Error in H.323v3 ASN.1

Paul Long Plong at SMITHMICRO.COM
Fri Oct 6 11:58:36 EDT 2000


Bancroft,

These components are in a CHOICE type, so the clause that you specify has
nothing to do with our discussion. I think your response assumes they are in
a SEQUENCE type.

Also, by "do not use," I meant that, upon receipt, these choices are to be
semantically treated as another, generic choice, undefinedReason and that
they are to no longer be transmitted. Again, these are CHOICE, not SEQUENCE
components.

Paul Long
Smith Micro Software, Inc.

-----Original Message-----
From: Bancroft Scott [mailto:baos at OSS.COM]
Sent: Friday, October 06, 2000 4:17 AM
To: ITU-SG16 at MAILBAG.INTEL.COM
Subject: Re: Error in H.323v3 ASN.1


On Thu, 5 Oct 2000, Paul Long wrote:

<snip>

Unless I am misunderstanding what you are saying, the "-- do not use"
will
not work if the receiver is using an earlier version in which the "-- do
not use" type is defined, for it violates X.680 clause 24.14:

   24.14 A value for a given extension addition type shall not be
   specified unless there are values specified for all extension
addition
   types not marked OPTIONAL or DEFAULT that lie logically between the
   extension addition type and the extension root.

   NOTE 1 -Where the type has grown from the extension root (version 1)
   through version 2 to version 3 by the addition of extension
additions,
   the presence in an encoding of any addition from version 3 requires
the
   presence of an encoding of all additions in version 2 that are not
   marked OPTIONAL or DEFAULT.

Omitting OPTIONAL and DEFAULT from an extension addition definition
means
that an extension addition value is mandatory in messages that are
originated by an implementation in which such extension additions are
defined, which implies that an encoding cannot have a missing mandatory
extension addition value followed by any other component.

The only way that interoperability can be achieved here is by the older
version H.225 spec being changed to add OPTIONAL to those items marked
with "-- do not use".  It will have no effect on the bits on the wire,
other than to make such encodings valid.

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