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<div class=Section1>
<p class=MsoNormal><span style='color:#1F497D'>Hi Paul,<o:p></o:p></span></p>
<p class=MsoNormal><span style='color:#1F497D'><o:p> </o:p></span></p>
<p class=MsoNormal><span style='color:#1F497D'>I agree that the problem which I
touched has broader scope than the one resulted from the attempt to solve the ETSI
TS 101 804 – 2 issue.<o:p></o:p></span></p>
<p class=MsoNormal><span style='color:#1F497D'>So my preference is to put some
clarification/fixing text into v7, to help resolve the issue and continue the
work if needed into v8.<o:p></o:p></span></p>
<p class=MsoNormal><span style='color:#1F497D'><o:p> </o:p></span></p>
<p class=MsoNormal><span style='color:#1F497D'>I tried to classify the problems
introduced by ETSI TS 101 804 – 2 and state what I believe is the reasonable
H.323 behavior for these cases and where it should be defined.<o:p></o:p></span></p>
<p class=MsoNormal><span style='color:#1F497D'>I found the following two groups:<o:p></o:p></span></p>
<p class=MsoListParagraph style='text-indent:-.25in;mso-list:l0 level1 lfo1'><![if !supportLists]><span
style='mso-list:Ignore'>1)<span style='font:7.0pt "Times New Roman"'>
</span></span><![endif]><span style='color:#1F497D'>Receiving of incorrectly
encoded H.225.0/Q.931 message.<o:p></o:p></span></p>
<p class=MsoNormal style='margin-left:.5in'><span style='color:#1F497D'>Some
facts:<o:p></o:p></span></p>
<p class=MsoListParagraph style='margin-left:1.0in;text-indent:-.25in;
mso-list:l0 level2 lfo1'><![if !supportLists]><span style='color:#1F497D'><span
style='mso-list:Ignore'>a.<span style='font:7.0pt "Times New Roman"'>
</span></span></span><![endif]><span style='color:#1F497D'>H.245 has precisely
one response to any incorrectly encoded message: (FunctionNotSupported.cause.syntaxError)<o:p></o:p></span></p>
<p class=MsoListParagraph style='margin-left:1.0in;text-indent:-.25in;
mso-list:l0 level2 lfo1'><![if !supportLists]><span style='color:#1F497D'><span
style='mso-list:Ignore'>b.<span style='font:7.0pt "Times New Roman"'>
</span></span></span><![endif]><span style='color:#1F497D'>RAS has precisely
one response to any incorrectly encoded message: (messageNotUnderstood a.k.a
XRS)<o:p></o:p></span></p>
<p class=MsoListParagraph style='margin-left:1.0in;text-indent:-.25in;
mso-list:l0 level2 lfo1'><![if !supportLists]><span style='color:#1F497D'><span
style='mso-list:Ignore'>c.<span style='font:7.0pt "Times New Roman"'>
</span></span></span><![endif]><span style='color:#1F497D'>Q.931 has very
detailed approach to what to do with incorrectly encoded messages.<o:p></o:p></span></p>
<p class=MsoListParagraph style='margin-left:1.0in'><span style='color:#1F497D'>So
detailed that for example the processed of: <o:p></o:p></span></p>
<p class=MsoListParagraph style='margin-left:1.0in;text-indent:.5in'><span
style='color:#1F497D'>incorrect protocol discriminator at the top level of the
message differs from the processing of <o:p></o:p></span></p>
<p class=MsoListParagraph style='margin-left:1.0in;text-indent:.5in'><span
style='color:#1F497D'>incorrect protocol discriminator inside user-User IE. <o:p></o:p></span></p>
<p class=MsoListParagraph style='margin-left:1.0in;text-indent:.5in'><span
style='color:#1F497D'><o:p> </o:p></span></p>
<p class=MsoListParagraph style='margin-left:1.0in;text-indent:-.25in;
