<s>
The	O
High	B-Operating_System
Level	I-Operating_System
Architecture	I-Operating_System
(	O
HLA	O
)	O
is	O
a	O
standard	O
for	O
distributed	O
simulation	O
,	O
used	O
when	O
building	O
a	O
simulation	O
for	O
a	O
larger	O
purpose	O
by	O
combining	O
(	O
federating	O
)	O
several	O
simulations	O
.	O
</s>
<s>
It	O
is	O
a	O
recommended	O
standard	O
within	O
NATO	O
through	O
STANAG	B-Operating_System
4603	I-Operating_System
.	O
</s>
<s>
A	O
Run-time	B-Application
Infrastructure	I-Application
(	O
RTI	O
)	O
that	O
provides	O
a	O
standardized	O
set	O
of	O
services	O
through	O
different	O
programming	O
languages	O
.	O
</s>
<s>
The	O
services	O
are	O
provided	O
as	O
C++	B-Language
and	O
Java	B-Language
APIs	B-General_Concept
as	O
well	O
as	O
Web	O
Services	O
.	O
</s>
<s>
In	O
1995	O
DMSO	O
formulated	O
a	O
vision	O
for	O
modeling	O
and	O
simulation	O
and	O
established	O
a	O
modeling	O
and	O
simulation	O
masterplan	O
,	O
which	O
included	O
the	O
High	B-Operating_System
Level	I-Operating_System
Architecture	I-Operating_System
.	O
</s>
<s>
Two	O
protocols	O
for	O
M&S	O
interoperability	O
already	O
existed	O
:	O
Distributed	B-Operating_System
Interactive	I-Operating_System
Simulation	I-Operating_System
(	O
DIS	O
)	O
,	O
focusing	O
on	O
real-time	O
platform	O
level	O
simulation	O
with	O
a	O
fixed	O
object	O
model	O
,	O
and	O
Aggregate	B-Operating_System
Level	I-Operating_System
Simulation	I-Operating_System
Protocol	I-Operating_System
(	O
ALSP	B-Operating_System
)	O
focusing	O
on	O
simulation	O
of	O
aggregate	O
with	O
time	O
management	O
,	O
ownership	O
management	O
and	O
flexible	O
object	O
models	O
,	O
called	O
confederation	O
models	O
.	O
</s>
<s>
To	O
facilitate	O
the	O
migration	O
for	O
DIS	O
users	O
,	O
a	O
Federation	O
Object	O
Model	O
corresponding	O
to	O
the	O
fixed	O
object	O
model	O
of	O
DIS	O
was	O
also	O
developed	O
as	O
the	O
Real-time	O
Platform	O
Reference	O
FOM	O
(	O
RPR	B-Operating_System
FOM	I-Operating_System
)	O
.	O
</s>
<s>
IEEE	O
1516.3-2003	O
–	O
Recommended	O
Practice	O
for	O
High	B-Operating_System
Level	I-Operating_System
Architecture	I-Operating_System
Federation	O
Development	O
and	O
Execution	O
Process	O
(	O
FEDEP	O
)	O
.	O
</s>
<s>
It	O
was	O
soon	O
found	O
that	O
the	O
1516-2000	O
standard	O
had	O
APIs	B-General_Concept
that	O
were	O
slightly	O
different	O
for	O
each	O
RTI	O
implementation	O
.	O
</s>
<s>
SISO	O
produced	O
a	O
standard	O
with	O
alternate	O
,	O
dynamic	O
link	O
compatible	O
(	O
DLC	O
)	O
C++	B-Language
and	O
Java	B-Language
APIs	B-General_Concept
:	O
</s>
<s>
The	O
DLC	O
APIs	B-General_Concept
were	O
later	O
merged	O
into	O
the	O
main	O
standard	O
.	O
</s>
<s>
Major	O
improvements	O
in	O
IEEE	O
1516-2010	O
include	O
Modular	O
FOMs	O
,	O
incorporation	O
of	O
the	O
DLC	O
APIs	B-General_Concept
in	O
C++	B-Language
and	O
Java	B-Language
,	O
a	O
Web	O
Services	O
API	B-General_Concept
and	O
Fault	O
Tolerance	O
.	O
</s>
<s>
Machine-readable	O
parts	O
of	O
this	O
version	O
of	O
HLA	O
,	O
such	O
as	O
XML	O
Schemas	O
,	O
C++	B-Language
,	O
Java	B-Language
and	O
WSDL	O
APIs	B-General_Concept
as	O
well	O
as	O
FOM/SOM	O
samples	O
can	O
be	O
downloaded	O
from	O
.	O
</s>
<s>
The	O
services	O
are	O
provided	O
as	O
C++	B-Language
and	O
Java	B-Language
APIs	B-General_Concept
as	O
well	O
as	O
Web	O
Services	O
.	O
</s>
<s>
Run-time	B-Application
