A Distributed Simulation Standard:High Level Architecture (HLA)(Part 8)Dr.Çağatay ÜNDEĞER
Öğretim Görevlisi
Bilkent Üniversitesi Bilgisayar Mühendisliği Bölümü

e-mail : cagatay@undeger.com
cagatay@cs.bilkent.edu.tr

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Bilgisayar Mühendisliği Bölümü – Bilkent Üniversitesi – Fall 2008

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A Distributed Simulation Standard:High Level Architecture (HLA)(Outline)•••

Introduction to Distributed Simulations
Introduction to HLAHLA Interface Specification:– Federation Management– Declaration Management– Object Management• Conclusion
CS-50321Distributed Simulation• An integrated simulation that is partitioned into anumber of smaller simulations over different
computational units (e.g. processors, computers).
• Provides higher scalability and multi userinteraction.
• A system, whose performance improves
proportional to the computational capacity added,
is said to be a scalable system.

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Distributed Simulation
Constructive

Live

Deployment region:
From One room toEntire world

VirtualVirtualLive

Constructive
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High Level Architecture(HLA)• An IEEE (1516) Distributed Modeling & Simulation
Standard• Developed By DMSO– Current technology was not providing tools
necessary to achieve DoD M&S Master Plan.
– A Standard was Needed For the Interoperabilityof Developed Simulations.

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What is HLA?
• A service that provides:– Major functional elements,– Interfaces,– Design rules,– A common framework for communicationof simulations.

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The Structure of HLA
Simulations(Federates)
Simulations
Simulations

Federation

Usually a Centralized Approach
All Simulations Communicate via RTI
RUN TIME INFRASTRUCTURE (RTI)• Federation Management• Declaration Management• Object Management• Ownership Management• Time Management• Data Distribution Management
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Defining the HLA• The HLA is composed of three elements:– HLA Rules:– A set of rules which must be followed to achieve
proper interaction of simulations in a federation– Interface Specification:• Definition of the interface functions between theRTI and the simulations subject to the HLA– Object Model Template (OMT):• The prescribed common method for recording
the information contained in the required HLA
Object Model for each federation andsimulation
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HLA Object Models
SOM: Simulation object model
FOM: Federation object model

SOM of Federate
e.g. A F14 Simulator
SOM of Federatee.g. A F16 Simulator

RTISOM of Federatee.g. Weapon TrajectoryManager
FOM of Federatione.g. A Flight simulation

OMT, documentationof the system, is saved
into a data storage
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HLA Rules• Federation Rules:– Federations shall have an HLA Federation Object Model (FOM),
documented in accordance with the HLA Object Model Template.
– In a federation, all representation of objects in the FOM shall be in
the federates, not in the runtime infrastructure (RTI).
– .....

• Federate Rules:– Federates shall have an HLA Simulation Object Model (SOM),
documented in accordance with the HLA Object Model Template.
– Federates shall be able to update and/or reflect any attributes ofobjects in their SOM and send and/or receive SOM object
interactions externally, as specified in their SOM.
– .....

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HLA Interface Specification
Category

Functionality

Federation Management

Create and delete federation executions
Join and resign federation executions
Control checkpoint, pause, resume, restart

Declaration Management

Establish intent to publish and subscribe
to object attributes and interactions

Object Management

Create and delete object instances
Control attribute and interaction publication
Create and delete object reflections

Ownership Management
Time Management
Data Distribution Management

Transfer ownership of object attributes
Coordinate the advance of logical timeand its relationship to real time
Supports efficient routing of data
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Federation Management• Federation management refers to thecreation, dynamic control, modification, anddeletion of a federation execution.

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Basic steps of federation execution126Federation Management

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Overview of Federate To RTI Relationship13

Federation Management(Initialization/Finalization of a Federate)• CreateFederationExecution• JoinFederationExecution

Initialization ofa federate• ...
• Normal federate execution....
• ...
• ResignFederationExecution• DestroyFederationExecution
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Finalization ofa federate
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Federation Management(Lifetime of a Federate)

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Declaration Management• Federates use Declaration Management
services to declare their intention;– To generate information, and– To receive information.
– A joined federate shall invoke appropriate
Declaration Management services• Before it may register object instances,
update instance attribute values, andsend interactions.
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Declaration Management• PublishObjectClass• UnpublishObjectClass

Declares which classes it isplanning to use in order tocreate object instances ofthese classes.

• SubscribeObjectClassAttributes• UnsubscribeObjectClass

Declares which classes (and their attributes) it is planning to use
in order to receive information of object instances of these classes.

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Object Management• Deals with;– The registration, modification, and deletionof object instances, and– The sending and receipt of interactions.
• Object instance discovery is the prime
concept in this service group.

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189Object Management• When a joined federate either;– Uses the Register Object Instance service
to register an object instance or– Receives an invocation of the DiscoverObject Instance to discover an objectinstance,• That object instance becomes known to thejoined federate.

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Object Management
Publishing Services
RegisterObjectInstance
UpdateAttributeValues
DeleteObjectInstance

Subscribing Services
DiscoverObjectInstance
ReflectAttributeValues
RemoveObjectInstance

RUN TIME INFRASTRUCTURE (RTI)
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Support Services• GetObjectClassHandle• All the classes defined inthe FOM has a uniquename and handle.
• This function returns thehandle given the name ofthe class.
e.g. “Aircraft.bomber.F15”• GetAttributeHandle• All the attributes ofclasses defined in the FOM
has a unique name andhandle.
• This function returns thehandle given the name of
the attribute.
e.g. “Aircraft.bomber.F15.x”
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Class Hierarchy andPublish/Subscribe Mechanism• Classes are defined as a hierarchy such as:– Aircraft [ Attributes: Type,X,Y,Z,H,P,R,V ]• Bomber [ Attributes: NumOfFullBombs ]– F15 [ Attributes: WingsOn ]• Fighter [ Attributes: NumOfFullRightPylons, ... ]– F14 [ Attributes: WingsOn, GearsOn ]– F16 [ Attributes: FiringGun ]• Federates can publish and/or subscribe to one ormore arbitrary classes and attributes on thehierarchy.
• RTI should filter the data and send to the federates
only what they are interested in.
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Example: Discovering
Instances
AircraftBomber

F15

subscribedFederate A

Fighter
F14

discovers
Fighter for
F16

published

F16
published

Federate B
discovers
Aircraft for
F15
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subscribedCS-503Federation Execution Data
File (FED File)(FED(Federation FederationName)(FEDversion v1.3)(spaces )(objects(class ObjectRoot(attribute privilegeToDelete reliable timestamp)(class RTIprivate)(class Aircraft(attribute X best_effort receive)(attribute Y best_effort receive)(attribute Z best_effort receive)(class Fighter(attribute NumOfFullRightPylons best_effort receive)(attribute NumOfFullLeftPylons best_effort receive)(class F16(attribute FiringGun best_effort receive))......

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FED file defines:
classes,
attributes of classes,
interactions,parameters of interactions,routing spaces,
dimensions of spaces,...

of a FOM

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Conclusion• COTS RTI implementations have aCentralized Architecture.
• If RTI fails,– Whole simulation will fail.
• If a federate fails,– The simulation continues unless a
synchonized timing approach is used.

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