Subject: RE: [Megaco] H.248 equivalent of MGCP Delete from MG

From: "Rosen, Brian" <[email-masked]>
Date: Tue, 14 Aug 2001 11:40:37 -0400

The basic answer is that there is no equivalent to delete from MG to MGC,
and this was a very conscious design decision.
 
The model is that the MGC is ALWAYS in control of the context.  The MG
reports
status information with errors or Notifies, and the MGC does the Subtract.
This avoids a lot of race conditions, and out-of-sync situations.
 
Brian

-----Original Message-----
From: David Barr [mailto:[email-masked]]
Sent: Tuesday, August 14, 2001 11:20 AM
To: [email-masked]'
Subject: [Megaco] H.248 equivalent of MGCP Delete from MG

Hello list, 

MGCP has the concept of a Delete from the MG to the MGC. 

So what do we do for H.248 ?  The Subtract command is intended for MGC to MG
only. 

The MG may need to use this under certain circumstances.  Examples are: 
(1) If there is detection of a packet-side bearer failure which affects a
ephemeral termination within a current context.

(2) If the MG fails to detect voice (or comfort noise) on a bearer
connection after a certain amount of time -- this may be due to a problem
with the peer MG, rather than anything wrong with the network.

(3) A temporary MG resource issue which caused it to drop the call, but
shouldn't affect future calls. 

Is there a standardised way for the MG to convey this infomation to the MGC
-- i.e. one which all MGCs will understand? 

Thanks.

---

From: "Nadathur, Srivathsan G (Srivathsan)" <[email-masked]>
Date: Tue, 14 Aug 2001 13:25:38 -0400

How about using a service change on an ephemeral termination from the 
MG to indicate "loss of connection" on the packet/ATM side.
 
Srivathsan.

-----Original Message-----
From: David Barr [mailto:[email-masked]]
Sent: Tuesday, August 14, 2001 11:20 AM
To: [email-masked]'
Subject: [Megaco] H.248 equivalent of MGCP Delete from MG

Hello list, 

Thanks. 

_______________________________________________
Megaco mailing list
[email-masked]
http://www1.ietf.org/mailman/listinfo/megaco

---

From: Matt Holdrege <[email-masked]>
Date: Tue, 14 Aug 2001 17:24:08 -0700

What happened to Service Change? This was supposed to allow the MG to 
arbitrarily ask the MGC to delete the connection.

At 08:40 AM 8/14/2001, Rosen, Brian wrote:
>The model is that the MGC is ALWAYS in control of the context.  The MG reports
>So what do we do for H.248 ?  The Subtract command is intended for MGC to 
>MG only.
>
>Is there a standardised way for the MG to convey this infomation to the 
>MGC -- i.e. one which all MGCs will understand?
>
>Thanks.

---

From: "David Barr" <[email-masked]>
Date: Wed, 15 Aug 2001 10:42:04 +0100

I'm glad you mentioned this.  What is interesting is that for the 3
scenarios below, the ServiceChange(forced) would be sent on the ephemeral,
NOT the physical termination ... because there is nothing wrong with the
physical termination.  (Note: I'm assuming a VoIP, TDM-IP call.)

Now, for a ServiceChange(forced) on a physical termination, the MG
subsequently sends a ServiceChange(restart) when the termination is
available again.  No problem.

But what about for a ServiceChange(forced) on an ephemeral termination?
Does the MG need to send a ServiceChange(restart) ?  I think the answer is
NO, because when the MGC receives the ServiceChange(forced) it SHALL
subtract the termination from the context (see ImplGuide-6.78), therefore
the ephemeral termination will no longer exist so it is irrelevant what its
serviceState is.

However, consider the following example:
(A) MGC sends an message with two Adds ... add physical (tp0) and ephemeral
($).
(B) MG successfully responds with "rtp/1234" as the ephemeral ID.  In this
example, the MG uses a standard format for ephemerals, ie. "rtp/" followed
by the UDP port number.
(C) A temporary error event occurs (e.g. scenario (3) below) which means the
MG can no longer support the call.
(D) The MG sends ServiceChange(forced) on "rtp/1234".
(E) The MGC then sends Subtract commands to tear-down the context.  The
ephemeral termination "rtp/1234" no longer exists on the MG.
(F) A few minutes later, the MGC attempts to setup a new (entirely separate)
call.
(G) It sends a command similar to (A).
(H) MG successfully responses with "rtp/1234" as the ephemeral termID.  This
is valid because "1234" is just a port number, and that ephemeral termID is
not currently being used.

Now, what will the MGC do when it receives "rtp/1234" in step(H)?  Will it
(incorrectly) think the ephemeral termination is out of service (due to
(D))?  I would say NO, because the MGC should treat this as a completely new
ephemeral termination, however this depends on how ephemerals are managed on
the MGC.  What do you think?

-----Original Message-----
From: Matt Holdrege [mailto:[email-masked]]
Sent: Wednesday, August 15, 2001 1:24 AM
To: Rosen, Brian; Barr, David [HAL02:HF22:EXCH]; [email-masked]'
Subject: RE: [Megaco] H.248 equivalent of MGCP Delete from MG

reports

---

From: "Kevin Boyle" <[email-masked]>
Date: Wed, 15 Aug 2001 10:15:27 -0400

By spec, ephemerals are destroyed upon subtract.  There should be no problem
with step H.
 
Kevin

-----Original Message----- 
From: Matt Holdrege [ mailto:[email-masked] <mailto:[email-masked]> ] 
Sent: Wednesday, August 15, 2001 1:24 AM 
To: Rosen, Brian; Barr, David [HAL02:HF22:EXCH]; [email-masked]' 
Subject: RE: [Megaco] H.248 equivalent of MGCP Delete from MG 
 
reports 
>From: David Barr [ mailto:[email-masked]
<mailto:[email-masked]> ]

---

From: "Rosen, Brian" <[email-masked]>
Date: Mon, 20 Aug 2001 13:48:05 -0400

Of course, ServiceChange is another way for the MG to notify the
MGC of errors (it would be a fatal error in most circumstances).
My bad.

The ServiceChange DOES NOT cause a Subtract; the MGC is expected
to respond to the ServiceChange with a Subtract.

Brian

> Sent: Tuesday, August 14, 2001 8:24 PM
> To: Rosen, Brian; 'David Barr'; [email-masked]'