Relationship of H.323 and H.245 versions

Pete Cordell pete.cordell at BT-SYS.BT.CO.UK
Wed Jan 20 14:49:36 EST 1999


Comments interleaved...
>I understand what you're trying to do, but I'm a little concerned
>about allowing a v2 entity to support any version of H.245,
>including unspecified future versions which may or may not be
>compatible with what we have now.
As an ITU requirement any future H.245 version must be backward
compatible with an earlier one so this shouldn't (in theory) be an
>So let me propose the following paragraph as replacement text for
>the offending portion of the H.323 Version 2 Summary section (which
>begins in the same way).
One reason for suggesting new text is that I wanted a fairly definitive
statement on this issue and the summary doesn't seem the right place for
such normative text (i.e. it's a summary and everything it says should
be in the main body of the document and so doesn't have any normative
value by itself).  However, if the text you describe were copied to a
normative part of the document, subject to changing 'other versions' to
'more recent versions' (as I have attempted to indicate below) I would
be happy.  (Also I would like to add a note that the version of H.245
that they end up connected to may change as a call evolves, as it seems
churlish not to mention a particular gotcha if we know about it.  I've
attempt to add text for this below.)

>"Products claiming compliance with Version 2 of H.323 shall comply
>with all of the mandatory requirements of this document, H.323 (1998),
>which references H.225.0 (1998) and H.245 (1998).  The protocol
>identifiers used in messages defined in H.225.0 (1998) and H.245
>(1998) are specified in those recommendations.  An H.323 Version 2
>compliant product may also be compliant with (other)->(more recent) versions
>of these
>recommendations, but should not send messages or invoke procedures
>defined in a newer version of a recommendation than a peer has
identified itself as supporting.  () ->(Implementations must also be
aware that, due to the procedures for 'Third party initiated pause and
re-routing,' they may be connected to different versions of H.245 at
>different times during the life of a call.)"
>Dave Walker
>Mitel Corporation
>Ontario, CANADA



Pete Cordell
BT Labs
E-Mail: pete.cordell at
Tel: +44 1473 646436
Fax: +44 1473 645499

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