<s>
The	O
Aggregate	B-Operating_System
Level	I-Operating_System
Simulation	I-Operating_System
Protocol	I-Operating_System
(	O
ALSP	B-Operating_System
)	O
is	O
a	O
protocol	O
and	O
supporting	O
software	O
that	O
enables	O
simulations	O
to	O
interoperate	O
with	O
one	O
another	O
.	O
</s>
<s>
Replaced	O
by	O
the	O
High	B-Operating_System
Level	I-Operating_System
Architecture	I-Operating_System
(	O
simulation	O
)	O
(	O
HLA	O
)	O
,	O
it	O
was	O
used	O
by	O
the	O
US	O
military	O
to	O
link	O
analytic	O
and	O
training	O
simulations	O
.	O
</s>
<s>
ALSP	B-Operating_System
consists	O
of	O
:	O
</s>
<s>
ALSP	B-Operating_System
Infrastructure	O
Software	O
(	O
AIS	O
)	O
that	O
provides	O
distributed	O
runtime	O
simulation	O
support	O
and	O
management	O
;	O
</s>
<s>
Participating	O
simulations	O
adapted	O
for	O
use	O
with	O
ALSP	B-Operating_System
.	O
</s>
<s>
In	O
1990	O
,	O
the	O
Defense	O
Advanced	O
Research	O
Projects	O
Agency	O
(	O
DARPA	O
)	O
employed	O
The	O
MITRE	O
Corporation	O
to	O
study	O
the	O
application	O
of	O
distributed	O
interactive	O
simulation	O
principles	O
employed	O
in	O
SIMNET	B-General_Concept
to	O
aggregate-level	O
constructive	O
training	O
simulations	O
.	O
</s>
<s>
Based	O
on	O
prototype	O
efforts	O
,	O
a	O
community-based	O
experiment	O
was	O
conducted	O
in	O
1991	O
to	O
extend	O
SIMNET	B-General_Concept
to	O
link	O
the	O
US	O
Army	O
's	O
and	O
the	O
US	O
Air	O
Force	O
's	O
.	O
</s>
<s>
The	O
first	O
ALSP	B-Operating_System
confederation	O
,	O
providing	O
air-ground	O
interactions	O
between	O
CBS	O
and	O
AWSIM	O
,	O
supported	O
three	O
major	O
exercises	O
in	O
1992	O
.	O
</s>
<s>
By	O
1995	O
,	O
ALSP	B-Operating_System
had	O
transitioned	O
to	O
a	O
multi-Service	O
program	O
with	O
simulations	O
representing	O
the	O
US	O
Army	O
(	O
CBS	O
)	O
,	O
the	O
US	O
Air	O
Force	O
(	O
AWSIM	O
)	O
,	O
the	O
US	O
Navy	O
(	O
RESA	O
)	O
,	O
the	O
US	O
Marine	O
Corps	O
(	O
)	O
,	O
electronic	O
warfare	O
(	O
JECEWSI	O
)	O
,	O
logistics	O
(	O
CSSTSS	O
)	O
,	O
and	O
intelligence	O
(	O
)	O
.	O
</s>
<s>
ALSP	B-Operating_System
developed	O
and	O
demonstrated	O
key	O
aspects	O
of	O
distributed	O
simulation	O
,	O
many	O
of	O
which	O
were	O
applied	O
in	O
the	O
development	O
of	O
HLA	O
.	O
</s>
<s>
An	O
architecture	O
that	O
permits	O
simulations	O
to	O
continue	O
to	O
use	O
their	O
existing	O
architectures	O
while	O
participating	O
in	O
an	O
ALSP	B-Operating_System
confederation	O
.	O
</s>
<s>
DARPA	O
was	O
funding	O
development	O
of	O
a	O
distributed	O
tank	O
trainer	O
system	O
called	O
SIMNET	B-General_Concept
where	O
individual	O
,	O
computerized	O
,	O
tank-crew	O
trainers	O
were	O
connected	O
over	O
local	O
area	O
networks	O
and	O
the	O
DSI	O
to	O
cooperate	O
in	O
a	O
single	O
,	O
virtual	O
battlefield	O
.	O
</s>
<s>
The	O
success	O
of	O
SIMNET	B-General_Concept
,	O
the	O
disappointment	O
of	O
ACE-89	O
,	O
and	O
the	O
desire	O
to	O
combine	O
existing	O
combat	O
simulations	O
prompted	O
DARPA	O
to	O
initiate	O
research	O
that	O
lead	O
to	O
ALSP	B-Operating_System
.	O
</s>
<s>
Despite	O
representational	O
differences	O
,	O
several	O
principles	O
of	O
SIMNET	B-General_Concept
applied	O
to	O
aggregate-level	O
simulations	O
:	O
</s>
<s>
The	O
ALSP	B-Operating_System
challenge	O
had	O
requirements	O
beyond	O
those	O
of	O
SIMNET	B-General_Concept
:	O
</s>
<s>
The	O
architecture	O
implied	O
by	O
ALSP	B-Operating_System
must	O
be	O
unobtrusive	O
to	O
existing	O
architectures	O
.	O
</s>
<s>
A	O
conceptual	B-Application
framework	I-Application
is	O
an	O
organizing	O
structure	O
of	O
concepts	O
that	O
facilitates	O
simulation	O
model	O
development	O
.	O
</s>
<s>
The	O
ALSP	B-Operating_System
conceptual	B-Application
framework	I-Application
is	O
object-based	O
where	O
a	O
model	O
is	O
composed	O
of	O
objects	O
that	O
are	O
characterized	O
by	O
attributes	O
to	O
which	O
values	O
are	O
assigned	O
.	O
</s>
<s>
