High Level Architecture

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High Level Architecture

• Phuoc Nguyen

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HLA Benefits

• Provide a common communication protocol between
  applications
• A standardized architecture for all simulations
• Manage and distribute data across simulation
• Promote reusability

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Overview

• HLA Component Breakdown
• HLA Specification
• HLA As an architecture
• Time Synchronization

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Components

• HLA is broken down into RTI and Federates
• RTI and Federation communicates through objects
  and interaction
• A collection of Federates makes up a Federation
• Federations are connected through Gateway

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Federates and RTI
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RTI

• Data routing to only subscribed Federates
• Keep track of objects
• Not a repository of data
• Handle Federate join
• Handle late joiner

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FOM Object
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FOM Interaction
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HLA Specification

• A Federation must have a FOM specification
• All Object instances reside in federate not RTI
• All exchange of objects shall occur via RTI
• Object instance may be updated by at most one
  owner
• Individual Federate shall be responsible for its
  own local time

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Time Synchronization

• Ensure events are delivered in order
• Each Federate has a logical clock
• Multiple level of Time Synchronization
  implemented among federates

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Level of Time Management
Time-Regulating
True
False
Strictly Time-Synchronized Conservative and
Optimistic
Viewer or Federation Management Tool. Stays
synchronized to Federation, but generates No
events
True
Time-Constrained
Unconstrained operating With conservation
Federates, or Pacing federate
Externally synchronized Simulation No time
management from RTIs standpoint
False
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Events Ordering

• Time Stamp Order (TSO)
• Only time-regulating federates can send TSO
• Only time-constraint federates can receive TSO
• RTI will guarantee distribution of TSO in order
• No events shall be deliver to federate in its past

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Synchronize Mechanism

• Prevent deadlock
• The slowest federate could hold the entire
  Federation

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Look-ahead

• Federates send events at time greater then
  look-ahead value
• Federates are free to advance local clock within
  the look-ahead value
• Larger look-ahead value allows high level of
  parallelism
• Larger look-ahead also mean slow response time.

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RTI Regulate Time Advancement

• All federates will request for time advancement
• RTI responsible to synchronize time advancement

Time Advancing
Time Granted
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Time Advancement
Look ahead value
Logical Time
Logical Time
TAR
Grant
TAR
Grant
TAR
Grant
Wall Clock Time
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HLA as a Solution

• Common architecture
• Interchanging components/federation
• Drawback is the added overhead
• Not suited for real-time simulation due to delay
  in time synchronization

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Resources

• Creating computer simulation systems
• Dr. Federick Kuhl
• Dr. Richard Weatherly
• Dr. Judith Dahmann
• http//en.wikipedia.org/wiki/High_Level_Architectu
  re