective interoperability between simulation systems. Base Object Models (BOMs) is a SISO standard that allows simulation developers to create object models that form a base or interoperability, even though the participating systems to be used have not yet been selected. The BOM concept is based on the assumption that piece-parts of models, simulations, and federations can be extracted and reused as modeling building-blocks or components. Special attention is paid to sequences of events that take place between simulation elements.

An important part of the High Level Architecture standard is the Federation Object Model (FOM) that describes the data to be exchanged at runtime. The upcoming version of HLA, named “HLA Evolved”, allows FOMs to be divided into smaller, reusable components called FOM modules.

BOMs have unique capabilities in the earlier phases of FEDEP since they enable reuse across federations and have little dependency on the exact systems that are used in any particular federation. FOM Modules on the other hand have unique capabilities during the later phases since they can provide plug-and-play reuse. The greatest benefit is achieved if they are used together. BOMs and Modular FOMs also share a number of description formats that enables a smooth transition from BOMs to FOM Modules.

This paper describes in detail how BOMs and Modular FOMs can be used together for optimal reuse and interoperability from the early modeling stages to the final integration and execution phases.

Authors: Björn Möller, Paul Gustavson, Bob Lutz, Björn Löfstrand
Publication: Proceedings of 2007 Fall Simulation Interoperability Workshop, 07F-SIW-069, Simulation Interoperability Standards Organization, September 2007.

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Use Cases for the HLA Evolved Modular FOMs

ABSTRACT: The HLA Federation Object Model (FOM) describes the information that is to be exchanged during the execution of a federation. In earlier versions of HLA a federation had one monolithic FOM. HLA Evolved (the next version of HLA) introduces Modular FOMs which allow a federation to load FOM data as modules and to extend the FOM during the execution.

The modular approach to FOMs introduces many new opportunities and use cases:
Modular development of reference FOMs. Reference FOMs are very important for the reuse of federates. One example is the multitude of COTS and project specific RPR FOM based federates. They enable commercial and government users of M&S to quickly compose federations to meet their needs with low risk and at a modest cost. At the same time the sheer size of such FOMs, that may cover many aspects of the simulation, makes the development slow and costly. Modular FOMs can make this process quicker, more flexible and less costly.

Efficient handling of specialized extensions of reference FOMs. Reference FOMs are frequently modified and extended to support the simulation of local or specialized entities or services. This has resulted in a large number of uncorrelated versions of reference FOMs. As M&S users need to interoperate between sites, services and nations the handling of these non-standard versions of reference FOMs introduces risk and cost. Modular FOMs can separate out particular concerns thus preserving the reusability through reference FOMs and keeping the extension process
well-controlled.

Reusable federation agreements modules. For particular aspects of a federation, it will now be possible to provide a FOM module and a corresponding federation agreement. This may be a smaller aspect, like start and stop signaling or time pacing, or larger aspects like voice communications or weather services. In this way modular FOMs can support reuse of components of simulations systems across and between federations.

Support for long-running, GIG-style federations. Today’s HLA federations require the entire FOM to be loaded upon startup. In many larger systems, new capabilities need to be added over time without shutting down the entire federation. Modular FOMs allow new capabilities to be loaded when federates supporting these new capabilities join at a later point in time.

Authors: Björn Möller, Björn Löfstrand
Publication: Proceedings of 2007 Euro Simulation Interoperability Workshop, 07E-SIW-040, Simulation Interoperability Standards Organization, June 2007.

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An Overview of the HLA Evolved Modular FOMs

ABSTRACT: The HLA Federation Object Model (FOM) describes the information that is to be exchanged during the execution of a federation. When the federation execution is created, the RTI loads the FOM. This enables the participating federates to refer to the object model, for example when publishing and subscribing to information.

As in many other cases, a monolithic architecture restricts the speed, flexibility, and accuracy of the development process which in turn affects the resulting FOM. As part of HLA Evolved the concept of FOM modules have been added. The FOM is thus broken down into composable modules that can build upon each other. This allows a subset of federates to specify what data they need to exchange upon joining, in addition to the initially loaded FOM.

The main advantage is the increased flexibility during runtime and, not the least, during the development process. Federation developers can build new modules that extend reference FOMs without modifying them. Reference FOMs can be developed by several smaller communities in different domains or for different local or national extensions. Temporary additions will not result in a multitude of similar FOMs.

It will also now be possible to have long-running or persistent federations in virtual arenas where new capabilities and types of shared information can be added over time.

The modular FOMs are expected to revitalize a long needed development of shared information models. This is an important and necessary next step towards even higher degrees of interoperability that build on top of the High Level Architecture.

Authors: Björn Möller, Björn Löfstrand, Mikael Karlsson
Publication: Proceedings of 2007 Spring Simulation Interoperability Workshop, 07S-SIW-108, Simulation Interoperability Standards Organization, March 2007. 

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Developing Web Centric Federates and Federations using the HLA Evolved Web Services API

ABSTRACT: The new Web Services API of HLA Evolved offers several new opportunities for federation developers, both from an architectural and a programming perspective. This paper provides an introduction and a number of recommended practices for federation designers and federate programmers, including some references to FEDEP.

The first and maybe most important step is to take a web-centric approach to the overall federation design. This includes deciding upon how the federation is to be provided as a service. How will executions and potential
participants be managed and how will authentication take place. When are federates allowed to join? Performance characteristics and fault tolerance need to be taken into considerations. It also includes determining reasonable update and interactions rates based on the expected available bandwidth. This in turn may introduce the need for deadreckoning
and similar methods.

