Subject: Receiving ATM SETUP message at the MG

From: CORNELY Thomas CNET/DAC/ISS <[email-masked]>
Date: Fri, 26 Nov 1999 14:51:35 +0100

Hi Brian, 
 
This question was raised by the work currently going on in ITU-T on Q.BICC
(I'm sure you've heard of it). As you probably know, the first release of
BICC (which should be determined in 2 weeks) supports only ATM at what ITU-T
calls "BCF" (i.e. MG in Megaco parlance). They also have defined a BNC-ID
used to correlate between the Q.BICC messages used for Call Setup and the
ATM Signalling messages used for Connection Setup. The BNC-ID is included in
ATM SETUP messages and supposedly used for correlation upon reception of the
SETUP.
 
Looking at the BICC Call Flows, and anticipating the fact we will want to
use Megaco/H.248 between CSF and BCF (MGC/MG), I am wondering what an MG is
supposed to do when it receives an ATM SETUP message :
Is it supposed to reply with a CONNECT, and create an ATM termination by
itself? In that case, in what context is this ATM termination put? Is a new
context automatically created on reception of the SETUP message or is the
ATM termination put in the NULL context, while the MG waits for instructions
from the MGC?
 
In the case of BICC backward call setup flows, the MG which receives the ATM
SETUP message already contains the "Context" where this ATM termination
should be put. Unfortunately, the only way the MG could know where to
include the ATM Termination would be by using the BNC-ID included in the
SETUP message... Is that something an MG should be able to do (considering
it knows the different BNC-IDs it may receive), or should such correlation
work only be done by an MGC?
Thanks in advance for your help.
 
Thomas.
_______________________________________________________ 

Thomas Cornély 
mailto:[email-masked]
<mailto:[email-masked]>  

France Telecom - Cnet 
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29 31 42 
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_______________________________________________________

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From: Stephen Terrill <[email-masked]>
Date: Mon, 29 Nov 1999 09:19:55 +0100

Hi Thomas,

I see that you are preparing for this week.  I suggest you seek out one of my collegues there, Christian Groves (you will find him hanging around with Leslie Graf), and he should be able to explain some things further.

Anyway, to answer your questions, if you look at the information flows produced in the requirements group (Q 6/11), it shows that the BNC-id comes from the BCF which will terminate the ATM SETUP (or IAM) message (Note that this is true for both the forward and backwards bearer establishement).  It is significant that the BCF generates the BNC-id before the ATM SETUP is recieved.  The BICC signalling transfers this to the CSF of the serving node which will originate the ATM SETUP message via the APM mechanism.  That CSF will request the BCF to orignate the ATM SETUP message with the BNC-id.

H.248 can be used between the CSF and the BCF to create a termination at the BCF which will terminate the ATM SETUP message, and the BNC-id returned to the corresponding CSF the BNC-id as a "property" of the termination.  This would be an "emphemeral termination", and when the SETUP message is received into that BCF, the correct termination is identified by the BNC-id.  Thus, the correlation is performed in the "BCF" at the reception of the ATM SETUP message to a value which has already been generated for this purpose (BNC-id).  At the Serving Node which will originate the ATM SETUP message, the CSF can use H:248 to request the BCF to initate the ATM SETUP message with the BNC-id, the property mechanism can be used for this.

In addition, it is worth noting that BICC is striving for "Bearer Independance", as such the interface between the CSF and the BCF should not be specific to ATM.  It is worth noting that H.248 could also be used between the BCF and the "port function", however this interface will be specific to the port technology.

I hope that this helps, and have a good meeting.

Regards,

..//Steve