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<DIV><SPAN class=559573920-16092003><FONT face=Arial color=#0000ff
size=2>Paul,</FONT></SPAN></DIV>
<DIV><SPAN class=559573920-16092003><FONT face=Arial color=#0000ff
size=2></FONT></SPAN> </DIV>
<DIV><SPAN class=559573920-16092003><FONT face=Arial color=#0000ff size=2>adding
TermCaps into the Setup in the future versions will not help, as none of
the existing applications, which might use V0 syntax, will put termCaps into the
Setup. </FONT></SPAN></DIV>
<DIV><SPAN class=559573920-16092003><FONT face=Arial color=#0000ff
size=2></FONT></SPAN><SPAN class=559573920-16092003><FONT face=Arial
color=#0000ff size=2></FONT></SPAN> </DIV>
<DIV><SPAN class=559573920-16092003><FONT face=Arial color=#0000ff
size=2>Anatoli</FONT></SPAN></DIV>
<BLOCKQUOTE dir=ltr style="MARGIN-RIGHT: 0px">
<DIV class=OutlookMessageHeader dir=ltr align=left><FONT face=Tahoma
size=2>-----Original Message-----<BR><B>From:</B> paulej@PACKETIZER.COM
[mailto:paulej@PACKETIZER.COM]<BR><B>Sent:</B> Tuesday, September 16, 2003
10:43 AM<BR><B>To:</B> itu-sg16@external.cisco.com<BR><B>Subject:</B> Re:
H.323 Fast Connect and Versioning<BR><BR></FONT></DIV>
<DIV><FONT face=Arial>Peter,</FONT></DIV>
<DIV><FONT face=Arial></FONT> </DIV>
<DIV><FONT face=Arial>To address there V0/V2 interop problem, I agree that
something like the syntax2002 would be useful. In fact, to answer your
question about other H.245 fields that are unknown to the other side... that's
precisely how things get quite naturally "dropped out" in the replies
back. It's an indicator to the originator.</FONT></DIV>
<DIV><FONT face=Arial></FONT> </DIV>
<DIV><FONT face=Arial>Looking past v2 to the subsequent revisions, what else
might change? Perhaps the syntax will remain unchanged or at least
compatible, but perhaps something else in the procedures might changes.
This is what I'm wondering if we should insert rules into H.323 (and Annex D
would be the candidate for fax) that says that you shall not accept a proposal
in Fast Connect for a version you do not support?</FONT></DIV>
<DIV><FONT face=Arial></FONT> </DIV>
<DIV><FONT face=Arial>The proper solution to this general problem, in my
opinion, is to advertise termcaps in the Setup (perhaps the
parallelH245Control field), along with Fast Connect, and then use either
H.460.6 to re-negotiate offered channels or use H.245 logical channel
signaling. There's certainly nothing wrong with not using Fast
Connect at all, but it seems to be quite popular and probably something I
would not want to disallow.</FONT></DIV>
<DIV><FONT face=Arial></FONT> </DIV>
<DIV><FONT face=Arial>Paul</FONT></DIV>
<DIV><FONT face=Arial></FONT> </DIV>
<BLOCKQUOTE dir=ltr
style="PADDING-RIGHT: 0px; PADDING-LEFT: 5px; MARGIN-LEFT: 5px; BORDER-LEFT: #000000 2px solid; MARGIN-RIGHT: 0px">
<DIV style="FONT: 10pt arial">----- Original Message ----- </DIV>
<DIV
style="BACKGROUND: #e4e4e4; FONT: 10pt arial; font-color: black"><B>From:</B>
<A title=PeterP@vegastream.com href="mailto:PeterP@vegastream.com">Peter
Price</A> </DIV>
<DIV style="FONT: 10pt arial"><B>To:</B> <A title=paulej@packetizer.com
href="mailto:paulej@packetizer.com">'Paul E. Jones'</A> ; <A
title=itu-sg16@external.cisco.com
href="mailto:itu-sg16@external.cisco.com">itu-sg16@external.cisco.com</A> ;
<A title=tsg16q14@itu.int
href="mailto:tsg16q14@itu.int">tsg16q14@itu.int</A> </DIV>
<DIV style="FONT: 10pt arial"><B>Sent:</B> Tuesday, September 16, 2003 5:00
AM</DIV>
<DIV style="FONT: 10pt arial"><B>Subject:</B> RE: H.323 Fast Connect and
Versioning</DIV>
<DIV><BR></DIV>
<DIV><FONT face=Arial color=#0000ff size=2><SPAN
class=120234207-16092003>Paul,</SPAN></FONT></DIV>
<DIV><FONT face=Arial color=#0000ff size=2><SPAN
class=120234207-16092003></SPAN></FONT> </DIV>
<DIV><FONT face=Arial color=#0000ff size=2><SPAN class=120234207-16092003>I
appreciate that Version 3, 4 etc don't exist yet but the issue we are
talking about here is a specific problem caused by an editorial error when
T.38 was first published that has resulted in an incompatible payload.
