MGCP call preservation of PRI (no fallback)

Answered Question
Sep 30th, 2010
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Hello all,


I have a voice gateway 3845 hosting a PRI on it, backhauled to a CUCM cluster using MGCP.

There is no SRST feature enabled on the gateway nor H323 configuration (no fallback mode).


Because I want to be sure to not receive incoming calls from telco when the backhauling is lost, I added the command:

ccm-manager shut-backhaul-interfaces

This command forces the shutdown of the ISDN layer2 when the MGCP connection is lost with a CUCM.


I would like to know which behavior will occur in this scenario:


1- outgoing call active from an IPPhone through the gateway and PRI

2- first CUCM connection is lost (CUCM down) --> GW fails over to second MGCP host

3- second CUCM's MGCP connection becomes active


What about call preservation in this case? Does my call remain active during this failover? Even with the "shut-backhaul-interfaces" command?


4- first CUCM becomes active, gateway registers to CUCM back --> switchover


Call preservation?


In fact, I am pretty sure the connection would remain active without the command "shut-backhaul-interfaces". Normally, MGCP call preservation is supported with PRI when there is no fallback configured on the router.

My question is: which impact the command "shut backhaul" to this?


Thank you for your help.

Best regards,


Yorick

Correct Answer by Felipe Garrido about 6 years 8 months ago

AFAIK, MGCP call preservation will only work when the gateway failovers to another CUCM node. It does not work when failing over to SRST. That command, ccm-manager shut-backhaul-interfaces, will disable the circuit on the interface level. Any call on that PRI will get dropped when layer 2 goes down.  That should not happen when failing over between CUCMs, only when there are no CUCMs to failover and the bakhaul socket is torn down.


-Felipe

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Correct Answer
Felipe Garrido Thu, 09/30/2010 - 07:46
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  • Cisco Employee,

AFAIK, MGCP call preservation will only work when the gateway failovers to another CUCM node. It does not work when failing over to SRST. That command, ccm-manager shut-backhaul-interfaces, will disable the circuit on the interface level. Any call on that PRI will get dropped when layer 2 goes down.  That should not happen when failing over between CUCMs, only when there are no CUCMs to failover and the bakhaul socket is torn down.


-Felipe

Yorick Petey Thu, 09/30/2010 - 13:46
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Hi Felipe,


And the answer is... you were right!


I made a DRP test tonight with my customer in order to validate the infrastructure.


I confirm, when there is no SRST configured on the voice gateway (essential condition), the backhauled interfaces preserve the active calls as far as there is still one CUCM node reachable.

Even with the "shut-backhauled" command, the MGCP agent fails over correctly to the second and third CUCM node, and maintain the calls active.

Only when the last CUCM node is shut, the layer 2 of the interface is shut too by the gateway.

This was very good and worked as expected.


Thanks a lot for your opinion which turned me confident with the test before applying it with the customer, I was not so sure of the result.


Yorick

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