Infrastructure	I-Application
(	O
RTI	O
)	O
:	O
Software	O
that	O
provides	O
a	O
standardized	O
set	O
of	O
services	O
,	O
as	O
specified	O
in	O
the	O
HLA	O
Federate	O
Interface	O
Specification	O
.	O
</s>
<s>
Services	O
are	O
provided	O
through	O
a	O
C++	B-Language
or	O
Java	B-Language
API	B-General_Concept
and	O
also	O
using	O
Web	O
services	O
.	O
</s>
<s>
In	O
the	O
C++	B-Language
and	O
Java	B-Language
APIs	B-General_Concept
,	O
services	O
are	O
invoked	O
using	O
calls	O
to	O
an	O
instance	O
of	O
the	O
RTI	O
Ambassador	O
class	O
.	O
</s>
<s>
In	O
the	O
Web	O
Services	O
API	B-General_Concept
,	O
defined	O
using	O
WSDL	O
,	O
calls	O
are	O
made	O
,	O
and	O
callbacks	O
are	O
fetched	O
,	O
by	O
the	O
federate	O
using	O
Web	O
Services	O
requests	O
and	O
responses	O
.	O
</s>
<s>
In	O
a	O
federation	O
,	O
all	O
representation	O
of	O
objects	O
in	O
the	O
FOM	O
shall	O
be	O
in	O
the	O
federates	O
,	O
not	O
in	O
the	O
run-time	B-Application
infrastructure	I-Application
(	O
RTI	O
)	O
.	O
</s>
<s>
During	O
a	O
federation	O
execution	O
,	O
federates	O
shall	O
interact	O
with	O
the	O
run-time	B-Application
infrastructure	I-Application
(	O
RTI	O
)	O
in	O
accordance	O
with	O
the	O
HLA	O
interface	O
specification	O
.	O
</s>
<s>
The	O
IEEE	B-Operating_System
1516	I-Operating_System
standard	O
has	O
been	O
revised	O
under	O
the	O
SISO	O
HLA-Evolved	O
Product	O
Development	O
Group	O
and	O
was	O
approved	O
25-Mar-2010	O
by	O
the	O
IEEE	O
Standards	O
Activities	O
Board	O
.	O
</s>
<s>
The	O
revised	O
IEEE	B-Operating_System
1516	I-Operating_System
–	O
2010	O
standard	O
includes	O
current	O
DoD	O
standard	O
interpretations	O
and	O
the	O
EDLC	O
API	B-General_Concept
,	O
an	O
extended	O
version	O
of	O
the	O
SISO	O
DLC	O
API	B-General_Concept
.	O
</s>
<s>
HLA	O
(	O
in	O
both	O
the	O
current	O
IEEE	B-Operating_System
1516	I-Operating_System
version	O
and	O
its	O
ancestor	O
"	O
1.3	O
"	O
version	O
)	O
is	O
the	O
subject	O
of	O
the	O
NATO	O
standardization	O
agreement	O
(	O
STANAG	B-Operating_System
4603	I-Operating_System
)	O
for	O
modeling	O
and	O
simulation	O
:	O
Modeling	O
And	O
Simulation	O
Architecture	O
Standards	O
For	O
Technical	O
Interoperability	O
:	O
High	B-Operating_System
Level	I-Operating_System
Architecture	I-Operating_System
(	O
HLA	O
)	O
.	O
</s>
<s>
In	O
regards	O
to	O
the	O
Distributed	O
Modeling	O
and	O
Simulation	O
(	O
DM&S	O
)	O
industry	O
the	O
most	O
often	O
used	O
alternative	O
to	O
the	O
HLA	O
,	O
for	O
real-time	O
simulation	O
of	O
military	O
platforms	O
,	O
is	O
Distributed	B-Operating_System
Interactive	I-Operating_System
Simulation	I-Operating_System
(	O
DIS	O
)	O
,	O
IEEE	O
1278.1-2012	O
,	O
a	O
simulation	O
protocol	O
.	O
</s>
<s>
Most	O
HLA	B-Application
RTI	I-Application
vendors	I-Application
also	O
feature	O
DIS	O
in	O
their	O
products	O
.	O
</s>
<s>
the	O
publish	O
and	O
subscribe	O
feature	O
(	O
P&S	O
)	O
see	O
Data	B-Application
Distribution	I-Application
Service	I-Application
(	O
DDS	O
)	O
which	O
shares	O
many	O
of	O
the	O
same	O
characteristics	O
but	O
having	O
an	O
open	O
on-the-wire	O
protocol	O
for	O
system	O
interoperability	O
.	O
</s>
<s>
HLA	O
is	O
a	O
Message-oriented	B-Application
middleware	I-Application
that	O
defines	O
as	O
a	O
set	O
of	O
services	O
,	O
provided	O
by	O
a	O
C++	B-Language
or	O
Java	B-Language
API	B-General_Concept
.	O
</s>