</SPAN></FONT><FONT face=Arial color=#0000ff size=2><SPAN
class=120234207-16092003>The problem is that if a V0/V1 endpoint
accepts a V2 offer it will not send a payload that is decodable by the V2
endpoint (and the V2 endpoint will send undecodable packets to the other
endpoint). T.38 is broken.</SPAN></FONT></DIV>
<DIV><FONT face=Arial color=#0000ff size=2><SPAN
class=120234207-16092003></SPAN></FONT> </DIV>
<DIV><FONT face=Arial color=#0000ff size=2><SPAN class=120234207-16092003>At
this stage we have to assume that such an incompatibility would be avoided
in future versions. If a future change to the standard resulted in a
new incompatibility with V2 then again it is effectively a new codec and
that future version would have to be protected in some way from V2 or older
versions. Since (nearly) all the fields are now extensible unless
someone decides we need a third error recovery mechanism it's hard to see
how T.38 can be broken again.</SPAN></FONT></DIV>
<DIV><FONT face=Arial color=#0000ff size=2><SPAN
class=120234207-16092003></SPAN></FONT> </DIV>
<DIV><FONT face=Arial color=#0000ff size=2><SPAN class=120234207-16092003>It
may well be that the Fast Connect rules should be reviewed but I do not
think this is the scenario that should drive the thinking. You say
that the video options can't be changed but what happens when your endpoint
doesn't understand them (ie can't decode them). What will the calling
endpoint do when it receives a response that has probably been
changed?</SPAN></FONT></DIV>
<DIV><FONT face=Arial color=#0000ff size=2><SPAN
class=120234207-16092003></SPAN></FONT> </DIV>
<DIV><FONT face=Arial color=#0000ff size=2><SPAN class=120234207-16092003>I
suspect that this changing of extended options will be the real issue in the
future as this will (should) be where differences between versions will
exist and any modifications to the Fast Connect rules can usefully address
this type of predictable issue. I still haven't seen any
response from video endpoint implementors who must have encountered this
scenario and must have views on how it should be handled. Maybe they
are not looking at this list and the question needs to be asked on the
implementors list.</SPAN></FONT></DIV>
<DIV><FONT face=Arial color=#0000ff size=2><SPAN
class=120234207-16092003></SPAN></FONT> </DIV>
<DIV><FONT size=+0><SPAN class=120234207-16092003>
<DIV><FONT face=Arial color=#0000ff size=2><SPAN
class=120234207-16092003>The T.38 problem does not fall into this category,
it is a result of an error in the standard and there is no way of of trying
to anticipate future problems caused by errors (and no point or gain).
The errors won't be the same (I hope) and will almost certainly require
unique solutions.</SPAN></FONT></DIV>
<DIV><FONT face=Arial color=#0000ff size=2><SPAN
class=120234207-16092003></SPAN></FONT> </DIV><SPAN
class=120234207-16092003>
<DIV><FONT face=Arial color=#0000ff size=2><SPAN class=120234207-16092003>I
am not convinced about your suggestion for changing Annex D. This is
an interoperability issue between new implementations and old ones.
Changing the standard in this way isn't going to stop existing endpoints
accepting the channels [ unless you have some very interesting paranormal
capabilities in your gateway - in which case why do you need H.323 at
all! Or have you have achieved the ultimate goal - a computer
that does what you want it to do, not what you tell it to do ;-)
]</SPAN></FONT></DIV>
<DIV><FONT face=Arial color=#0000ff size=2><SPAN
class=120234207-16092003></SPAN></FONT> </DIV>
<DIV><FONT face=Arial color=#0000ff size=2>I still believe that the
syntax2002 suggestion by itself is the best solution for this problem.
</FONT></DIV>
<DIV><FONT face=Arial><FONT color=#0000ff><FONT size=2><SPAN
class=120234207-16092003>1. </SPAN>It allows the calling endpoint to
identify which version of the ASN.1 it should use for both receive and
transmit. </FONT></FONT></FONT></DIV>
<DIV><SPAN class=120234207-16092003><FONT face=Arial color=#0000ff size=2>2.
It does not require any knowledge of the problem in existing V0/V1 endpoints
(a very important factor)</FONT></SPAN></DIV>
<DIV><FONT size=+0><FONT size=+0><FONT face=Arial><FONT color=#0000ff><FONT
size=2><SPAN class=120234207-16092003>3. </SPAN>It is an isolated change
that resolves the current problem and does not have any consequences for any
other application area. </FONT></FONT></FONT></FONT></FONT></DIV>
<DIV></SPAN><FONT face=Arial color=#0000ff size=2><SPAN
class=120234207-16092003>4. Trying to engineer a solution that can
anticipate the unforeseeable future will continue to make your head
hurt ;-)</SPAN></FONT></DIV>
<DIV><FONT face=Arial color=#0000ff size=2><SPAN
class=120234207-16092003></SPAN></FONT> </DIV>
<DIV><FONT face=Arial color=#0000ff size=2><SPAN
class=120234207-16092003>Incidentally, since syntax2002 would be an
extended option in T38FaxProfile it would be covered by Fast Connect
changes that allowed such options to be
dropped.</SPAN></FONT></DIV></SPAN></FONT></DIV>
<DIV><FONT face=Arial color=#0000ff size=2><SPAN
class=120234207-16092003></SPAN></FONT> </DIV>
<DIV><FONT face=Arial color=#0000ff size=2><SPAN
class=120234207-16092003>BTW I agree that not using Fast Connect at all is
the best solution. H.245 tunneling or even an H.245 address in the
Setup message typically allows the media to be established before any useful
data can be transmitted - even a purely electronic IVR system is going to
delay before transmitting a message to us poor slow humans. In fact, media
can be established more quickly because it does not require any call
progress messages - not many endpoints accept Fast Connect in Facility
messages.</SPAN></FONT></DIV>
<DIV><FONT face=Arial color=#0000ff size=2><SPAN
class=120234207-16092003></SPAN></FONT> </DIV>
<DIV><FONT face=Arial color=#0000ff size=2><SPAN
class=120234207-16092003>Pete</SPAN></FONT></DIV>
<BLOCKQUOTE dir=ltr
style="PADDING-LEFT: 5px; MARGIN-LEFT: 5px; BORDER-LEFT: #0000ff 2px solid; MARGIN-RIGHT: 0px">
<DIV class=OutlookMessageHeader dir=ltr align=left><FONT face=Tahoma
size=2>-----Original Message-----<BR><B>From:</B> Paul E. Jones
[mailto:paulej@packetizer.com]<BR><B>Sent:</B> 12 September 2003
21:53<BR><B>To:</B> Peter Price; itu-sg16@external.cisco.com;
tsg16q14@itu.int<BR><B>Subject:</B> Re: H.323 Fast Connect and
Versioning<BR><BR></FONT></DIV>
<DIV><FONT face=Arial>Peter,</FONT></DIV>
<DIV><FONT face=Arial></FONT> </DIV>
<DIV><FONT face=Arial>The danger with adding the codepoint for
"syntax2002" is that it does not necessarily encompass all of the rules
for version 2, 3, etc. Since those future versions do not exist, it
presents us with certain problems.</FONT></DIV>
<DIV><FONT face=Arial></FONT> </DIV>
<DIV><FONT face=Arial>Perhaps the right solution is two-fold:</FONT></DIV>
<OL>
<LI><FONT face=Arial>Add a new "syntax2002" field</FONT>
<LI><FONT face=Arial>Allow the called endpoint to modify the
version number field in the Fast Connect proposal. It could *not*
change it if the calling device is version 0 or not using the new
"syntax2002" field, but we could add a rule that says that if the
calling device included "syntax2002", it also means that the called
device may change the version number in the reply to indicate the actual
supported version.</FONT></LI></OL>
<DIV><FONT face=Arial>If we do (2), then we need to change the language in
H.323 to say that parameters shall not be changed, unless explicitly
allowed by the particular "controlling media profile document". For
T.38, that would be Annex D/H.323. For V.150.1, that would be Annex
P/H.323.</FONT></DIV>
<DIV><FONT face=Arial></FONT> </DIV>
<DIV><FONT face=Arial>The video codec issue is an interesting one...
