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18.2.2
Grid-Enabled Approach
In the grid-enabled approach, grid (or Web) service interfaces are pro-
vided to enable HLA-based distributed simulations to be conducted in a
grid (or Web) environment. There are various forms of this approach. One
form is that a client federate communicates with a federate server using
grid (or Web) service communications and the federate server represent-
ing the client federate joins an HLA-based distributed simulation using a
vendor-specii c RTI. Another form is that different federations are exe-
cuted using a vendor-specii c RTI at their own local sites and grid service
interfaces are dei ned to enable communications between the federations
so that a larger federation community can be formed over the grid.
An example of this approach is the work done by the XMSF group [17] to
integrate simulations with other applications using Web services [18]. Web
service interfaces are provided for a particular simulation application so
that other applications on the Web can interact with the simulation appli-
cation. For example, a remote passive visualizer can periodically probe
the simulation progress and display it accordingly; when the progress
is not satisfactory, an army C4I (command, control, communications, com-
puters, and intelligence) system can send a command to the simulation
application for adjustment. The communications between the simulation
application and the other applications are through Web service invocations
while the communications inside the simulation application are through
a vendor-specii c RTI.
As another example of this approach, new Web service APIs have
recently been proposed for the HLA IEEE 1516 standard [19]. With the
Web service APIs, a client federate on the Web communicates with a Web
Service Provider RTI Component (WSPRC), through which the federate
joins a federation.
Zhu et al. [20] proposed a grid-based distributed simulation architecture
(GDSA), in which grid service interfaces are dei ned for a federation so
that multiple federations can be integrated through the dei ned interfaces.
This enables HLA-based distributed simulations to be carried out over the
grid. Xu and Peng developed a grid-based simulation service bus (SSB) [21],
through which a remote federate on the grid can join a local federation in
a LAN and multiple federations are able to exchange data over the grid.
This effort follows the grid-enabled approach.
In a simulation grid [12], RTI grid service components are deployed to
provide non-real-time communication services between federations and
thus enable HLA-based distributed simulations to be executed over the
grid. To run HLA-based distributed simulations on the grid, our group
proposed a federate-proxy-RTI-based framework [22]. Proxies are pro-
vided so that a remote federate on the grid is able to join a local federation
through grid service communications with a proxy. All proxies and local
federates reside in a LAN and communicate with each other through a
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