CUCM failed over with DTMF

[fedor.solovev]

Hi everybody.

I have schema with 2 CUCMs connected via SIP trunk. Users may dial with XXX numbers between these CUCMs. However, if SIP trunk failed I need to make seemless failover calls between CUCM1 User A and CUCM2 user B. But this failover should be with DTMF, therefore something should generate this DTMF on the one site, and something should accept DTMF and route call to an internal extension at the other site.

I realise that the easiest way is to have direct PSTN numbers without any DTMF, or

it is possible to use UCCX in some ways. May be Cisco IOS GW could do this ?

[Chris Deren]

Hmm, when you say you have 2 CUCMs do you mean 2 clusters or 2 servers in a cluster?

I dont follow your issue, can you describe the call flow in more details?

[fedor.solovev]

Hi, Chris.
thank you for asking.
Schema looks like Phone1->CUCM1 -> SIP Trunk -> CUCM2 ->Phone2
during SIP Trunk failure CUCM (or other GW) should transfer calls via PSTN (or ITSP) in order to reach Phone2 (and vice versa).
Since Phone1 and Phone2 has XXX format numbers, something should generate DTMF during SIP Trunk Fail Over when CUCM sends a call via a provider.
Speaking about what can accent DTMF, I guess this could be UCCX, Unity or a script on IOS router.
The first quetion is how to send DTMF during failover.

[Chris Deren]

First of all I am assuming each cluster has more than a single CUCM server in it, so your SIP trunk between the clusters should reference all CUCM call processing subs for maximum redundancy.

Then for PSTN failover in the Route List that points to the RG-->SIP Trunk, add secondary Route Group that is "Standard Local Route Group" (assuming you use SLRG, otherwise you are limited to hard coding specific site's RG) and prepand proper digits to expend the number to full PSTN number (i.e. 91XXXXXXXXXX), this obviously will only scale if your dial plan can accomadate it. 

I still dont follow the DTMF question as I dont see how if fits into this.

[fedor.solovev]

Hi,

thank you for you answer.

I am considering WAN failover that is why amount of CallManager services within a cluster doesn't play a role.

The point is that subscribers don't have their own PSTN numbers. Both of clusters has something like Unity or UCCX in order to acept DTMF to transfer calls to internal (3-digit numbers) subscribers.

That is why something should send DTMF via PSTN during failover.

[fedor.solovev · Accepted solution]

Chris,

thank you. I opened a case in order to confirm that this wouldn't work.
They confirm that during WAN (SIP/H.323 Trunk) failover between two clusters my desired schema wouldn't work.