several options can be proposed with various capabilities, but they can't
be changed.</FONT></DIV>
<DIV><FONT face=Arial></FONT> </DIV>
<DIV><FONT face=Arial>There is an implementation approach that could be
used to solve these kinds of issues, but some folks don't like it.
That is: don't use Fast Connect at all-- just do termcap exchange and only
open media channels and ring the remote phone once caps are exchanged and
media is opened. Regardless of whether H.245 is tunneled or on a
separate connection, the exchange of all required messages can be done in
about 3 TCP packets per side.</FONT></DIV>
<DIV><FONT face=Arial></FONT> </DIV>
<DIV><FONT face=Arial>As for the requirement that H.245 tunneling be used
with Fast Connect--- yes, the requirement is there, but folks ignore that
like they do other requirements in the standard ;-) The wording
might be "must support tunneling", which does not mean it has to be
used.</FONT></DIV>
<DIV><FONT face=Arial></FONT> </DIV>
<DIV><FONT face=Arial>Fast Connect certainly has certain advantages over
H.245, but <EM>if</EM> we had never introduced Fast Connect in the first
place, I suspect nobody would think something is missing. Most
likely, folks would have engineered their products to send TCS right away,
would not have alerted the user until media was established, etc.
They would have optimized their code to send TCS,MSDet,OLC in the first
outgoing message, replied with TCS,TCSAck,MSDet,OLCAck,OLC in the reply
TCP packet, and then TCSAck,OLCAck in the sender's second TCP
packet. In the rare case where the proposed OLC is not acceptable,
it would require an extra exchange of messages, but certainly no worse
than Fast Connect today.</FONT></DIV>
<DIV><FONT face=Arial></FONT> </DIV>
<DIV><FONT face=Arial>I'm actually working on a new extension to H.323 to
allowing the calling endpoint to explicitly request that the call
establishment be delayed until a certain point (e.g., bi-directional media
channels are opened). The calling side can control when it lets the
call proceed. Likewise, the called side can control it by not
acknowledging that the requested "delay point" has been reached.
This might be the better way to handle T.38.... except that, as you point
out, there are Fast Connect-only T.38 devices.</FONT></DIV>
<DIV><FONT face=Arial></FONT> </DIV>
<DIV><FONT face=Arial>My head hurts...</FONT></DIV>
<DIV><FONT face=Arial></FONT> </DIV>
<DIV><FONT face=Arial>I really hate to break the rules about changing the
attributes of a Fast Connect proposal.</FONT></DIV>
<DIV><FONT face=Arial></FONT> </DIV>
<DIV><FONT face=Arial>Here's another thought: What if we add text to
Annex D/H.323 that says that if the proposed version is not supported,
then it shall not accept the proposal. If it wants to offer a
"counter proposal", it has two means: H.245 signaling or H.460.6 (Extended
Fast Connect).</FONT></DIV>
<DIV><FONT face=Arial></FONT> </DIV>
<DIV><FONT face=Arial>Paul</FONT></DIV>
<DIV><FONT face=Arial></FONT> </DIV>
<BLOCKQUOTE dir=ltr
style="PADDING-RIGHT: 0px; PADDING-LEFT: 5px; MARGIN-LEFT: 5px; BORDER-LEFT: #000000 2px solid; MARGIN-RIGHT: 0px">
<DIV style="FONT: 10pt arial">----- Original Message ----- </DIV>
<DIV
style="BACKGROUND: #e4e4e4; FONT: 10pt arial; font-color: black"><B>From:</B>
<A title=PeterP@vegastream.com href="mailto:PeterP@vegastream.com">Peter
Price</A> </DIV>
<DIV style="FONT: 10pt arial"><B>To:</B> <A title=paulej@packetizer.com
href="mailto:paulej@packetizer.com">'Paul E. Jones'</A> ; <A
title=itu-sg16@external.cisco.com
href="mailto:itu-sg16@external.cisco.com">itu-sg16@external.cisco.com</A>
; <A title=tsg16q14@itu.int
href="mailto:tsg16q14@itu.int">tsg16q14@itu.int</A> </DIV>
<DIV style="FONT: 10pt arial"><B>Sent:</B> Thursday, September 11, 2003
3:53 AM</DIV>
<DIV style="FONT: 10pt arial"><B>Subject:</B> RE: H.323 Fast Connect and
Versioning</DIV>
<DIV><FONT face=Arial></FONT><FONT face=Arial></FONT><BR></DIV>
<DIV><FONT face=Arial color=#0000ff size=2><SPAN
class=460514806-11092003>Paul,</SPAN></FONT></DIV>
<DIV><FONT face=Arial color=#0000ff size=2><SPAN
class=460514806-11092003></SPAN></FONT> </DIV>
<DIV><FONT face=Arial color=#0000ff size=2><SPAN
class=460514806-11092003>as I said before any solution is likely to be a
bit dirty because of the nature of the problem. I think your
"syntax2002" suggestion is perfectly valid - it is a smaller more
localised change and, especially given the reluctance to add new code
points, is probably a better alternative than t39faxV2. It only
requires a single change to T38FaxProfile rather than changes to both
DataApplicationCapability and DataApplicationMode. There is no
danger that the change could affect anything other than T.38 aware
endpoints.</SPAN></FONT></DIV>
<DIV><FONT face=Arial color=#0000ff size=2><SPAN
class=460514806-11092003></SPAN></FONT> </DIV>
<DIV><FONT face=Arial color=#0000ff size=2><SPAN
class=460514806-11092003>On the subject of H245 tunneling, the problem
scenario we're discussing is Fast Connect and I thought that H.323 V4
says that endpoints using Fast Connect shall use H.245 tunneling!
