Branch router, call manager, PRI and call flow

Unanswered Question
Jun 10th, 2009

We have several sites connected via MPLS.

We have call Manager in the main site and the branches perform branch to branch calling via the MPLS link.

Each branch has a PRI for local (to the branch) calling.

The routers are configured for SRST if call manager is lost.

My understanding is that this command will ensure the router will use call manager to process calls rather than the local gateway:

"isdn bind-l3 ccm-manager", if the gateway can reach call manager.

When the branch is making a local call, out the branch PRI, does the local handset use Call Manager for this?

For example, the communication would be:

1. Handset picked up

2. local gateway passes to call manager

3. call manager tells phone to use local PRI

I have this problem too.
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parshah Wed, 06/10/2009 - 10:52

Hi,

Your assumption is correct. Basically there are 2 things you need to keep in mind. The IP Phones and MGCP gateway communicate with CUCM seperately.

As long as there is connectivity between the CUCM and phones and gateway everything is controlled by CUCM. So when an IP Phone goes off hook and dials out to PSTN, the call routing, digit manipulation is done by CUCM and call is sent out local gateway to PSTN if its configured properly.

Now, if connectivity is lost between the HQ and branch office, since you have SRST configured, the phones will register with local GW. In this case the local gateway becomes a CME and call routing, digit manipulation will be done by the local gateway.

Thanks,

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