mso-list:l0 level2 lfo1'><![if !supportLists]><span style='color:#1F497D'><span
style='mso-list:Ignore'>d.<span style='font:7.0pt "Times New Roman"'>
</span></span></span><![endif]><span style='color:#1F497D'>H.225.0 7.1 provides
very limited set of rules for error handling, I found these:<o:p></o:p></span></p>
<p class=MsoListParagraph style='margin-left:1.5in;text-indent:-1.5in;
mso-text-indent-alt:-9.0pt;mso-list:l0 level3 lfo1'><![if !supportLists]><span
style='color:#1F497D'><span style='mso-list:Ignore'><span style='font:7.0pt "Times New Roman"'>
</span>i.<span style='font:7.0pt "Times New Roman"'>
</span></span></span><![endif]><span style='color:#1F497D'>Implementations
shall follow ITU-T Rec. Q.931 as specified in this Recommendation.<o:p></o:p></span></p>
<p class=MsoListParagraph style='margin-left:1.5in;text-indent:-1.5in;
mso-text-indent-alt:-9.0pt;mso-list:l0 level3 lfo1'><![if !supportLists]><span
style='color:#1F497D'><span style='mso-list:Ignore'><span style='font:7.0pt "Times New Roman"'>
</span>ii.<span style='font:7.0pt "Times New Roman"'>
</span></span></span><![endif]><span style='color:#1F497D'>The H.225.0 endpoint
may ignore all optional messages it does not support without harming
interoperability<o:p></o:p></span></p>
<p class=MsoListParagraph style='margin-left:1.5in;text-indent:-1.5in;
mso-text-indent-alt:-9.0pt;mso-list:l0 level3 lfo1'><![if !supportLists]><span
style='color:#1F497D'><span style='mso-list:Ignore'><span style='font:7.0pt "Times New Roman"'>
</span>iii.<span style='font:7.0pt "Times New Roman"'>
</span></span></span><![endif]><span style='color:#1F497D'>The H.225.0 endpoint
… but shall respond to an unknown message with a Status message<o:p></o:p></span></p>
<p class=MsoListParagraph style='margin-left:1.5in;text-indent:-1.5in;
mso-text-indent-alt:-9.0pt;mso-list:l0 level3 lfo1'><![if !supportLists]><span
style='color:#1F497D'><span style='mso-list:Ignore'><span style='font:7.0pt "Times New Roman"'>
</span>iv.<span style='font:7.0pt "Times New Roman"'>
</span></span></span><![endif]><span style='color:#1F497D'>Procedures for
receiving unrecognized "comprehension required" information elements
shall apply according to 5.8.7.1/Q.931.<o:p></o:p></span></p>
<p class=MsoListParagraph style='margin-left:1.5in;text-indent:-1.5in;
mso-text-indent-alt:-9.0pt;mso-list:l0 level3 lfo1'><![if !supportLists]><span
style='color:#1F497D'><span style='mso-list:Ignore'><span style='font:7.0pt "Times New Roman"'>
</span>v.<span style='font:7.0pt "Times New Roman"'>
</span></span></span><![endif]><span style='color:#1F497D'>Endpoints not
supporting Q.931 shifted code sets shall ignore all Q.931 messages using such
methods.<o:p></o:p></span></p>
<p class=MsoListParagraph style='margin-left:1.5in'><span style='color:#1F497D'><o:p> </o:p></span></p>
<p class=MsoListParagraph style='margin-left:1.0in'><b><span style='color:#1F497D'>The
BIG question is: shall Implementations follow ITU-T Rec. Q.931 clause 5.8 “Handling
of error conditions” or not.<o:p></o:p></span></b></p>
<p class=MsoListParagraph style='margin-left:1.0in'><b><span style='color:#1F497D'>Should
we have such an elaborate error handling processing for Q.931 messages, while
the rest works well with simple mechanisms?<o:p></o:p></span></b></p>
<p class=MsoListParagraph style='margin-left:1.0in'><b><span style='color:#1F497D'><o:p> </o:p></span></b></p>