It doesn't do much for pure T.38 endpoints which don't do any H.245
though.</SPAN></FONT></DIV>
<DIV><FONT face=Arial color=#0000ff size=2><SPAN
class=460514806-11092003></SPAN></FONT> </DIV><FONT size=+0><SPAN
class=460514806-11092003>
<DIV><FONT face=Arial color=#0000ff size=2><SPAN
class=460514806-11092003>The thread has suggested two approaches
</SPAN></FONT></DIV>
<DIV><FONT face=Arial color=#0000ff size=2><SPAN
class=460514806-11092003>1. resolve the issue within the Fast
Connect proposal (or any subsequent requestMode/OLC
etc)</SPAN></FONT></DIV>
<DIV><FONT face=Arial color=#0000ff size=2><SPAN
class=460514806-11092003>2. resolve the issue by modifying some other
part of the standard by introducing "special cases"</SPAN></FONT></DIV>
<DIV><FONT face=Arial color=#0000ff size=2><SPAN
class=460514806-11092003></SPAN></FONT> </DIV>
<DIV><FONT face=Arial><FONT color=#0000ff><FONT size=2><SPAN
class=460514806-11092003>As an implementor, </SPAN>I would prefer to see
a solution within the Fast Connect proposal rather than force other
changes in the standard - the danger of going that route is you don't
know what the downstream consequences are going to be. Containing
the solution in <SPAN class=460514806-11092003>T38FaxProfile
</SPAN>keeps implementation simpler - you receive a message and you know
exactly what you are doing without having to go looking for other
information. Logically, the tunneled H245 messages arrive after
the Setup message and its easier to process the Setup completely before
starting to look at the H.245.</FONT></FONT></FONT></SPAN></FONT></DIV>
<DIV><FONT face=Arial color=#0000ff size=2><SPAN
class=460514806-11092003></SPAN></FONT> </DIV>
<DIV><FONT face=Arial color=#0000ff size=2><SPAN
class=460514806-11092003>Furthermore, if H.323 endpoints are to remain
interoperable with pure T.38 endpoints (are there any?) then the
solution *must* be contained within the Fast Connect
proposal.</SPAN></FONT></DIV>
<DIV><FONT face=Arial color=#0000ff size=2><SPAN
class=460514806-11092003></SPAN></FONT> </DIV>
<DIV><FONT face=Arial color=#0000ff size=2><SPAN
class=460514806-11092003>You suggest that "syntax002" is a bit of a
kludge. It probably is but it does have the advantage of being
isolated. I think that "special cases" in the standard that may
have unforeseen consequences for endpoints that are not interested
in T.38 are very much worse.</SPAN></FONT></DIV>
<DIV><FONT face=Arial color=#0000ff size=2><SPAN
class=460514806-11092003></SPAN></FONT> </DIV>
<DIV><FONT face=Arial color=#0000ff size=2><SPAN
class=460514806-11092003>------------</SPAN></FONT></DIV>
<DIV><FONT face=Arial color=#0000ff size=2><SPAN
class=460514806-11092003></SPAN></FONT> </DIV>
<DIV><FONT face=Arial color=#0000ff size=2><SPAN
class=460514806-11092003>A slight aside here (but
related).</SPAN></FONT></DIV>
<DIV><FONT face=Arial color=#0000ff size=2><SPAN
class=460514806-11092003></SPAN></FONT> </DIV>
<DIV><FONT face=Arial color=#0000ff size=2><SPAN
class=460514806-11092003>Your remark about the way that all endpoints
appear to decode and re-encode the Fast Connect proposals implies that
the rule for not changing the proposals is effectively impossible to
maintain.</SPAN></FONT></DIV>
<DIV><FONT face=Arial color=#0000ff size=2><SPAN
class=460514806-11092003></SPAN></FONT> </DIV>
<DIV><FONT face=Arial color=#0000ff size=2><SPAN
class=460514806-11092003>I only work with audio endpoints that use the
basic audio codecs and T.38 so until this discussion started hadn't
really thought about this issue. It's easy to say you musn't
change, say, the frame count of G729 but for codecs that are
defined as extensible like T.38 (and all the video codecs) there will
always be a problem when new endpoints offer new features to old
endpoints.</SPAN></FONT></DIV>
<DIV><FONT face=Arial color=#0000ff size=2><SPAN
class=460514806-11092003></SPAN></FONT> </DIV>
<DIV><FONT face=Arial color=#0000ff size=2><SPAN
class=460514806-11092003>Perhaps the Fast Connect rule needs some review
to address the specific issue of extensible
capabilities.</SPAN></FONT></DIV>
<DIV><FONT face=Arial color=#0000ff size=2><SPAN
class=460514806-11092003>Have video endpoints already encountered this
problem? </SPAN></FONT></DIV>
<DIV><FONT face=Arial color=#0000ff size=2><SPAN
class=460514806-11092003>D</SPAN></FONT><FONT face=Arial color=#0000ff
size=2><SPAN class=460514806-11092003>o any video endpoint implementors
have any relevent comments here?</SPAN></FONT></DIV>
<DIV><FONT face=Arial color=#0000ff size=2><SPAN
class=460514806-11092003></SPAN></FONT> </DIV>
<DIV><FONT face=Arial color=#0000ff size=2><SPAN
class=460514806-11092003>Peter</SPAN></FONT></DIV>
<BLOCKQUOTE dir=ltr
style="PADDING-LEFT: 5px; MARGIN-LEFT: 5px; BORDER-LEFT: #0000ff 2px solid; MARGIN-RIGHT: 0px">
<DIV class=OutlookMessageHeader dir=ltr align=left><FONT face=Tahoma
size=2>-----Original Message-----<BR><B>From:</B> Paul E. Jones
[mailto:paulej@packetizer.com]<BR><B>Sent:</B> 10 September 2003
23:35<BR><B>To:</B> Peter Price; itu-sg16@external.cisco.com;
tsg16q14@itu.int<BR><B>Subject:</B> Re: H.323 Fast Connect and
Versioning<BR><BR></FONT></DIV>
<DIV><FONT face=Arial>Peter,</FONT></DIV>
<DIV><FONT face=Arial></FONT> </DIV>
<DIV><FONT face=Arial>I've only seen this problem with fax.
