Subject: [Megaco] active terminations behaviour when MGC switchover

From: "Ron Ho" <[email-masked]>
Date: Thu, 18 May 2006 19:38:15 -0400

Hi All,

Can anyone show me what the active termination behaviour should be
when MGC decided to switch to a standby MGC with
SC(Handoff/903/mgcid)? Should the current MGC tear down all the active
terminations first? Or, would the MG maintain the current state of all
terminations just switch the MGC control over assuming the new MGC
know everything about it existing connection? Should the standby MGC
mirror all the current MGC state regarding all terminations? Should
the standby MGC audit the MG once it took over the control?

Thanks,
Ron

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From: [email-masked]
Date: Fri, 19 May 2006 11:03:46 +0200

Ron,

I've copied below the relevant part of H.248.1, my interpretation is that
this question was intentionally not addressed in detail in H.248 ("...
HandOff maintain state information; this is considered to be out of scope
..."), because there is principally a wide range with regards to
"service/network availability" targets (-> "stable call preservation",
"stable bearer preservation") and correspondent performance metrics. The
aimed/requested availability figure is primarily implementation specific,
but doesn't change below H.248.1 sections.

I do agree that high service availability could only be achieved by MGC&MG
both, hence you've to specify the behaviour of your raised questions
somewhere (note: ETSI work item 03051 could be a potential place for that,
or H.248 profiles could provide that level of detail).

- Albrecht

H.248.1 Version 3:

§ 11.5 Failure of an MGC
...

No recommendation is made on how the MGCs involved in the HandOff maintain
state information; this is considered to be out of scope of this
Recommendation. ...

§ F.3.11  MGC Redundant Failover

When the MGC in a control association encounters a maintenance or failure
condition such that it must go OutOfService, it may direct the MG to a
specific secondary MGC by sending a ServiceChange command with a
ServiceChangeMethod of "Handoff", a ServiceChangeReason of 903 ("MGC
Directed Change") and the address of the new MGC in the ServiceChangeMgcID
parameter.  The control association is terminated upon the receipt of the
command reply from the MG. The MG then sends a ServiceChange Command to the
specified MGC with a ServiceChangeMethod of "Handoff" and a
ServiceChangeReason of 903 ("MGC Directed Change"). A new control
association is established upon receipt of the command reply from the MGC.

In the event that the specified MGC rejects the handoff attempt or the MGC
is unable to send a ServiceChange Command with ServiceChangeMethod Handoff
due to failure, the MG shall revert to the procedures for lost
communication outlined in clause F.3.6, starting with its provisioned
primary.

...

F.4.1.1   ServiceChange Method Behavior on the Root Termination
...
5.    Handoff ? When sent by the MGC, the MGC indicates that the MG is
being transferred to a new MGC. This terminates the current control
association, upon receipt of the command reply. When sent from the MG to
the MGC, this indicates that the MG is attempting to establish a new
control association in accordance with a handoff command received from the
MGC in its previous control association. When sent from the MG to the MGC,
a handoff is a registration, and a new control association is established
upon receipt of the command reply. The MG shall not use Handoff without
being commanded to do so by an MGC.

                      "Ron Ho"                                                                                                     
                      <ron.ho.megaco@g         To:      megaco <[email-masked]>                                                   
                      mail.com>                cc:                                                                                 
                                               Subject: [Megaco] active terminations behaviour when MGC switchover                 
                      19.05.2006 01:38                                                                                             

Hi All,

Thanks,
Ron