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<DIV><FONT face=Arial>Francois,</FONT></DIV>
<DIV> </DIV>
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<DIV style="FONT: 10pt arial">----- Original Message ----- </DIV>
<DIV
style="BACKGROUND: #e4e4e4; FONT: 10pt arial; font-color: black"><B>From:</B>
<A href="mailto:audet@NORTELNETWORKS.COM"
title=audet@NORTELNETWORKS.COM>Francois Audet</A> </DIV>
<DIV style="FONT: 10pt arial"><B>To:</B> <A
href="mailto:ITU-SG16@mailbag.cps.intel.com"
title=ITU-SG16@mailbag.cps.intel.com>ITU-SG16@mailbag.cps.intel.com</A> </DIV>
<DIV style="FONT: 10pt arial"><B>Sent:</B> Thursday, June 01, 2000 8:49
AM</DIV>
<DIV style="FONT: 10pt arial"><B>Subject:</B> Re: On TD26 - Fast TCS and M/S
negotiation in H.323v4</DIV>
<DIV><BR></DIV>
<P><FONT size=2>> Paul,</FONT> <BR><FONT size=2>> </FONT><BR><FONT
size=2>> We agreed at the Osaka meeting to allow a SETUP to contain both
the</FONT> <BR><FONT size=2>> fastStart and h245Control, but it has not
been officially </FONT><BR><FONT size=2>> approved by the</FONT> <BR><FONT
size=2>> ITU.</FONT> <BR><FONT size=2>> </FONT><BR><FONT size=2>> As
it stands right now, I don't think I can agree to include </FONT><BR><FONT
size=2>> it in H.323v4</FONT> <BR><FONT size=2>> on the grounds that it
breaks backward compatibility with </FONT><BR><FONT size=2>> V2-- I just
don't</FONT> <BR><FONT size=2>> see a clean solution here.</FONT> </P>
<P><FONT size=2>It doesn't "break" anything. The call will still
proceed.</FONT> </P></BLOCKQUOTE>
<P><FONT face=Arial>It does break things. If I have a version 2 endpoint
and you send it a SETUP message containing both an H.245 tunneled message and
fastStart, the SETUP UUIE is invalid. What will an endpoint do?
Endpoints may select either one or the other or both, but we have no way of
knowing. That is the problem. If we knew predictably what
was going to happen, I'd be OK with this change. Unfortunately,
we have no idea what the result will be for every vendors endpoint. </FONT></P>
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<P><FONT size=2>> I'm opening to hearing more suggestions, but as you
pointed </FONT><BR><FONT size=2>> out, there are</FONT> <BR><FONT
size=2>> two issues:</FONT> <BR><FONT size=2>> 1) H.323v2
states explicitly that it is illegal</FONT> </P>
<P><FONT size=2>There are a lot of things that changed from v2 to v4. That's
the role of </FONT><BR><FONT size=2>versions.</FONT> </P></BLOCKQUOTE>
<P><FONT face=Arial>Since this goes in the SETUP, we have no chance to make a
decision based on the version number. However, one possible alternative is
for H.323v4 devices to put H.245 tunneled messages into a different, new field
in SETUP in H.225.0v4. We could create a new field called "earlyH245"--
that would be a compatible way based on versioning. The called endpoint,
if it is V4 or higher, shall not ignore this field and shall process the H.245
messages in parallel to the fastStart. That I could live with.</FONT></P>
<P><FONT face=Arial>How about that approach?</FONT></P>
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<P><FONT size=2>> 2) There is no way to know what version to
destination EP is before</FONT> <BR><FONT
size=2>> sending this illegal message</FONT>
</P>
<P><FONT size=2>That would apply to any single change that we do on H.225.0
and H.245.</FONT> </P></BLOCKQUOTE>
<P><FONT face=Arial>It does not apply to newly created fields-- they are ignored
by endpoints that do not understand them. However, when you change the
meaning of an existing field or the behavior associated with a field, you
introduce backward compatibility problems.</FONT></P>
<P><FONT face=Arial>How about the approach I suggest above-- adding an
"earlyH245" field?</FONT></P>
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