Relationship of H.323 and H.245 versions

[Chris Purvis]

Paul (and others),

Consider the case of a v1 gatekeeper routing H.225.0 and NOT H.245 in a call
between two v2 endpoints.  The gatekeeper certainly MAY relegate the H.225.0
messages to v1.  This may be a policy decision, or it may be due to stack
capabilities.  Note that the gatekeeper may not always desire to relay
messages entirely transparently, and is entirely within its rights to make
this sort of alteration (although people writing H.323 stacks for
gatekeepers would probably be well advised to implement relaying of messages
or message fragments).  Certainly the standard should not mandate that
message relay should be entirely transparent.  Anyway, the upshot of this is
that all H.225.0 messages in the call will be relegated to v1 by the
gatekeeper.  The H.245 session runs directly end-to-end and will hence be
version 3, so both endpoints in the call need to be able to cope with an
H.245 session of a different version from that implied by the H.225.0
session.

Similar discrepancies may occur in the opposite direction (later version of
H.225.0 than H.245) for similar, but marginally more complex reasons.

So what do we gain by insisting on an endpoint supporting EXACTLY version 3
of H.245 if it happens to be EXACTLY version 2 of H.225.0 and vice versa?
Although I agree that it is what is currently specified I'm unconvinced it
buys us anything.

Regards,
Chris

> -----Original Message-----
> From: Paul Long [mailto:Plong at SMITHMICRO.COM]
> Sent: 29 January 1999 8:09
> To: ITU-SG16 at MAILBAG.INTEL.COM
> Subject: Re: Relationship of H.323 and H.245 versions
>
>
> Gary,
>
> You be the judge:
>
> Summary/H.323v2: "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). Version 2
> products can be
> identified by H.225.0 messages containing a
> protocolIdentifier = {itu-t (0)
> recommendation (0) h (8) 2250 version (0) 2} and H.225.0
> messages containing a
> protocolIdentifier = {itu-t (0) recommendation (0) h (8) 245
> version (0) 3}."
>
> Assuming this text is normative, H.323v2 uses H.225.0v2 and
> H.245v3. Period.
>
> IMO, we will be asking for big trouble if we at some point
> decide that one can
> mix and match versions and even use subsets or supersets of a
> particular
> version. Whatever interoperability problems we have now will
> be magnified many
> times over if we head down that slippery slope.
>
> Paul Long
> Smith Micro Software, Inc.
>
>         -----Original Message-----
>         From:   Gary A. Thom [SMTP:gthom at DELTA-INFO.COM]
>         Sent:   Friday, January 29, 1999 1:37 PM
>         To:     ITU-SG16 at MAILBAG.INTEL.COM
>         Subject:        Re: Relationship of H.323 and H.245 versions
>
>         One more question????
>
>
>         > Dave,
>         >
>         > Sorry, but I won't be in Monterey.
>         >
>         > I agree with what you say, except that I would go
> further and state
> that there
>         > is always a one-to-one mapping between H.225.0 and H.245
> protocolIdentifiers
>         > via H.323. For example,
>         >
>         >     H.225.0v1 => H.323v1 => H.245v2 and H.245v2 =>
> H.323v1 =>
> H.225.0v1
>         >     H.225.0v2 => H.323v2 => H.245v3 and H.245v3 =>
> H.323v2 =>
> H.225.0v2
>         >
>         > This is already implied by the Summary section of
> H.323 starting
> with version
>         > 2. I think it's clear, but you could add
> clarification text if you
> like. IOW,
>         > for example, an EP cannot use H.245v2 and H.225.0v2
> in the same
> call.
>         >
>
>         But can H.225.0 V2 (H.323 V2) and H.245V4 (or 5) be
> used in the same
> call???
>
>         Gary
>
>         ------------------------------------------------------
>         Name   : Gary A. Thom
>         Company: Delta Information Systems, Inc.
>         Address: 300 Welsh Rd., Bldg 3
>                  Horsham, PA 19044 USA
>         Phone  : +1-215-657-5270         Fax : +1-215-657-5273
>         E-mail : gthom at delta-info.com
>         ------------------------------------------------------
>