<p class=MsoListParagraph style='text-indent:-.25in;mso-list:l0 level1 lfo1'><![if !supportLists]><span
style='mso-list:Ignore'>2)<span style='font:7.0pt "Times New Roman"'>
</span></span><![endif]><span style='color:#1F497D'>Behavior of an H.323 entity
receiving a STATUS message with callState indicating a call state, which differs
from the one known by the H.323 entity.<o:p></o:p></span></p>
<p class=MsoListParagraph><span style='color:#1F497D'>Q.931 specifies for
example that if STATUS received with callState other than <b>null</b> and the
known call state for this call is null then STATUS should be responded with
RELEASE COMPLETE.<o:p></o:p></span></p>
<p class=MsoListParagraph style='text-indent:-.25in;mso-list:l0 level1 lfo1'><![if !supportLists]><span
style='mso-list:Ignore'>3)<span style='font:7.0pt "Times New Roman"'>
</span></span><![endif]><span style='color:#1F497D'>Behavior of an H.323 entity
when SETUP is not acknowledged during T303 timeout.<o:p></o:p></span></p>
<p class=MsoNormal style='margin-left:.5in'><span style='color:#1F497D'>Q.931
specifies that SETUP needs to be retransmitted.<o:p></o:p></span></p>
<p class=MsoNormal><span style='color:#1F497D'><o:p> </o:p></span></p>
<p class=MsoNormal><span style='color:#1F497D'>======================================================================================<o:p></o:p></span></p>
<p class=MsoNormal><span style='color:#1F497D'><o:p> </o:p></span></p>
<p class=MsoNormal><span style='color:#1F497D'>So my proposal is (I’ll
work on precise wording, this is just the essence):<o:p></o:p></span></p>
<p class=MsoNormal><span style='color:#1F497D'><o:p> </o:p></span></p>
<p class=MsoListParagraph style='text-indent:-.25in;mso-list:l3 level1 lfo4'><![if !supportLists]><span
style='color:#1F497D'><span style='mso-list:Ignore'>1)<span style='font:7.0pt "Times New Roman"'>
</span></span></span><![endif]><span style='color:#1F497D'>Remove from H.225.0
7.1 the sentences indicated by 1) d. ii-v. above.<o:p></o:p></span></p>
<p class=MsoListParagraph style='text-indent:-.25in;mso-list:l3 level1 lfo4'><![if !supportLists]><span
style='color:#1F497D'><span style='mso-list:Ignore'>2)<span style='font:7.0pt "Times New Roman"'>
</span></span></span><![endif]><span style='color:#1F497D'>Add new section
H.225.0 7.1.1 dedicated to H.225.0/Q.931 messages error handling and stating the
following:<o:p></o:p></span></p>
<p class=MsoListParagraph style='margin-left:1.0in;text-indent:-.25in;
mso-list:l3 level2 lfo4'><![if !supportLists]><span style='color:#1F497D'><span
style='mso-list:Ignore'>a.<span style='font:7.0pt "Times New Roman"'>
</span></span></span><![endif]><span style='color:#1F497D'>Q.931 section 5.8
does not apply to H.225.0 endpoints.<o:p></o:p></span></p>
<p class=MsoListParagraph style='margin-left:1.0in;text-indent:-.25in;
mso-list:l3 level2 lfo4'><![if !supportLists]><span style='color:#1F497D'><span
style='mso-list:Ignore'>b.<span style='font:7.0pt "Times New Roman"'>
</span></span></span><![endif]><span style='color:#1F497D'>The H.225.0 endpoint
may ignore all optional messages it does not support without harming
interoperability<o:p></o:p></span></p>
<p class=MsoListParagraph style='margin-left:1.0in;text-indent:-.25in;
mso-list:l3 level2 lfo4'><![if !supportLists]><span style='color:#1F497D'><span
style='mso-list:Ignore'>c.<span style='font:7.0pt "Times New Roman"'>
