Relationship of H.323 and H.245 versions

Chris Purvis CPurvis at MADGE.COM
Thu Jan 14 10:56:12 EST 1999


The answer to your direct question is, I believe, a) - but I don't see why
it needs to be.

In some senses an H.323 version is defined by a combination of an H.225.0
version and an H.245 version.  You may or may not discover the second of
these pieces of information from another endpoint, in particular if you're
using faststart (it seems only to be communicated in a terminalCapabilitySet
message).  How you'd discover an H.323 version by any other means I don't

There's also the issue that when people say they support version n, they do
not necessarily mean that they support ALL the features of that version (it
generally simply means that all the ASN.1 is there); also there may be cases
where different signalling channels follow different routes (eg a version 28
gatekeeper or proxy routing a version 1 endpoint's (or vice versa) H.225 but
not H.245) - so it's dangerous to make assumptions on the basis of knowledge
of another party's version.

Is there something particular that you're trying to achieve?  If there's a
reason for it, we need to think about how to put more versioning information
in to the standards.

I'd add the further question: Is there any point at which we can assume
support of some of the H.450 supplementary services?  Or H.235 security?  I
doubt it...


> -----Original Message-----
> From: Pete Cordell [mailto:pete.cordell at BT-SYS.BT.CO.UK]
> Sent: 14 January 1999 2:59
> Subject: Relationship of H.323 and H.245 versions
> Gary,
> As H.323 editor can you comment on which of the following
> statements is
> more correct:
> a) H.323 version 2 can be used with H.245 version 3 ONLY
> b) H.323 version 2 can be used with H.245 version 3 OR LATER.
> My view is that it is undesirable to have to up-issue H.323 to a new
> version if all you want to do is make use of new features in H.245.
> Also, as part of third party re-routing, in the future it may
> occur that
> an H.323 version 3 endpoint originally connected to another H.323
> version 3 endpoint will end up being connected to the H.245 from an
> H.323 version 2 endpoint.  Hence assuming that the H.323 and H.245
> versions are locked together does not work.  However, I'm not sure if
> this aligns with the groups understanding.  Do you have any comments?
> Regards,
> Pete
> =================================
> Pete Cordell
> BT Labs
> E-Mail: pete.cordell at
> Tel: +44 1473 646436
> Fax: +44 1473 645499
> =================================

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