Information Technology Reference
In-Depth Information
backs for the federate in its callback module. Both HLA 1.3 and HLA 1516
service interfaces are supported in two different LRC libraries. The LRC is
lightweight, so a federate can be run on resource-limited platforms such
as PDAs and cellphones. Most of the local RTI processing, such as those
related to DDM and TM, is ofl oaded to the LRI in a similar way as ofl oad-
ing it to network processors in [28], so the federate has more computation
time for its real simulation work. Since the callbacks are buffered by the
LRI, federate m igrat ion is simplii ed [29]. The migration protocol proposed
in [15] requires the source federate to l ush all messages pending delivery
and insert them in a queue. Then the queue is encoded and transferred to
the migration destination where it gets decoded. Additionally, a complex
algorithm is used in the protocol to prevent event loss. SOHR does not
have these problems when migrating federates. A source federate just
transfers the federate code and its status. The migrated federate can then
connect to the same LRI to fetch the buffered callbacks.
18.4
Detailed Design of SOHR
18.4.1
Local RTI Component
The LRC is a federate side library that implements the HLA service inter-
faces and makes legacy HLA-based federates work in SOHR. It simply
does the translation between the HLA standard interfaces and LIS grid
service invocations, so it is quite lightweight. Both HLA 1.3 and HLA 1516
service interfaces are supported in two different LRC libraries. When
referring to a specii c HLA service interface, its HLA 1.3 version is used
for the description in this chapter.
The major component in LRC is the RTIambassador class, which imple-
ments various HLA service interfaces such as createFederationExecution
and tick. The other components are supporting classes and exception
classes such as the SuppliedParameters class used in the sendInteraction
service and the InteractionParameterNotKnown class that dei nes a type
of exception thrown when an interaction parameter is not valid. The
RTIambassador class translates HLA service requests to corresponding
grid service invocations of the LIS, for example an RTIambassador.
A createFederationExecution request by the local federate will be trans-
lated to a createFederationExecutionOut grid service invocation of the LIS,
which will further contact the RTI index service to create a new federa-
tion. A pulling mechanism is used for callbacks to the local federate. When
the local federate requests for callbacks by calling the RTIambassador.tick
(or evoke multiple callbacks in HLA 1516) function, the LRC pulls call-
backs from the LRI by invoking the getCallbacks service of the LIS. If any
Search WWH ::
Custom Search