</span></span></span><![endif]><span style='color:#1F497D'>The H.225.0 endpoint
… but shall respond with a Status message <b>containing cause No. 95 </b>to
any H.225.0 message <b>it cannot understand or decode due to Q.931 or ASN.1 encoding
error.</b><o:p></o:p></span></p>
<p class=MsoListParagraph style='text-indent:-.25in;mso-list:l3 level1 lfo4'><![if !supportLists]><span
style='color:#1F497D'><span style='mso-list:Ignore'>3)<span style='font:7.0pt "Times New Roman"'>
</span></span></span><![endif]><span style='color:#1F497D'>Add to section 8.6 new
paragraph (probably after the current third paragraph) stating that <o:p></o:p></span></p>
<p class=MsoNormal style='margin-left:.5in'><span style='color:#1F497D'>“An
H.323 entity receiving a STATUS message with a callState indicating a call
state other then <b>null</b> and containing a callID value which is does not
correspond to any of the calls currently handled by the entity <b>may</b>
respond to STATUS message with RELEASE COMPLETE containing the CRV and callID
from the STATUS message.”<o:p></o:p></span></p>
<p class=MsoListParagraph style='text-indent:-.25in;mso-list:l3 level1 lfo4'><![if !supportLists]><span
style='color:#1F497D'><span style='mso-list:Ignore'>4)<span style='font:7.0pt "Times New Roman"'>
</span></span></span><![endif]><span style='color:#1F497D'>Add to section 8.6 new
paragraph (probably at the end) stating that <o:p></o:p></span></p>
<p class=MsoListParagraph><span style='color:#1F497D'>“On expiration of
the T303 the H.323 entity shall not retransmit the SETUP message, it shall clear
the call according to the Phase E procedures defined in section 8.5.”<o:p></o:p></span></p>
<p class=MsoNormal style='margin-left:.5in'><span style='color:#1F497D'><o:p> </o:p></span></p>
<p class=MsoListParagraph style='margin-left:1.0in'><span style='color:#1F497D'><o:p> </o:p></span></p>
<p class=MsoNormal><span style='color:#1F497D'>I hope this does not disturb
H.323/H.225.0 too much and we can agree at least on part of it.<o:p></o:p></span></p>
<p class=MsoNormal><span style='color:#1F497D'>I will prepare a contribution
with the proposal outlining the above to the meeting.<o:p></o:p></span></p>
<p class=MsoNormal><span style='color:#1F497D'><o:p> </o:p></span></p>
<p class=MsoNormal><span style='color:#1F497D'>Does this make sense?<o:p></o:p></span></p>
<p class=MsoNormal><span style='color:#1F497D'><o:p> </o:p></span></p>
<p class=MsoNormal><span style='color:#1F497D'>Thanks,<o:p></o:p></span></p>
<p class=MsoNormal><span style='color:#1F497D'>Sasha<o:p></o:p></span></p>
<p class=MsoNormal><span style='color:#1F497D'><o:p> </o:p></span></p>
<p class=MsoNormal><span style='color:#1F497D'><o:p> </o:p></span></p>
<p class=MsoNormal><span style='color:#1F497D'><o:p> </o:p></span></p>
<p class=MsoNormal><span style='color:#1F497D'><o:p> </o:p></span></p>
<div>
<div style='border:none;border-top:solid #B5C4DF 1.0pt;padding:3.0pt 0in 0in 0in'>
<p class=MsoNormal><b><span style='font-size:10.0pt;font-family:"Tahoma","sans-serif"'>From:</span></b><span
style='font-size:10.0pt;font-family:"Tahoma","sans-serif"'> Paul E. Jones
[mailto:paulej@packetizer.com] <br>
<b>Sent:</b> Wednesday, October 07, 2009 10:27 PM<br>
<b>To:</b> Sasha Ruditsky; itu-sg16@lists.packetizer.com<br>
<b>Subject:</b> RE: [itu-sg16] AVD-3813 Handling Of Error Conditions in H.323<o:p></o:p></span></p>
</div>
</div>
<p class=MsoNormal><o:p> </o:p></p>
