https://community.cisco.com/t5/collaboration-applications/connectivity/m-p/3768188#M38522 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.<BR /><A href="https://www.netcraftsmen.com/sip-endpoints-in-cisco-cucm-x-lite-as-an-example/" target="_blank">https://www.netcraftsmen.com/sip-endpoints-in-cisco-cucm-x-lite-as-an-example/</A> Sat, 22 Dec 2018 12:55:47 GMT Jonathan Schulenberg 2018-12-22T12:55:47Z https://community.cisco.com/t5/collaboration-applications/connectivity/m-p/3764794#M38479 <P>i have one Existing Avaya PBX&nbsp; 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.</P><P>&nbsp;</P><P>Customer need the above solution could you explain me if any one face above issue&nbsp;&nbsp;</P> Mon, 17 Dec 2018 06:48:54 GMT https://community.cisco.com/t5/collaboration-applications/connectivity/m-p/3764794#M38479 immu_91700 2018-12-17T06:48:54Z https://community.cisco.com/t5/collaboration-applications/connectivity/m-p/3768188#M38522 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.<BR /><A href="https://www.netcraftsmen.com/sip-endpoints-in-cisco-cucm-x-lite-as-an-example/" target="_blank">https://www.netcraftsmen.com/sip-endpoints-in-cisco-cucm-x-lite-as-an-example/</A> Sat, 22 Dec 2018 12:55:47 GMT https://community.cisco.com/t5/collaboration-applications/connectivity/m-p/3768188#M38522 Jonathan Schulenberg 2018-12-22T12:55:47Z