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<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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