<p class=MsoNormal><span style='color:#1F497D'>Sasha,<o:p></o:p></span></p>
<p class=MsoNormal><span style='color:#1F497D'><o:p> </o:p></span></p>
<p class=MsoNormal><span style='color:#1F497D'>I cannot disagree with you on
this example. Q.931 only addresses issues in Q.931, but H.225.0 ought to
address issues in the ASN.1. Where there are possible conflicts, we ought
to make a clear statement.<o:p></o:p></span></p>
<p class=MsoNormal><span style='color:#1F497D'><o:p> </o:p></span></p>
<p class=MsoNormal><span style='color:#1F497D'>H.323 only has a very small
section on protocol error handling (8.6) and would be a good place to
expand. It would be a good place to address any general issues that might
arise from H.225.0 and/or H.245.<o:p></o:p></span></p>
<p class=MsoNormal><span style='color:#1F497D'><o:p> </o:p></span></p>
<p class=MsoNormal><span style='color:#1F497D'>H.225.0 would be a good place to
expand on things specific to H.225.0, though not necessarily in section 7.1,
since we do also have to cover non Q.931 error issues.<o:p></o:p></span></p>
<p class=MsoNormal><span style='color:#1F497D'><o:p> </o:p></span></p>
<p class=MsoNormal><span style='color:#1F497D'>In general, though, H.225.0 does
work a lot like Q.931, which is dictated by the opening statement in 7.1 that
reads “Implementations shall follow ITU-T Q.931 as specified in this
Recommendation.” This statement has led to confusion over
implementation of timers, error codes, etc. over the years. While this
statement exists, it’s also important that developers recognize that
H.225.0 is not Q.931. I’ve seen many diagrams that show H.245 and
“H.225.0/Q.931” as components of H.323, which is not accurate.<o:p></o:p></span></p>
<p class=MsoNormal><span style='color:#1F497D'><o:p> </o:p></span></p>
<p class=MsoNormal><span style='color:#1F497D'>If we can reach agreement on
specific text at this upcoming meeting, we could clarify some issues in the v7
document. If not, we can certainly entertain an amendment to v7. Do
you have a list of similar issues and a specific proposal? One thing that
concerns me, obviously, is putting in text of this nature at the last minute
without wide review. As such, I’d really like to discuss specific
proposals on this via the mailing list in advance of the meeting to seek
implementer input. We might even want to take this to the H.323
implementers list: <a href="http://www.packetizer.com/ipmc/h323/lists.html">http://www.packetizer.com/ipmc/h323/lists.html</a><o:p></o:p></span></p>
<p class=MsoNormal><span style='color:#1F497D'><o:p> </o:p></span></p>
<p class=MsoNormal><span style='color:#1F497D'>Paul<o:p></o:p></span></p>
<p class=MsoNormal><span style='color:#1F497D'><o:p> </o:p></span></p>
<div style='border:none;border-left:solid blue 1.5pt;padding:0in 0in 0in 4.0pt'>
<div>
<div style='border:none;border-top:solid #B5C4DF 1.0pt;padding:3.0pt 0in 0in 0in'>
<p class=MsoNormal><b><span style='font-size:10.0pt;font-family:"Tahoma","sans-serif"'>From:</span></b><span
style='font-size:10.0pt;font-family:"Tahoma","sans-serif"'> Sasha Ruditsky
[mailto:sasha@radvision.com] <br>
<b>Sent:</b> Monday, October 05, 2009 2:31 PM<br>
<b>To:</b> Paul E. Jones; itu-sg16@lists.packetizer.com<br>
<b>Subject:</b> RE: [itu-sg16] AVD-3813 Handling Of Error Conditions in H.323<o:p></o:p></span></p>
</div>
</div>
<p class=MsoNormal><o:p> </o:p></p>