To answer your last question, I've only seen T.38 use this kind of
version tag. However, V.150.1 also has versioning information as
part of the object identifier that identifies the capability.
This will be interesting to see if we introduce the same kind of
problem there. In general, it's just not good to advertise the
version through an OLC... it's better to perform a full caps
exchange. The trouble is that modem and (to some extent) fax
timings are such that we must open channels ASAP... before a caps
exchange. (Actually, we could transmit the termcap set in the
Setup message, but few devices support that.)</FONT></DIV>
<DIV><FONT face=Arial></FONT> </DIV>
<DIV><FONT face=Arial>We have had non-compatible payload
specifications before and we resolved that by adding new code
points. However, we've been trying to avoid that. Even so,
we could do it again... it's just less desirable.</FONT></DIV>
<DIV><FONT face=Arial></FONT> </DIV>
<DIV><FONT face=Arial>I had another idea. What we could do is,
within the t38faxProtocol SEQUENCE, we could indicate which syntax is
to be used. Older devices would not see this field and would not
decode it. So, when the reply is re-encoded, it would not be
present. So, even if the version was set to "2", the
"Syntax2002" field, say, would not be present. This would mean
that the 1998 syntax has to be used. A newer endpoint would see
the field and would properly re-encode it in the reply. This is
a bit of a kludge and works only because of the way the ASN.1
encoding/decoding works with every device I've seen.</FONT></DIV>
<DIV><FONT face=Arial></FONT> </DIV>
<DIV><FONT face=Arial>Another solution to the problem might be to
require that endpoint use H.245 tunneling and to advertise their
capabilities in the Setup message. That could allow us to avoid
this problem entirely. I'm just not sure how excited people
would be to be forced to use H.245 tunneling every time they use fax,
modem, or text relay.</FONT></DIV>
<DIV><FONT face=Arial></FONT> </DIV>
<DIV><FONT face=Arial>Paul</FONT></DIV>
<DIV><FONT face=Arial></FONT> </DIV>
<BLOCKQUOTE dir=ltr
style="PADDING-RIGHT: 0px; PADDING-LEFT: 5px; MARGIN-LEFT: 5px; BORDER-LEFT: #000000 2px solid; MARGIN-RIGHT: 0px">
<DIV style="FONT: 10pt arial">----- Original Message ----- </DIV>
<DIV
style="BACKGROUND: #e4e4e4; FONT: 10pt arial; font-color: black"><B>From:</B>
<A title=PeterP@vegastream.com
href="mailto:PeterP@vegastream.com">Peter Price</A> </DIV>
<DIV style="FONT: 10pt arial"><B>To:</B> <A
title=paulej@packetizer.com
href="mailto:paulej@packetizer.com">'Paul E. Jones'</A> ; <A
title=itu-sg16@external.cisco.com
href="mailto:itu-sg16@external.cisco.com">itu-sg16@external.cisco.com</A>
; <A title=tsg16q14@itu.int
href="mailto:tsg16q14@itu.int">tsg16q14@itu.int</A> </DIV>
<DIV style="FONT: 10pt arial"><B>Sent:</B> Wednesday, September 10,
2003 12:34 PM</DIV>
<DIV style="FONT: 10pt arial"><B>Subject:</B> RE: H.323 Fast Connect
and Versioning</DIV>
<DIV><FONT face=Arial color=#0000ff size=2></FONT><BR></DIV>
<DIV><FONT face=Arial>
<DIV><SPAN class=120571215-10092003><FONT color=#0000ff
size=2>Paul,</FONT></SPAN></DIV>
<DIV><SPAN class=120571215-10092003><FONT color=#0000ff
size=2></FONT></SPAN> </DIV>
<DIV><SPAN class=120571215-10092003><FONT color=#0000ff size=2>I
wrote the first part of this email and then reread yours - I was
bogged down in the fax issue but I think you are actually raising a
wider issue aren't you? See part 2 below.</FONT></SPAN></DIV>
<DIV><SPAN class=120571215-10092003><FONT color=#0000ff
size=2></FONT></SPAN> </DIV>
<DIV><SPAN class=120571215-10092003><FONT color=#0000ff
size=2>-------------------------- Part 1 </FONT></SPAN></DIV>
<DIV><SPAN class=120571215-10092003><FONT color=#0000ff size=2>I
don't believe that 5 versions of T38 would result in 5 offered
channels.</FONT></SPAN></DIV>
<DIV><SPAN class=120571215-10092003><FONT color=#0000ff
size=2></FONT></SPAN> </DIV>
<DIV><SPAN class=120571215-10092003><FONT face=Arial>
<DIV><FONT color=#0000ff><FONT size=2><SPAN
class=120571215-10092003>The need for the different capability is
due to the fact that what you are offering is a payload that is
encoded in a different and incompatible way. </SPAN><SPAN
class=120571215-10092003>ie its a bit like offering G.729 and the
sending packets encoded according to G.723.1, they both
represent speech but they are not going to be played out
properly.<SPAN class=390145815-10092003> The single extra bit
introduced into the T.38 payload packet by the 2002 ASN.1 is
backwards incompatible.</SPAN></SPAN></FONT></FONT></DIV>
<DIV><FONT color=#0000ff><FONT size=2><SPAN
class=120571215-10092003></SPAN><FONT face=Tahoma><SPAN
class=120571215-10092003><FONT
face=Arial></FONT></SPAN></FONT></FONT></FONT> </DIV><FONT
color=#0000ff size=2>The problem only exists for endpoints that only
know about the 1998 ASN.1 <SPAN class=390145815-10092003>and
</SPAN>are unaware of the <SPAN
class=390145815-10092003>incompatibility </SPAN>- it is important
that they do not think they can accept the offered
channel.</FONT></FONT></SPAN></DIV>
<DIV><SPAN class=120571215-10092003><FONT color=#0000ff
size=2></FONT></SPAN> </DIV>
<DIV><FONT color=#0000ff><FONT size=2><SPAN
