Hi Paul,
Yes, I am looking for a Broader
statement.
Specifically, my problem is the
fact that ETSI TS 101 804 – 2 defines procedures referring to Q.931
sections.
Let consider one example from ETSI
TS 101 804 – 2:
BCC_TE_S_U00_07
clause 5.8.6.1 [4]
Ensure that the
IUT in the Null call state U0, on receipt of a SETUP message with a mandatory
information element
missing,
sends a RELEASE
COMPLETE message containing a Cause information element indicating the cause
value 96
"mandatory
information element missing" and remains in the Null call state U0.
Which suggest to the reader that
Q.931 section 5.8.6.1 (and some other explicitly referenced sections)
is the way H.323 should be
implemented.
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,
that these sections do not
apply, instead… and here we do need to provide something which would
close the gap created by this
unspecified Cause code value.
The problem to select such cause
is stemmed from the fact that syntax of Q.931 messages and syntax of
H.225.0 messages are quite
different.
Q.931 status codes cover syntax
errors in Q.931 part of the message. However, very significant part of the
H.225.0
is PER encoded, so “is the
perfectly encoded Q.931 message with ASN.1 part encoded incorrectly encoded
correctly?”
and should the response be STATUS
and if STATUS then with which cause code?
I believe it does not make sense
to respond to syntactical errors in Q.931 part and ignore such errors in ASN.1.
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
and this most probably created
the situation where different implementations behave differently.
BTW: In our implementation for
example we use cause value 95: “Invalid message, unspecified” for
any syntactical mistake
in any H.225.0 message. If
somebody has a different approach, please share with us!
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
possible impact on existing
implementations.
Regards,
Sasha
From: Paul E. Jones
[mailto:paulej@packetizer.com]
Sent: Friday, October 02, 2009 2:29 PM
To: Sasha Ruditsky; itu-sg16@lists.packetizer.com
Subject: RE: [itu-sg16] AVD-3813 Handling Of Error Conditions in H.323
Sasha,
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
Implemented.”
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.
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?
Paul
From:
itu-sg16-bounces@lists.packetizer.com
[mailto:itu-sg16-bounces@lists.packetizer.com] On Behalf Of Sasha
Ruditsky
Sent: Wednesday, September 30, 2009 6:01 PM
To: itu-sg16@lists.packetizer.com
Subject: [itu-sg16] AVD-3813 Handling Of Error Conditions in H.323
Q2 Experts,
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.
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.
The problem discussed in AVD 3813 is more or less as
follows:
“
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.
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.
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.
“
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.
I’m going to resubmit AVD-3813.
It would be great to be able to get some ideas from the
group into the resubmitted document.
Thank you,
Sasha