<p class=MsoNormal><span style='color:#1F497D'>Hi Paul,<o:p></o:p></span></p>
<p class=MsoNormal><span style='color:#1F497D'><o:p> </o:p></span></p>
<p class=MsoNormal><span style='color:#1F497D'>Yes, I am looking for a Broader
statement. <o:p></o:p></span></p>
<p class=MsoNormal><span style='color:#1F497D'>Specifically, my problem is the
fact that ETSI TS 101 804 – 2 defines procedures referring to Q.931
sections.<o:p></o:p></span></p>
<p class=MsoNormal><span style='color:#1F497D'><o:p> </o:p></span></p>
<p class=MsoNormal><span style='color:#1F497D'>Let consider one example from
ETSI TS 101 804 – 2:<o:p></o:p></span></p>
<p class=MsoNormal><b><span style='font-size:10.0pt;color:#1F497D'>BCC_TE_S_U00_07
clause 5.8.6.1 [4]<o:p></o:p></span></b></p>
<p class=MsoNormal><span style='font-size:10.0pt;color:#1F497D'>Ensure that the
IUT in the Null call state U0, on receipt of a SETUP message with a mandatory
information element<o:p></o:p></span></p>
<p class=MsoNormal><span style='font-size:10.0pt;color:#1F497D'>missing,<o:p></o:p></span></p>
<p class=MsoNormal><span style='font-size:10.0pt;color:#1F497D'>sends a RELEASE
COMPLETE message containing a Cause information element indicating the cause
value 96<o:p></o:p></span></p>
<p class=MsoNormal><span style='font-size:10.0pt;color:#1F497D'>"mandatory
information element missing" and remains in the Null call state U0.<o:p></o:p></span></p>
<p class=MsoNormal><span style='color:#1F497D'><o:p> </o:p></span></p>
<p class=MsoNormal><span style='color:#1F497D'>Which suggest to the reader that
Q.931 section 5.8.6.1 (and some other explicitly referenced sections) <o:p></o:p></span></p>
<p class=MsoNormal><span style='color:#1F497D'>is the way H.323 should be
implemented.<o:p></o:p></span></p>
<p class=MsoNormal><span style='color:#1F497D'><o:p> </o:p></span></p>
<p class=MsoNormal><span style='color:#1F497D'>What I want to achieve is an
explicit statement in H.323 or H.225.0, which would say that this is not the
case,<o:p></o:p></span></p>
<p class=MsoNormal><span style='color:#1F497D'>that these sections do not
apply, instead… and here we do need to provide something which would <o:p></o:p></span></p>
<p class=MsoNormal><span style='color:#1F497D'>close the gap created by this
unspecified Cause code value.<o:p></o:p></span></p>
<p class=MsoNormal><span style='color:#1F497D'><o:p> </o:p></span></p>
<p class=MsoNormal><span style='color:#1F497D'>The problem to select such cause
is stemmed from the fact that syntax of Q.931 messages and syntax of <o:p></o:p></span></p>
<p class=MsoNormal><span style='color:#1F497D'>H.225.0 messages are quite
different.<o:p></o:p></span></p>
<p class=MsoNormal><span style='color:#1F497D'>Q.931 status codes cover syntax
errors in Q.931 part of the message. However, very significant part of the
H.225.0 <o:p></o:p></span></p>
<p class=MsoNormal><span style='color:#1F497D'>is PER encoded, so “is the
perfectly encoded Q.931 message with ASN.1 part encoded incorrectly encoded
correctly?” <o:p></o:p></span></p>
<p class=MsoNormal><span style='color:#1F497D'>and should the response be
STATUS and if STATUS then with which cause code?<o:p></o:p></span></p>
<p class=MsoNormal><span style='color:#1F497D'><o:p> </o:p></span></p>
<p class=MsoNormal><span style='color:#1F497D'>I believe it does not make sense
to respond to syntactical errors in Q.931 part and ignore such errors in ASN.1.