class=120571215-10092003>Once an endpoint is aware of the problem
(ie it knows about the 2002 ASN.1) then it can handle versions >=
V2 (as well as V0 and V1). </SPAN><SPAN
class=120571215-10092003>Of course, this does assume that a
similar <SPAN class=390145815-10092003>incompatibilty
</SPAN>does not creep into the payload ASN.1 in future versions -
but that's down to careful work in the standard development and
editing stage.</SPAN></FONT></FONT></DIV>
<DIV><SPAN class=120571215-10092003><FONT color=#0000ff
size=2></FONT></SPAN> </DIV>
<DIV><FONT color=#0000ff><FONT size=2><SPAN
class=120571215-10092003>I still think adding t38faxV2 (say) to
DataApplicationCapability and DataApplicationMode is the simplest
solution<SPAN class=390145815-10092003>
<DIV><FONT face=Tahoma><FONT face=Arial color=#0000ff size=2><SPAN
class=120571215-10092003><SPAN class=120571215-10092003>[ t38faxV2
would use the same definitions for t38FaxProtocol and t38FaxProfile
- its only the payload that has changed
]. </SPAN></SPAN></FONT></FONT></SPAN></SPAN><FONT
face=Tahoma><FONT face=Arial><SPAN class=120571215-10092003>This
protects the existing T.38 implementations and avoids the need to
break the rule about modifying Fast
Connect proposals.</SPAN></FONT></FONT></FONT></FONT></DIV></DIV>
<DIV><FONT face=Tahoma><FONT face=Arial color=#0000ff size=2><SPAN
class=120571215-10092003><SPAN
class=120571215-10092003></SPAN></SPAN></FONT></FONT> </DIV>
<DIV><FONT color=#0000ff><FONT size=2><SPAN
class=120571215-10092003>The change in the T.38 payload ASN.1 breaks
the fundamental backwards compatibility that ASN.1 is supposed
to <SPAN class=390145815-10092003>guarantee</SPAN> and thus
w</SPAN><FONT face=Tahoma><FONT face=Arial><SPAN
class=120571215-10092003>hatever the final solution there has to be
an element of a hack involved - I think that this change would
isolate the change and protect the rest of the
standard.</SPAN></FONT></FONT></FONT></FONT></DIV>
<DIV><FONT face=Tahoma><FONT face=Arial color=#0000ff size=2><SPAN
class=120571215-10092003></SPAN></FONT></FONT> </DIV>
<DIV><FONT face=Tahoma><SPAN class=120571215-10092003>
<DIV><SPAN class=120571215-10092003><FONT face=Arial color=#0000ff
size=2>-------------------------- Part 2</FONT></SPAN></DIV>
<DIV><SPAN class=120571215-10092003><FONT face=Arial color=#0000ff
size=2></FONT></SPAN> </DIV>
<DIV><SPAN class=120571215-10092003><FONT face=Arial color=#0000ff
size=2>The versioning issue applies to any form of payload,
voice/video/fax/whatever.</FONT></SPAN></DIV>
<DIV><SPAN class=120571215-10092003><FONT face=Arial color=#0000ff
size=2></FONT></SPAN> </DIV>
<DIV><SPAN class=120571215-10092003><FONT face=Arial color=#0000ff
size=2>The problem is still going to exist in early versions of
endpoints that don't understand the consequence of accepting
versions that they do not understand fully. If a new version
of a codec<SPAN class=390145815-10092003>'s payload</SPAN> is
not backwards compatible then I would assert that it is a new codec
and must be signalled as a different capability.</FONT></SPAN></DIV>
<DIV><SPAN class=120571215-10092003><FONT face=Arial color=#0000ff
size=2></FONT></SPAN> </DIV>
<DIV><SPAN class=120571215-10092003><SPAN
class=390145815-10092003><FONT face=Arial color=#0000ff size=2>The
issue of multiple variations already exists anyway although not (to
my knowledge) with version numbers.</FONT></SPAN></SPAN></DIV>
<DIV><SPAN class=120571215-10092003><SPAN
class=390145815-10092003><FONT face=Arial color=#0000ff
size=2>Endpoints already offer multiple packet sizes for exactly the
reason that you are not supposed to alter the Fast Connect
proposal. What happens when somebody starts to offer
g729Extensions and has to offer all the combinations of Annexes
because they don't know what the other end can use ( I make that 64
proposals in each direction without adding further annexes!
)?</FONT></SPAN></SPAN></DIV>
<DIV><SPAN class=120571215-10092003><SPAN
class=390145815-10092003><FONT face=Arial color=#0000ff
size=2></FONT></SPAN></SPAN> </DIV>
<DIV><SPAN class=120571215-10092003><SPAN class=390145815-10092003>
<DIV><SPAN class=120571215-10092003><FONT face=Arial><FONT
color=#0000ff><FONT size=2>I don't see that relaxing the rule about
modifying the version in a Fast Connect channel will help<SPAN
class=390145815-10092003> resolve the problem of having to offer
multiple proposals. You either have to allow *anything* to be
modified or stick to the current rule. Exceptions allowing
certain fields to be modified just makes life much more
difficult and confusing.</SPAN></FONT></FONT></FONT></SPAN></DIV>
<DIV><SPAN class=120571215-10092003><FONT face=Arial color=#0000ff
size=2></FONT></SPAN> </DIV></SPAN></SPAN></DIV></SPAN></FONT></DIV>
<DIV><FONT face=Tahoma><FONT face=Arial><SPAN
class=120571215-10092003></SPAN></FONT></FONT><FONT
face=Tahoma><SPAN class=120571215-10092003>
<DIV><FONT face=Arial><FONT color=#0000ff><FONT size=2><SPAN
class=120571215-10092003>T.38 is the only <SPAN
class=390145815-10092003>codec </SPAN>I am aware of that
actually <SPAN class=390145815-10092003>uses</SPAN> a version
number<SPAN class=390145815-10092003> in this manner</SPAN>.
