Re: Truth in Advertising Randy Saunders <a href="/index.htm?LOGON=A3%3Dind9805%26L%3DZ-ARCHIVE-SIW-CFI%26E%3Dquoted-printable%26P%3D125682%26B%3D--%26T%3Dtext%252Fhtml%3B%2520charset%3DUTF-8%26XSS%3D3%26header%3D1" target="_parent" >[log in to unmask]</a> <a href="/index.htm?LOGON=A3%3Dind9805%26L%3DZ-ARCHIVE-SIW-CFI%26E%3Dquoted-printable%26P%3D125682%26B%3D--%26T%3Dtext%252Fhtml%3B%2520charset%3DUTF-8%26XSS%3D3%26header%3D1" target="_parent" >[log in to unmask]</a>
At 11:43 +0000 5/4/98, Robert Howard x601 wrote:
>	If conformance to a SISO published RTI API is not sufficient to
>	guarantee compatibility with -any- RTI that also conforms to that
>	API, then what is the value of HLA?
>Perhaps I am being naive, but it seems that since there are no standards
>or even guidlines as to what the SOM should contain, and only the most
>limited constraints on the FOM, then RTI incompatibility will mean that
>HLA compliance will not contribute to interoperability.  It would seem
>that the limited benifits of publishing a SOM could be achieved more
>efficiently by simply publishing the global variable for each model /
>simulation unless RTI compatibility is assured.

Consider an example.  Two companies make 56K modems (=RTIs).  They both
use the same interface to your computer (=model), called a serial port
(=API).  However, they are not interoperable.  Your ISP (■deration)
needs to decide which modem (=RTI) to use.  Some ISPs (■derations)
offer increased flexibility, at increased cost (=$$), by supporting both
modems (=RTIs) using internal mechanisms.  This works fine for a while,
the competing approaches vie for market share.  Everything is fine as
long as 56K modems (=RTIs) are only used by laboratories or early
adopters (=HLA 1998).

However, there are a bunch of nasty people in the world who control how
much gets spent on networking (=modeling and simulation).  These folks
want value for their money, and two solutions which don't interoperate
are low value.  The nasties say "We're not buying either approach until
it will let me talk to everybody".  This puts the modem (=RTI) providers
in a pickel.  If they gain compatibility they will lose their primary
lock on the market.  The investors who paid for the modem (=RTI) to be
developed see their control of the marketplace diminish.  Eventually
all sides allow the CCITT Standards group (=SISO) to control the
evolution of modem standards (=HLA standards) to merge the competing
implementations together.  After much nashing of teeth, everybody gets
a rev to their modem (=RTI) which supports universal compatibility.
The world is a happy, interoperable, productive place (=HLA 2001).

As a member of the SAC, speaking for myself and not the SAC, I would
welcome the formation of a group to identify the requirements and
standardize the interface between RTIs, if there were folks to get the
job done.  Right now it looks like a big, hard job with a small team
interested in attacking it.  This won't work, we tried it on the DIS
Communications Architecture standard.  Far better to get at least one
RTI that works (and I mean: high performance + low overhead = "works").
Then we can see if there is a need for another RTI implementation, and
then we can see what's involved in making them interoperate.  I don't
see the benefit in making laboratory curiosities like RTI 1.3 work
with the production RTI (2.0).  That doesn't mean it isn't there, but
nobody has explained it to me.  I think we'll have a group that does
this RTI <=> RTI interface standards stuff, so if you think this problem
will go away I think you're mistaken.  However, I think that about
18 months from now that task will be meaningful and doable.  If there
is a proposal for something we could do now that could be accomplished
with the available volunteers, I'd like to see it.

/Randy Saunders
Raytheon Systems Company
+1 (248) 619-8321 :voice
+1 (248) 619-8416 :fax
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