<o:p></o:p></span></p>
<p class=MsoNormal><span style='color:#1F497D'>On the other hand we did not
have and do not have any fine grained definition of what to do with different
ASN.1 error cases <o:p></o:p></span></p>
<p class=MsoNormal><span style='color:#1F497D'>and this most probably created
the situation where different implementations behave differently. <o:p></o:p></span></p>
<p class=MsoNormal><span style='color:#1F497D'><o:p> </o:p></span></p>
<p class=MsoNormal><span style='color:#1F497D'>BTW: In our implementation for
example we use cause value 95: “Invalid message, unspecified” for
any syntactical mistake <o:p></o:p></span></p>
<p class=MsoNormal><span style='color:#1F497D'>in any H.225.0 message. <b>If
somebody has a different approach</b>, please share with us!<o:p></o:p></span></p>
<p class=MsoNormal><span style='color:#1F497D'><o:p> </o:p></span></p>
<p class=MsoNormal><span style='color:#1F497D'>So my ultimate goal is to make
clear that H.323 is not working according to ETSI TS 101 804 – 2 and at
the same to create minimal <o:p></o:p></span></p>
<p class=MsoNormal><span style='color:#1F497D'>possible impact on existing
implementations. <o:p></o:p></span></p>
<p class=MsoNormal><span style='color:#1F497D'><o:p> </o:p></span></p>
<p class=MsoNormal>Regards,<o:p></o:p></p>
<p class=MsoNormal>Sasha<o:p></o:p></p>
<p class=MsoNormal><o:p> </o:p></p>
<p class=MsoNormal><o:p> </o:p></p>
<p class=MsoNormal><span style='color:#1F497D'><o:p> </o:p></span></p>
<p class=MsoNormal><span style='color:#1F497D'><o:p> </o:p></span></p>
<div>
<div style='border:none;border-top:solid #B5C4DF 1.0pt;padding:3.0pt 0in 0in 0in'>
<p class=MsoNormal><b><span style='font-size:10.0pt;font-family:"Tahoma","sans-serif"'>From:</span></b><span
style='font-size:10.0pt;font-family:"Tahoma","sans-serif"'> Paul E. Jones
[mailto:paulej@packetizer.com] <br>
<b>Sent:</b> Friday, October 02, 2009 2:29 PM<br>
<b>To:</b> Sasha Ruditsky; itu-sg16@lists.packetizer.com<br>
<b>Subject:</b> RE: [itu-sg16] AVD-3813 Handling Of Error Conditions in H.323<o:p></o:p></span></p>
</div>
</div>
<p class=MsoNormal><o:p> </o:p></p>
<p class=MsoNormal><span style='color:#1F497D'>Sasha,<o:p></o:p></span></p>
<p class=MsoNormal><span style='color:#1F497D'><o:p> </o:p></span></p>
<p class=MsoNormal><span style='color:#1F497D'>The fact that H.225.0 says a
device shall send a Status message for an unknown message, yet leaves the Cause
code unspecified, is certainly an issue we should close on. My suggestion
would be to use 97: “Message type non-existent or not<o:p></o:p></span></p>
<p class=MsoNormal><span style='color:#1F497D'>Implemented.”<o:p></o:p></span></p>
<p class=MsoNormal><span style='color:#1F497D'><o:p> </o:p></span></p>
<p class=MsoNormal><span style='color:#1F497D'>I think an “unknown
message” would be one that is not currently defined today in
H.225.0. If the message is syntactically invalid, then I believe that is
a protocol error. In that case, either 100 or 111 would be good choices
depending on whether it is just an invalid IE or something that is impossible
to decode.<o:p></o:p></span></p>
<p class=MsoNormal><span style='color:#1F497D'><o:p> </o:p></span></p>
<p class=MsoNormal><span style='color:#1F497D'>Those are fairly minor changes,
though the impact might be significant. However, your problem description
suggests you are looking for a broader statement. Do you have a specific
