Subject: [Megaco] MGC-MG dialogue failure detection

From: [email-masked]
Date: Fri, 5 Jul 2002 09:57:20 +0200

I would like to point out an issue which is as far as I know is not solved
in RFC3015.

I suppose that the  MG is registered to the MGC and that there is no
transaction on going.
If the MGC fails, there is no way for the MG to detect it when using UDP.

I have already seen two mechanisms implemented by stack vendors to solve
this issue :

1- Use of ping to detect that the correspondent is no more reachable
2- Use of a ServiceChange ROOT with termination = undefined as a  polling
mechanism

     * on MGC side if no response to the poll, return to initial state
waiting for a ServiceChange
        from the MG. Inform the Call Control that  the terminations are no
more usable
        to establish new calls

     * on MG side if no response to the poll, return to initial state and
try to retrieve the dialog
        by sending ServiceChange to the primary MGC  or to the secondary
MGC if it is provisioned.

I think that to avoid that everyone defines it own mechanism which can lead
to interoperabilty problems
it should be defined in the RFC.

Jean-Luc Lecuyer
--------------------------------------------------------------------------------------------
Jean-Luc Lecuyer :          VND/E10 VS  BU R&D/CCPD Lannion
Full telephone number :                                         33 (0)2 96 04 77 09
Full fax number :                                                        33 (0)2 96 04 72 35
Email :                                                         [email-masked]
---------------------------------------------------------------------------------------------

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

---

From: "Rajeev K R" <[email-masked]>
Date: Sat, 6 Jul 2002 09:17:32 +0800

Hi Jean-Luc,

ITU-T SG16 has published a document named
H.248 Annex M.6: Inactivity Timer Package
which can be used by MG to detect the MGC failure.
MG can send Notify with event=it/ito and chcek whether MGC gives a response.
When there is no response for some number of attempts, MG can initiate
registration procedure.

From the MGC side the package suggest the use of Audit for ROOT with empty
descriptor.

But there is another problem, the standard still does not address. This is
more from a practicality
point of view. This is from the MGC side. Suppose the MGC detect that the MG
is not responding and
mark that this MG is unregistered.
Now how can the MGC inform the MG that its registration is removed ?
If the MG is actually down there is no problem because when the MG comes up
again, it will register.
If the MG is not down, it will never register again.
When it tries to initiate a call, it will get a response that the MG is not
registered.
Some MGs register again when they get this response, but some MGs do not.

Another scenario is where all the MGs are registered, but the MGC go down
and come up.
How can the MGC force the MGs to register again ?
Is the MGC allowed to use the previous state of registation(state before it
went down) for its MGs ?

Regards,
Rajeev

---

From: "Rajeev K R" <[email-masked]>
Date: Sat, 6 Jul 2002 09:17:32 +0800

Hi Jean-Luc,

Regards,
Rajeev