Are there any others?<SPAN class=390145815-10092003>
</SPAN></SPAN><SPAN class=120571215-10092003>Why was it introduced
in T.38?<SPAN class=390145815-10092003> Perhaps this is a
lesson for the future about the value of introducing of such a field
in other codecs.</SPAN></SPAN></FONT></FONT></FONT></DIV>
<DIV><SPAN class=120571215-10092003><FONT face=Arial color=#0000ff
size=2></FONT></SPAN> </DIV>
<DIV><FONT face=Arial color=#0000ff
size=2>Peter</FONT></SPAN></FONT></DIV></DIV></FONT></DIV>
<BLOCKQUOTE dir=ltr
style="PADDING-LEFT: 5px; MARGIN-LEFT: 5px; BORDER-LEFT: #0000ff 2px solid; MARGIN-RIGHT: 0px">
<DIV class=OutlookMessageHeader dir=ltr align=left><FONT
face=Tahoma size=2>-----Original Message-----<BR><B>From:</B> Paul
E. Jones [mailto:paulej@packetizer.com]<BR><B>Sent:</B> 10
September 2003 16:01<BR><B>To:</B> Peter Price;
itu-sg16@external.cisco.com; tsg16q14@itu.int<BR><B>Subject:</B>
Re: H.323 Fast Connect and Versioning<BR><BR></FONT></DIV>
<DIV><FONT face=Arial>Peter,</FONT></DIV>
<DIV><FONT face=Arial></FONT> </DIV>
<DIV><FONT face=Arial>I think you're on the right track. We
could avoid ASN.1 changes by introducing the new capability as a
generic data capability, but a new capability is required here, I
think.</FONT></DIV>
<DIV><FONT face=Arial></FONT> </DIV>
<DIV><FONT face=Arial>The problem, as I see it, is that when we
use Fast Connect, we can't alert the calling side as to what
version the called side actually supports. This suggests
that if we have 5 versions of T.38, the calling side would have to
propose a channel for each version independently. That's
horrible. It's only complicated further by the fact that
T.38 may not be signaled by itself-- it might be part of audio
proposals that also include modem, text over IP, VBD, or other
media. It might even be that there are several versions of
the modem (V.150.1) protocol advertised.</FONT></DIV>
<DIV><FONT face=Arial></FONT> </DIV>
<DIV><FONT face=Arial>I think the only real solution to this
problem is to allow the Fast Connect proposals to be altered by
the called endpoint such that they can change the version number..
and nothing else. H.323 has an explicit statement that says
that the proposals can't be modified before returning them, but
perhaps this simple exception might resolve these issues. I
think without such, it's going to be terrible
complicated.</FONT></DIV>
<DIV><FONT face=Arial></FONT> </DIV>
<DIV><FONT face=Arial>Paul</FONT></DIV>
<DIV><FONT face=Arial></FONT> </DIV>
<BLOCKQUOTE dir=ltr
style="PADDING-RIGHT: 0px; PADDING-LEFT: 5px; MARGIN-LEFT: 5px; BORDER-LEFT: #000000 2px solid; MARGIN-RIGHT: 0px">
<DIV style="FONT: 10pt arial">----- Original Message -----
</DIV>
<DIV
style="BACKGROUND: #e4e4e4; FONT: 10pt arial; font-color: black"><B>From:</B>
<A title=PeterP@vegastream.com
href="mailto:PeterP@vegastream.com">Peter Price</A> </DIV>
<DIV style="FONT: 10pt arial"><B>To:</B> <A
title=paulej@PACKETIZER.COM
href="mailto:'paulej@PACKETIZER.COM'">'paulej@PACKETIZER.COM'</A>
; <A title=itu-sg16@external.cisco.com
href="mailto:itu-sg16@external.cisco.com">itu-sg16@external.cisco.com</A>
</DIV>
<DIV style="FONT: 10pt arial"><B>Sent:</B> Wednesday, September
10, 2003 3:23 AM</DIV>
<DIV style="FONT: 10pt arial"><B>Subject:</B> RE: H.323 Fast
Connect and Versioning</DIV>
<DIV><BR></DIV>
<DIV>
<DIV><SPAN class=370241707-10092003><FONT face=Arial
color=#0000ff size=2>Paul wrote</FONT></SPAN></DIV>
<DIV><SPAN class=370241707-10092003><FONT face=Arial
color=#0000ff size=2></FONT></SPAN> </DIV>
<DIV><FONT face=Arial><FONT color=#0000ff><FONT size=2><SPAN
class=370241707-10092003>"</SPAN>Perhaps we can require the
calling device to not transmit any data until it receives at
least one IFP packet from the called side and determines the
ASN.1 version used to encode the message.<SPAN
class=370241707-10092003>"</SPAN></FONT></FONT></FONT></DIV>
<DIV><FONT face=Arial><FONT color=#0000ff><FONT size=2><SPAN
class=370241707-10092003></SPAN></FONT></FONT></FONT> </DIV>
<DIV><FONT face=Arial><FONT color=#0000ff><FONT size=2><SPAN
class=370241707-10092003>Unfortunately this won't work -
although typically the called endpoint will provide the first
IFP (Probably a CED) this doesn't work when you poll for a fax -
in that case the calling endpoint will probably want to send the
first IFP.</SPAN></FONT></FONT></FONT></DIV>
<DIV><FONT face=Arial><FONT color=#0000ff><FONT size=2><SPAN
class=370241707-10092003></SPAN></FONT></FONT></FONT> </DIV>
<DIV><FONT face=Arial><FONT color=#0000ff><FONT size=2><SPAN
class=370241707-10092003>The only way I can see out of this is
to add a new data application (say, t38faxV2) to
DataApplicationCapability etc in the H.245
ASN.1. t38fax would use the 1998 ASN.1 and
t38faxV2 would use the 2002 ASN.1 - and future carefully checked
modifications ;-). Now there's no problem, a 2002 aware