proposal in mind, either a new paragraph or section on error handling or a
reference to Q.931?<o:p></o:p></span></p>
<p class=MsoNormal><span style='color:#1F497D'><o:p> </o:p></span></p>
<p class=MsoNormal><span style='color:#1F497D'>Paul<o:p></o:p></span></p>
<p class=MsoNormal><span style='color:#1F497D'><o:p> </o:p></span></p>
<div style='border:none;border-left:solid blue 1.5pt;padding:0in 0in 0in 4.0pt'>
<div>
<div style='border:none;border-top:solid #B5C4DF 1.0pt;padding:3.0pt 0in 0in 0in'>
<p class=MsoNormal><b><span style='font-size:10.0pt;font-family:"Tahoma","sans-serif"'>From:</span></b><span
style='font-size:10.0pt;font-family:"Tahoma","sans-serif"'>
itu-sg16-bounces@lists.packetizer.com
[mailto:itu-sg16-bounces@lists.packetizer.com] <b>On Behalf Of </b>Sasha
Ruditsky<br>
<b>Sent:</b> Wednesday, September 30, 2009 6:01 PM<br>
<b>To:</b> itu-sg16@lists.packetizer.com<br>
<b>Subject:</b> [itu-sg16] AVD-3813 Handling Of Error Conditions in H.323<o:p></o:p></span></p>
</div>
</div>
<p class=MsoNormal><o:p> </o:p></p>
<p class=MsoNormal>Q2 Experts,<o:p></o:p></p>
<p class=MsoNormal><o:p> </o:p></p>
<p class=MsoNormal>The conclusion for the discussion of the AVD-3813 during the
last SG16 meeting’s was to ask the experts opinion through the mailing
list.<o:p></o:p></p>
<p class=MsoNormal>My apology for the short notice. I hope that we still have
time before the next meeting for people to understand the problem and express
their opinions. <o:p></o:p></p>
<p class=MsoNormal><o:p> </o:p></p>
<p class=MsoNormal>The problem discussed in AVD 3813 is more or less as
follows:<o:p></o:p></p>
<p class=MsoNormal><o:p> </o:p></p>
<p class=MsoNormal>“<o:p></o:p></p>
<p class=MsoNormal>H.225.0 gives very little attention to the specification of
processing of the H.225.0 Call Signaling messages errors. The only place dedicated
to this subject is Clause 7.1 of H.225.0. <o:p></o:p></p>
<p class=MsoNormal><o:p> </o:p></p>
<p class=MsoNormal>On the other hand, ITU-T Recommendation Q.931 on which
H.225.0 messages are based provides quite detailed information on the same
subject. While H.225.0 states that Implementations shall follow ITU-T Rec.
Q.931 as specified in H.225.0, there is a lot of confusion surrounding the
cases which H.225.0 does not cover and Q.931 does.<o:p></o:p></p>
<p class=MsoNormal><o:p> </o:p></p>
<p class=MsoNormal>In addition, ETSI TS 101 804 – 2 defines Conformance
Test Specification for ITU-T H.225.0. This test specification apparently based
on Q.931 procedures, not on the corresponding H.225.0 ones. More than this, in
many cases ETSI TS 101 804 – 2 requests behavior which claims to be based
on Q.931, however is not defined neither in Q.931, nor H.225.0. <o:p></o:p></p>
<p class=MsoNormal>“<o:p></o:p></p>
<p class=MsoNormal><o:p> </o:p></p>
<p class=MsoNormal>Apparently “H.323 conformant” not always means
“ETSI TS 101 804 – 2 conformant” and I believe we need to
find some solution to at least make this particular point clear.<o:p></o:p></p>
<p class=MsoNormal><o:p> </o:p></p>
<p class=MsoNormal>I’m going to resubmit AVD-3813. <o:p></o:p></p>
<p class=MsoNormal>It would be great to be able to get some ideas from the
group into the resubmitted document.<o:p></o:p></p>
<p class=MsoNormal><o:p> </o:p></p>
<p class=MsoNormal>Thank you,<o:p></o:p></p>
<p class=MsoNormal>Sasha <o:p></o:p></p>
<p class=MsoNormal><o:p> </o:p></p>
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