T.38 potentially broken by recent Corrigendum

Dominic Walker dominic.walker at NORTELNETWORKS.COM
Fri Mar 14 10:54:46 EST 2003


FYI, we are currently discussing the issue within the Q.14 e-mail reflector,
and the Q.14 experts are looking at a one possible solution that may link a
version number to the support of the two  ASN.1 version.With this mechanism,
version 0 (and possibly version 1) would refer to the ASN.1 definition
published in the 06/1998 T.38 spec, and version 2 or higher would  refer to
the ASN.1 definition published in the 03/2002 T.38 spec. I believe a
decision will be made at the Q.14  May 2003 Geneva meeting. 
Dominic.

-----Original Message-----
From: Boyle, Kevin [NCRTP:3Z40:EXCH] 
Sent: Friday, March 14, 2003 2:16 PM
To: ITU-SG16 at echo.jf.INTEL.COM
Subject: Re: T.38 potentially broken by recent Corrigendum


All,
 
It is my understanding that the ellipsis was intended to be there, and that
it wasn't until folks started implementing that it was noticed that it got
dropped somewhere between the editor's hands and publication. There was a TD
in the Feb 2000 meeting noting this typo.  I can produce it if anyone wants
to see it.
 
It is also my understanding that care was taken to ensure that all known
vendors were made aware of the change at the time.
 
Kevin

-----Original Message-----
From: Klaghofer Karl ICN EN HS D 11 [mailto:karl.klaghofer at SIEMENS.COM] 
Sent: Friday, March 14, 2003 3:44 AM
To: ITU-SG16 at echo.jf.INTEL.COM
Subject: AW: T.38 potentially broken by recent Corrigendum


Paul,
 
I fully agree with you, that the T.38 (1998) asn.1 and the Revision of T.38
(2002) asn.1 needs to be backwards compatible. 
 
Regards,
Karl Klaghofer
Siemens

-----Ursprüngliche Nachricht-----
Von: Paul E. Jones [mailto:paulej at PACKETIZER.COM]
Gesendet: Montag, 3. März 2003 03:21
An: ITU-SG16 at echo.jf.INTEL.COM
Betreff: T.38 potentially broken by recent Corrigendum



Folks,
 
I just recently discovered that the ITU-T published a corrigendum to T.38
(1998) that apparently breaks backward compatibility for all T.38 devices
currently deployed that follow the original 1998 specifications.  The
particular document in question is Corrigendum 1, which was approved in 2000
and subsequently published in May 2001.  You can download the corrigendum
document for free from this site:
http://www.itu.int/rec/recommendation.asp?type=folders
<http://www.itu.int/rec/recommendation.asp?type=folders&lang=e&parent=T-REC-
T.38> &lang=e&parent=T-REC-T.38 
 
The issue at hand is a change in the ASN.1 syntax found in Annex A/T.38.
The particular data structure is shown here:
 

Data-Field ::= SEQUENCE OF SEQUENCE
{
    field-type ENUMERATED
    {
        hdlc-data,
        hdlc-sig-end,
        hdlc-fcs-OK,
        hdlc-fcs-BAD,
        hdlc-fcs-OK-sig-end,
        hdlc-fcs-BAD-sig-end,
        t4-non-ecm-data,
        t4-non-ecm-sig-end,
        ...
    },
    field-data OCTET STRING (SIZE(1..65535)) OPTIONAL
}
 

The syntactical change was the addition of an ellipsis at the end of the
ENUMERATED "field-type".  In the published 1998 specification, this ellipsis
did not exist.
 
What I would like to know is whether this change impacts your product or
not.  I am aware of many deployed devices on the market today that employs
the 1998 syntax without this ellipsis.  I would like to find out to what
extent this change is going to present problems for companies represented on
various lists and, if I get sufficient support, I want to take a
contribution to the ITU-T SG16 meeting in May to try to resolve this problem
in such a way as to not break backward compatibility and interoperability.
 
I am looking forward to your replies.
 
Kindest Regards,
Paul E. Jones
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