TPKT in H.225.0

Greg Goodknight ggoodkni at
Fri Mar 5 14:44:54 EST 1999

> H.323v2, section 6.7:
> "The MCU is an endpoint which provides support for multipoint conferences.
> The MCU shall consist of an MC and zero or more MPs."
> Note that the phrase used is "consist of", not "contain".  If an MCU is an
> endpoint, it is callable (I think we're agreed on that).  If it consists of
> an MC and zero or more MPs, that means it must still be callable when it
> consists of only an MC.  Therefore the MC is the part of an MCU that is
> callable.  Hence an MC MAY be a callable entity.

While your logic may be correct (in a round about way), the fact is that the original intention is
that the MC is not a callable entity. An MCU which only contains an MC is a callable entity.

> The wider point is that my understanding was that all control signalling
> done by an MCU was done by the MC part of it (again on the basis of those
> two sentences).
> If this is inconsistent with other parts of the standard, then it certainly
> needs to be fixed (please give references); if it is consistent with the
> rest of the standard, but not what was intended, then we need to reconsider
> what we really want.

All of the signalling of an MCU is not done by the MC. The MC is only responsible for coordinating
the the operating mode of the participants, and opening and closing logical channels for media
streams. It does this through the H.245 channel.

Any other singalling functions performed by the MCU (such as ARQ, setup, etc) are done by other
unspecified (or un-named) control elements in the MCU (just as those un-named control elements
perform that function in a terminal).

> For the case under discussion I'd agree with Gary that it's a minor semantic
> quibble (and as such I was planning to allow Gary's mail on its own to pass
> without comment), but if there's the possibility of it becoming more than
> that maybe we ought to clear it up.

As I said, this was the original intention. Since very few original intentions exist in H.323
today, maybe this also needs to be revisited.


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

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