Megaco File Repository -- Addition Of Sample Call Flows

Tom-PT Taylor taylor at NORTELNETWORKS.COM
Tue Apr 3 14:52:41 EDT 2001


It is absolutely true that the other endpoint shall send its capability set
before acknowledging the received set.  ACKing a received set before sending
its own will break the H.323v4 procedure of doing H.245 in parallel with
Fast Connect.

Other things that might fail include master/slave determination.  Many
endpoints (particularly those that have no chance of being the MC of a
conference) will send the MSDet message at the same time as the TCS.  It is
also possible to send other H.245 commands before waiting for the TCS
response (perhaps the multipoint mode command or something like that if the
endpoint is already the MC of a multipoint conference).


----- Original Message -----
From: "Frank Derks" <frank.derks at PHILIPS.COM>
To: <ITU-SG16 at mailbag.cps.INTEL.COM>
Sent: Tuesday, April 03, 2001 11:32 AM
Subject: What does 'exchange' mean and which H.245 message gets to be sent

> H.323 talks about capability exchange, but it is not clear
> to me whether exchange really means that communicating endpoints
> send their capability sets to _each other_ or that one endpoint
> sends its capability set. An example of this can be found in the
> below text. It talks about succesfully completing capability
> exchange, but does this means that the initiating endpoint has
> sent its capability set and that this was acknowledge by the
> receiver or does it mean that it has also received the capability
> set of the other party?
> 8.2/H.323 states:
> "Endpoint system capabilities are exchanged by transmission
> of the H.245 terminalCapabilitySet message. This capability
> message shall be the first H.245 message sent unless the
> endpoint is indicating that it understands the
> parallelH245Control field (see section 8.2.4). If prior to
> successful completion of terminal capability exchange, any
> other procedure fails, (i.e. rejected, not understood, not
> supported) then the initiating endpoint should initiate and
> successfully complete terminal capability exchange before
> attempting any other procedure. "
> The second sentence mandates that the terminalCapabilitySet
> message be the first message sent (given that
> "parallelH245Control" is not used). Which "failing procedures"
> are then being referred to in the third sentence?
> If terminalCapabilitySet has to be the first message to be
> sent, does this mean that an endpoint that has not sent a
> terminalCapabilitySet message yet and receives this message,
> it first has to send a terminalCapabilitySet message before
> acknowledging the received capability set?
> Frank
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