endpoint can offer both versions and a 1998 aware endpoint can
only accept the ASN.1 it
understands.</SPAN></FONT></FONT></FONT></DIV>
<DIV><FONT face=Arial><FONT color=#0000ff><FONT size=2><SPAN
class=370241707-10092003></SPAN></FONT></FONT></FONT> </DIV>
<DIV><FONT face=Arial><FONT color=#0000ff><FONT size=2><SPAN
class=370241707-10092003></SPAN></FONT></FONT></FONT> </DIV>
<DIV><FONT face=Arial><FONT color=#0000ff><FONT size=2><SPAN
class=370241707-10092003>Pete
Price</SPAN></FONT></FONT></FONT></DIV>
<DIV><FONT face=Arial><FONT color=#0000ff><FONT size=2><SPAN
class=370241707-10092003>Vegastream
Limited</SPAN></FONT></FONT></FONT></DIV>
<DIV><FONT face=Arial color=#0000ff
size=2></FONT> </DIV></DIV>
<BLOCKQUOTE dir=ltr
style="PADDING-LEFT: 5px; MARGIN-LEFT: 5px; BORDER-LEFT: #0000ff 2px solid; MARGIN-RIGHT: 0px">
<DIV class=OutlookMessageHeader dir=ltr align=left><FONT
face=Tahoma size=2>-----Original Message-----<BR><B>From:</B>
paulej@PACKETIZER.COM
[mailto:paulej@PACKETIZER.COM]<BR><B>Sent:</B> 09 September
2003 20:32<BR><B>To:</B>
itu-sg16@external.cisco.com<BR><B>Subject:</B> H.323 Fast
Connect and Versioning<BR><BR></FONT></DIV>
<DIV><FONT face=Arial>Folks,</FONT></DIV>
<DIV><FONT face=Arial></FONT> </DIV>
<DIV><FONT face=Arial>Today, I was exchanging e-mail with
somebody over the fax version number issue and the different
syntax that is used (1998 vs 2002).</FONT></DIV>
<DIV><FONT face=Arial></FONT> </DIV>
<DIV><FONT face=Arial>If we open H.245 and exchange a full set
of capabilities, and H.323 endpoint could determine the
version supported by the other side and open a channel
supporting that particular version. However, I don't
think any text is explicitly clear on that.</FONT></DIV>
<DIV><FONT face=Arial></FONT> </DIV>
<DIV><FONT face=Arial>Another scenario-- and one I have
more trouble with-- is Fast Connect. If a calling
endpoint populates the fastStart element with "version 2"
proposals, for example, the called side (say, a version 0
device) might accept the proposal and return the
response. However, it is not allowed to modify the
version field. The reason is that Fast Connect proposals
are not ordered in a way such that replies must be ordered the
same way. Rather, the calling device determines which
proposals are accepted based on characteristics of the
proposals returned (e.g., codec type, samples per packet, or
other information). In some cases, a calling endpoint
will actually not try to "match" the proposal returned, but
just accept it as a proposal and run with it.</FONT></DIV>
<DIV><FONT face=Arial></FONT> </DIV>
<DIV><FONT face=Arial>The problem is that if a calling device
proposes version 2 and the called device returns version 2
(but is actually a v0 device), then the wrong syntax will be
transmitted on the wire. Thus, the text needs to state
somewhere one of these options (or something
similar):</FONT></DIV>
<OL>
<LI><FONT face=Arial>The calling device must offer a
proposal for each version it wants to potentially use and
the called device must accept the first proposal it can
accept (in order of the proposals) and the called device
must not accept any proposal for a version it does not
support</FONT>
<LI><FONT face=Arial>The calling device must wait for
capability exchange to complete to determine the actual
supported version of the other device</FONT></LI></OL>
<DIV><FONT face=Arial>Alternatively, we could make an
allowance for the endpoint to change the version number in the
Fast Connect proposal, but I don't think that's a good idea,
as it would quite possibly break interoperability with some
devices.</FONT></DIV>
<DIV><FONT face=Arial></FONT> </DIV>
<DIV><FONT face=Arial>What would a version 0 device do today
if it received a Fast Connect proposal advertising version
2? Would it accept it? I suspect so and I'm
afraid that we might have some interop problems regardless of
the direction we go.</FONT></DIV>
<DIV><FONT face=Arial></FONT> </DIV>
<DIV><FONT face=Arial>Perhaps we can require the calling
device to not transmit any data until it receives at least one
IFP packet from the called side and determines the ASN.1
version used to encode the message. As much as we can
push onto the shoulders of a v2 device, the better, as I don't
think we have any real deployments in the field (yet)... might
be wrong, but I think it would be a far less significant
impact on that side.</FONT></DIV>
<DIV><FONT face=Arial></FONT> </DIV>
<DIV><FONT face=Arial>I'm open to suggestions. Perhaps
this issue is even addressed and I've simply overlooked
it.</FONT></DIV>
<DIV><FONT face=Arial></FONT> </DIV>
<DIV><FONT face=Arial>Thanks,</FONT></DIV>
<DIV><FONT face=Arial>Paul</FONT></DIV>
<DIV><FONT face=Arial></FONT> </DIV>
<DIV><FONT
face=Arial></FONT> </DIV></BLOCKQUOTE></BLOCKQUOTE></BLOCKQUOTE></BLOCKQUOTE></BLOCKQUOTE></BLOCKQUOTE></BLOCKQUOTE></BLOCKQUOTE></BLOCKQUOTE></BODY></HTML>