Subject: [Megaco] precise identification of an incoming call

From: Raphael Tryster <[email-masked]>
Date: Mon, 7 Jan 2002 14:02:59 +0200

In the example call flow given in RFC 3015 Appendix A, the incoming call to
the second subscriber begins with an ADD command from MGC to MG2 in step 14.
Is this the only way an incoming call can begin?  In other words, can the MG
assume the MGC will not send it any other commands related to an incoming
call before the ADD?

Raphael Tryster

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From: "Tom-PT Taylor"<[email-masked]>
Date: Mon, 7 Jan 2002 09:21:27 -0500

You may be correct, but my agreement is because no counter-examples come
immediately to mind.  I wouldn't design equipment on this assumption.  There
may be some call flow where it makes sense to modify the second subscriber's
termination while it is still in the null context.

-----Original Message-----
From: Raphael Tryster [mailto:[email-masked]]
Sent: Monday, January 07, 2002 7:03 AM
To: [email-masked]
Subject: [Megaco] precise identification of an incoming call

Raphael Tryster 

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From: "Tom-PT Taylor"<[email-masked]>
Date: Mon, 7 Jan 2002 09:21:27 -0500

-----Original Message-----
From: Raphael Tryster [mailto:[email-masked]]
Sent: Monday, January 07, 2002 7:03 AM
To: [email-masked]
Subject: [Megaco] precise identification of an incoming call

Raphael Tryster

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From: "Rosen, Brian" <[email-masked]>
Date: Mon, 7 Jan 2002 09:39:57 -0500

I second this.  DO NOT assume anything.

The question itself makes me nervous.  In general, the MG is a slave,
and slaves never make assumptions about anything.  The MG should
not even have any notion of a "call".  It only deals with
events, signals, properties, and streams of media.

Brian

> From: Tom-PT Taylor [mailto:[email-masked]]
> Sent: Monday, January 07, 2002 9:21 AM
> To: 'Raphael Tryster'; [email-masked]
> Subject: RE: [Megaco] precise identification of an incoming call
> 
>

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From: "Rosen, Brian" <[email-masked]>
Date: Mon, 7 Jan 2002 09:39:57 -0500

Brian

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From: Al Varney <[email-masked]>
Date: Mon, 07 Jan 2002 09:37:05 -0600

>>assume the MGC will not send it any other commands related to an incoming

    Given the low-level, device-control nature of MEGACO/H.248, I've found 
it easier to understand MG functionality by assuming the MG knows nothing 
about "calls".  An MG is a device for making connections -- a higher layer 
(the MGC) is where the concept of calls beginning/ending or 
incoming/outgoing takes place.  You could even imagine applications where 
MEGACO is used to control non-call-related connections (Public Address 
announcements, for example).

    Rephrased in connection terms, you could ask if any commands related to 
a new connection (in or out) occurs prior to an ADD.  The answer to that 
requires defining when a "connection" begins to exist; that is, can a 
connection exist prior to ADD?  If it can, then presumably some non-ADD 
command created it.  (Move from another context would not be a "new" 
connection.)

    Back to your call-level question (commands before ADD):  Well, the 
whole notify/event mechanism could occur multiple times in the null context 
before a "connection" is created.  An incoming call might have only an 
outgoing connection (MG-based dial tone on an ISDN B-channel connection) at 
the beginning of an incoming ISDN voice call.  An IP Phone might have some 
local signal (dial tone) turned on via MEGACO prior to a connection being 
ADDed (although ADDing early would be a way to reserve resources for the 
call).  I think it likely other pre-ADD scenarios exist.

    This is just my own opinion and my attempt at trying to keep 
"device-control" protocols separated from "call-control" protocols.  It 
could be all wrong.  I do know it's been difficult trying to avoid thinking 
in terms of "calls".

Al Varney

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From: Al Varney <[email-masked]>
Date: Mon, 07 Jan 2002 09:37:05 -0600

Al Varney