ASN.1 Syntax of H.245

Pete Cordell pete at TECH-KNOW-WARE.COM
Tue Aug 31 08:02:17 EDT 1999


I agree that this change has to be made.  The original form makes no sense
and, once pointed out, is clearly defective.

As you say, it will NOT affect the bits on the wire.  Indeed, depending on
the compiler you have, you can almost get away without changing any code you
have written (although re-compiling and tweaking would be advised).

Well spotted Jaakko and Paul.


Pete Cordell
pete at

-----Original Message-----
From: mike.nilsson at BT.COM <mike.nilsson at BT.COM>
Date: 31 August 1999 10:52
Subject: ASN.1 Syntax of H.245

>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'
>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
>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      *
>* Internet and Multimedia Applications   Email: mike.nilsson at  *
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