T.38 potentially broken by recent Corrigendum

Paul E. Jones paulej at PACKETIZER.COM
Sun Mar 2 21:20:46 EST 2003


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&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,

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Paul E. Jones
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