ASN.1 Syntax of H.245

mike.nilsson at BT.COM mike.nilsson at BT.COM
Tue Aug 31 05:23:41 EDT 1999

An error has been found in the ASN.1 syntax of H.245 version 5. Thanks to
Jaakko Helanti and Paul Long for identifying it.

The error occurs in the section given below where the word 'OPTIONAL' should
appear at the end of the line 'genericModeParameters    GenericCapability'.
This was an editorial error, but one that has some technical consequence.
Although the absence of the word 'OPTIONAL' does not change the
understanding of bits received by a decoder, it does demand that an encoder
always send the information 'genericModeParameters'. This was not the
intention and is not desirable.

ModeElement     ::= SEQUENCE
        type            CHOICE
                nonStandard     NonStandardParameter,
                videoMode       VideoMode,
                audioMode       AudioMode,
                dataMode        DataMode,
                encryptionMode  EncryptionMode,
                h235Mode        H235Mode

        h223ModeParameters      H223ModeParameters OPTIONAL,
        v76ModeParameters       V76ModeParameters OPTIONAL,
        h2250ModeParameters     H2250ModeParameters OPTIONAL,
        genericModeParameters   GenericCapability


I have contacted the ITU regarding this. Their response was that if there is
consensus, as determined by e-mail, then as version 5 (05/99) of H.245 has
not yet been published, it will be possible to correct this error before

I hope that two weeks will be enough time for everyone to consider this
issue, and so aim to respond to the ITU on 13 September about whether we
have achieved consensus to make this correction.

Best regards

Mike Nilsson

* Mike Nilsson                           Tel:   +44 1473 645413      *
* Applications Technology Group          Fax:   +44 1473 645011      *
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