ALSP	B-Operating_System
supports	O
a	O
confederation	O
of	O
simulations	O
that	O
coordinate	O
using	O
a	O
common	O
model	O
.	O
</s>
<s>
Because	O
of	O
an	O
underlying	O
requirement	O
for	O
scalability	O
,	O
the	O
ALSP	B-Operating_System
design	O
adopted	O
the	O
second	O
strategy	O
.	O
</s>
<s>
ALSP	B-Operating_System
prescribes	O
that	O
each	O
simulation	O
maps	O
between	O
the	O
representational	O
scheme	O
of	O
the	O
confederation	O
and	O
its	O
own	O
representational	O
scheme	O
.	O
</s>
<s>
This	O
mapping	O
represents	O
one	O
of	O
the	O
three	O
ways	O
in	O
which	O
a	O
simulation	O
must	O
be	O
altered	O
to	O
participate	O
in	O
an	O
ALSP	B-Operating_System
confederation	O
.	O
</s>
<s>
In	O
the	O
parlance	O
of	O
ALSP	B-Operating_System
,	O
this	O
is	O
an	O
interaction	O
.	O
</s>
<s>
The	O
object-based	O
conceptual	B-Application
framework	I-Application
adopted	O
by	O
ALSP	B-Operating_System
defines	O
classes	O
of	O
information	O
that	O
must	O
be	O
distributed	O
.	O
</s>
<s>
The	O
ALSP	B-Operating_System
Infrastructure	O
Software	O
(	O
AIS	O
)	O
provides	O
data	O
distribution	O
and	O
process	O
coordination	O
.	O
</s>
<s>
Principal	O
components	O
of	O
AIS	O
are	O
the	O
ALSP	B-Operating_System
Common	O
Module	O
(	O
ACM	O
)	O
and	O
the	O
ALSP	B-Operating_System
Broadcast	O
Emulator	O
(	O
ABE	O
)	O
.	O
</s>
<s>
The	O
ALSP	B-Operating_System
Common	O
Module	O
(	O
ACM	O
)	O
provides	O
a	O
common	O
interface	O
for	O
all	O
simulations	O
and	O
contains	O
the	O
essential	O
functionality	O
for	O
ALSP	B-Operating_System
.	O
</s>
<s>
ALSP	B-Operating_System
time	O
management	O
facilities	O
support	O
discrete	O
event	O
simulation	O
using	O
either	O
asynchronous	O
(	O
next-event	O
)	O
or	O
synchronous	O
(	O
time-stepped	O
)	O
time	O
advance	O
mechanisms	O
.	O
</s>
<s>
An	O
ALSP	B-Operating_System
Broadcast	O
Emulator	O
(	O
ABE	O
)	O
facilitates	O
the	O
distribution	O
of	O
ALSP	B-Operating_System
information	O
.	O
</s>
<s>
This	O
permits	O
configurations	O
where	O
all	O
ALSP	B-Operating_System
components	O
are	O
local	O
to	O
one	O
another	O
(	O
on	O
the	O
same	O
computer	O
or	O
on	O
a	O
local	O
area	O
network	O
)	O
.	O
</s>
<s>
The	O
ALSP	B-Operating_System
communication	O
scheme	O
consists	O
of	O
(	O
1	O
)	O
an	O
inter-component	O
communications	O
model	O
that	O
defines	O
the	O
transport	O
layer	O
interface	O
that	O
connects	O
ALSP	B-Operating_System
components	O
,	O
(	O
2	O
)	O
a	O
layered	O
protocol	O
for	O
simulation-to-simulation	O
communication	O
,	O
object	O
management	O
,	O
and	O
time	O
management	O
,	O
(	O
3	O
)	O
a	O
message	O
filtering	O
scheme	O
to	O
define	O
the	O
information	O
of	O
interest	O
to	O
a	O
simulation	O
,	O
and	O
(	O
4	O
)	O
a	O
mechanism	O
for	O
intelligent	O
message	O
distribution	O
.	O
</s>
<s>
The	O
ALSP	B-Operating_System
protocol	O
is	O
based	O
on	O
a	O
set	O
of	O
orthogonal	O
issues	O
that	O
comprise	O
ALSP	B-Operating_System
's	O
problem	O
space	O
:	O
simulation-to-simulation	O
communication	O
,	O
object	O
management	O
,	O
and	O
time	O
management	O
.	O
</s>
<s>
The	O
simulation	O
protocol	O
is	O
the	O
main	O
level	O
of	O
the	O
ALSP	B-Operating_System
protocol	O
.	O
</s>
<s>
Objects	O
in	O
ALSP	B-Operating_System
are	O
defined	O
by	O
a	O
unique	O
id	O
number	O
,	O
a	O
class	O
,	O
and	O
a	O
set	O
of	O
attributes	O
associated	O
with	O
a	O
c1ass	O
.	O
</s>
<s>
It	O
is	O
defined	O
by	O
an	O
LALR( 1 )	O
context-free	O
grammar	O
.	O
</s>
<s>
The	O
object	B-General_Concept
manager	I-General_Concept
in	O
the	O
ACM	O
manages	O
the	O
objects	O
and	O
object	O
attributes	O
of	O
the	O
owned	O
and	O
ghosted	O
objects	O
known	O
to	O
the	O
ACM	O
.	O
</s>
<s>
To	O
minimize	O
message	O
traffic	O
between	O
components	O
in	O
an	O
ALSP	B-Operating_System
confederation	O
,	O
AIS	O
employs	O
a	O
form	O
of	O
intelligent	O
message	O
routing	O
that	O
uses	O
the	O
Event	O
Distribution	O
Protocol	O
(	O
EDP	O
)	O
.	O
</s>
