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Building Parallel Time-Constrained HLA Federates: A Case Study with the Parsec Parallel Simulation Language

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Building Parallel Time-Constrained HLA Federates: A Case Study with the Parsec Parallel Simulation Language C. D. Pham R. L. Bagrodia Department of Computer Science – PowerPoint PPT presentation

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Title: Building Parallel Time-Constrained HLA Federates: A Case Study with the Parsec Parallel Simulation Language


1
Building Parallel Time-Constrained HLA Federates
A Case Study with the Parsec Parallel Simulation
Language
C. D. Pham R. L. Bagrodia Department of
Computer Science University of California, Los
Angeles
Winter Simulation Conference (WSC98), Washington
D.C. Tuesday, December 15th, 1998
2
Outline
Overview of HLA and Parallel simulation The
rational behind this work The Parsec Language
Architecture of a parallel federate with
Parsec Conclusions
3
The HLA framework
  • Without HLA, simulations are mostly independents
    and interoperability is not easy.
  • The High Level Architecture calls for a
    federation of simulations to achieve
    interoperability and reuse of software.

10 Rules for the federation and the federates
behavior
An Interface Specification
An Object Model Template to describe the
simulation objects
4
HLA How to interoperate?
communication node throughput, position
Objects can have attributes
radio transmitter power, frequency
wired node links
  • Interoperability is achieved by subscription and
    publication of objects attributes between the
    federates in the federation execution.

5
HLA Publication and Subscription
  • Publication of an attribute means a federate can
    produce values for that attribute.
  • Subscription to an attribute means a federate
    wishes to receive values for that attribute.

I can provide the position for F14 planes
I want to know the position of all F14 planes.
Federate
Federate Ambassador
Federate
Federate Ambassador
RTI Ambassador
RTI Ambassador
updateAttributeValues
RTI
6
HLA Time management
  • HLA includes advanced time management services
    with receive order and time stamped messages

7
Parallel Simulation Concepts
  • A model consists of simulation objects (logical
    processes) and events.
  • LPs are distributed on several processors.
  • Only time stamped events are exchanged between
    LPs.
  • Synchronization and causality constraints are
    handled by a conservative or optimistic
    simulation algorithm.

8
The rational behind this work
  • Parallel simulation can potentially reduce the
    simulation time of large scale systems.
  • HLA can benefit from parallel federates in a
    federation execution to achieve speed-up for the
    entire federation.

parallel computer NOWs...
9
Parallel simulation and HLA
HLA
PADS
Time management
  • As fast as possible execution.
  • Conservative or optimistic synchronization among
    LPs.
  • Mainly real time simulation.
  • Conservative among all the federates.

Interactions
  • Event paradigm.
  • In most cases, only time stamped events.
  • Subscription/publication.
  • Received Order and Time Stamped Order.

10
Parallel federates...
  • are time-constrained and time-regulated.
  • must take into account TSO messages from the RTI,
  • have to report a simulation time,
  • have to ask for time advance grants.
  • contain several logical processes.
  • have to compute a global simulation time,
  • provide non-blocking scheduling regarding time
    advance grants.

11
One or several federates?
Having several federates sometimes facilitates
the design of the model but introduces extra
dependencies in a conservative federates
It is better to have one federate for the entire
set of Logical Processes
12
Need for an accurate GST
  • Even a conservative federate has to implement a
    GST computation.
  • The GST is the only simulation time value the RTI
    knows about the parallel federate.
  • The GST must be computed frequently for the other
    federate to advance in time.

13
When and how to advance the time
  • LPs cannot request time advance grants directly
    from the RTI.
  • Messages from the RTI gain to be directly handled
    by the synchronization algorithm.
  • It is possible to use the LBTS from the RTI

14
The PARSEC language
Message-based, process-interaction approach
LP are programmed as an actor or entity all
activities of an entity are initiated on message
receipts An LP cannot directly modify the state
of another LP Event are represented by message
communications e(t,p,a) send message m(e) at
time t to LP p On receiving m(e), p executes
actions a change its state represented by local
variables schedule events (messages) at time
gtt LPs are scheduled with a large variety of
algorithms Conservative with null-messages,
conditional events, synchronous, optimistic and
adaptive algorithms.
15
Translation of notifications
  • Notifications from the RTI are translated into a
    PARSEC message and sent back to the entities.
  • Entities can register to receive a given set of
    notification types.

Ensure that both TSO and RO messages can be mixed
into PARSEC Ensure that the entities receive the
messages at the correct time
1
3
callback
RTI
2
has subscribed to c1.a1
has registered to reflect and discover
16
Time management support
Sequential federates
Entities interact directly with the RTI
HLA_timeAdvanceGrantRequest()
Request and wait for a time advance grant using
nextEventRequest.
RTI
17
Parallel federates
Entities interact with the RTI via a time manager
entity
Provides a simulation time value to the time
manager. Performs the GST computation and asks
for the time advance request from the RTI.
Indicates to the PARSEC runtime that an entity
wishes to participate in the GST computation.
Allocates data structures for the calling entity.
RTI
18
Overview of time management
Parallel federates
19
The wireless model example
  • 1 sequential federate a weather federate that
    publishes a weather_condition attribute.
  • 1 parallel federate a wireless communication
    network that subscribes to the weather_condition
    attribute.
  • The transmission quality depends on the
    weather_condition attribute.

Can the parallel federate provide speedup for
the entire federation execution?
20
Conclusions
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