Connectivity

[immu_91700]

i have one Existing Avaya PBX  and new Cisco Network i have to ask you if the Avaya PBX goes down how Avaya Phone will come and register with Cisco CUCM is there any solution for this Topology.

Customer need the above solution could you explain me if any one face above issue  

[Jonathan Schulenberg]

If you can configure the Avaya phone to register to a third-party SIP Registrar/Proxy it may be possible, though likely with limited functionality. CUCM supports generic 3rd-party SIP phones.
https://www.netcraftsmen.com/sip-endpoints-in-cisco-cucm-x-lite-as-an-example/