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<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></BODY></HTML>