The next step is to set up a productive development and debugging environment. A wide array of code generation and WSDL analysis tools are available. An RTI with a Web Service Provider component that follows the HLA WSDL standard is of course also needed.

When developing web services federates, some features may require special attention, including:

  • Connection and authentication
  • Session handling, time-outs and fault tolerance
  • Bandwidth management and tuning
  • Use of handles
  • Data encoding and time representation
  • Callback delivery
  • Support services
  • Long-haul deployment

    Finally the pros and cons of Web Services based federates versus C++ and Java API federates are discussed.

Authors: Björn Möller, Clarence Dahlin, Mikael Karlsson
Publication: Proceedings of 2007 Spring Simulation Interoperability Workshop, 07S-SIW-107, Simulation Interoperability Standards Organization, March 2007.

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A Management Overview of the HLA Evolved Web Service API

ABSTRACT: A new API has been added to the HLA IEEE 1516 standard for simulation interoperability. The new API is based on Web Services, an implementation of the Service Oriented Architecture. This paper provides an overview from a strategic and architectural viewpoint targeted at program and project managers as well as technology
strategists.

The capabilities of HLA and Web Services may at first seem to overlap. A closer look reveals some fundamental
differences:

  • Web Services provides a loosely coupled mechanism for performing coarse-grained services with modest performance over both LAN and WAN. Services are supposed to be stateless and context independent. It is based on technologies that are familiar to most enterprises. A wide range of supporting vendors and software is available.
  • HLA provides extremely high performance and scalability for interactions and information exchange in a shared, complex state. It also provides unique capabilities for synchronizing the data exchange between systems using logical time, as opposed to wall clock time.

    The Web Service API for HLA combines the best of these two worlds, bringing the above capabilities to a shared approach.

    Major benefits of the WSDL API include the support for numerous newer and older languages and operating systems as well as the ease of deployment across wide area networks. Major limitations are performance and scalability.

    The major long term benefit of the WSDL API is that it promotes and supports the concept of simulations as readily available services provided within and between enterprises.

Authors: Björn Möller, Staffan Löf
Publication: Proceedings of 2006 Fall Simulation Interoperability Workshop, 06F-SIW-024, Simulation Interoperability Standards Organization, September 2006.

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Pathfinder Integration Environment –Knowledge and Resources Documentation Enabling Efficient Reuse

ABSTRACT: The NATO Modeling and Simulation Group (NMSG) under the Research and Technology Organization (RTO) has the mission to provide readily available, flexible and cost-effective means to enhance NATO operations and the vision to promote co-operation among Alliance bodies, NATO Member Nations and Partnership-for- Peace (PfP) Nations to maximize the effective utilization of M&S. NMSG is responsible for the Pathfinder program, which guides various technical activities conducted by NMSG expert groups. The Pathfinder Integration Environment (PIE) is currently defined and implemented under leadership of Technical Activity MSG-027. Part of this activity is the prototypical implementation of the Pathfinder Web Portal.

This paper presents the Web Portal in the context of MSG-027 and the Pathfinder program. The potential standards for describing M&S Resources and Knowledge for efficient reuse are the main focus of the paper.

Authors: NATO MSG-027 prepared by Andreas Tolk, presented by Björn Löfstrand
Publication: Proceedings of 2005 Euro Simulation Interoperability Workshop, 06E-SIW-007, Simulation Interoperability Standards Organization, June 2006.

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A First Look at the HLA Evolved Web Service API

ABSTRACT: A new API is being added to the IEEE 1516 HLA standard for simulation interoperability. The new API is based on Web Services, an implementation of the Service Oriented Architecture. This paper provides a brief technical introduction and an overview from a strategic and architectural viewpoint.

A Web Service is a service that can be accessed from another system using an http request and response, similar to fetching a web page. The request and response is described using XML. A service can be described using the Web Service Description Language (WSDL). This is currently the predominant implementation of the Service Oriented Architecture.

The capabilities of HLA and Web Services may at first seem to overlap. A closer look reveals some fundamental differences:

  • Web Services provides a loosely coupled mechanism for performing coarse-grained services with modest performance over both LAN and WAN. Services are supposed to be stateless. It is based on technologies that are familiar to most enterprises. A wide range of supporting vendors and software is available.
  • HLA provides extremely high performance and scalability for interactions and information exchange in a shared, complex state (scenario). It also provides unique capabilities for synchronizing the data exchange between systems using scenario time (as opposed to wall clock time).

    The Web Service API for HLA combines the best of these two worlds, bringing the above capabilities to a shared approach. Simulation system functionality may now be accessed in three ways:
  • Web Services systems can access the functionality of a federation on a coarse-grained service level using Web Services.
  • Web Services systems that need a closer interaction, synchronization and more efficient access to the shard scenario can use the HLA Web Service API to fully participate as federates in the federation.
  • Federates requiring the highest level of performance and scalability can use the C++ or Java API.

    The Web Service API will allow simulation developers to reap the benefits of both the Web Service and the HLA technologies. As the Service Oriented Architecture evolves beyond the current http and request-response implementation these two technologies can be expected to blend, potentially into new concepts and interoperability
    architectures.

Authors: Björn Möller, Clarence Dahlin
Publication: Proceedings of 2005 Euro Simulation Interoperability Workshop, 06E-SIW-061, Simulation Interoperability Standards Organization, June 2006.

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