Emergency Responder using two CUCM clusters

[wabrown]

We have recently setup a second 12.5 CUCM cluster that will share a CER cluster with the existing CUCM cluster. I am looking for configuration assistance for two CUCM clusters sharing the same CER cluster. I have added the second CUCM cluster under phone discovery in CER, however SNMP is failing even after verifying settings are correct (shared SNMP string name on all CUCM nodes with read only access) and restarting services. 

Beyond that, I am hoping to find out how these two CUCM clusters, which are connected via SME, can be configured to share a CER cluster and what issues I need to look out for. Do I need to create new ERLs or can I used the existing and just assign to subnets that I'll be tracking for the new CUCM cluster. I'm not sure how the CER server will know which CUCM cluster to send the call to and there does not seem to be much documentation online. I appreciate any help!

[M02@rt37 · Accepted solution]

Hello @wabrown,

Ensure that both CUCM clusters are running the same version of CER. If not, you may encounter compatibility issues.

--Configure the CER server to allow the second CUCM cluster to access it. You can do this by adding the second CUCM cluster under Phone Discovery in CER, as you mentioned. Make sure that SNMP is enabled and that the SNMP community strings are configured correctly.

--Configure the appropriate emergency response settings in each CUCM cluster. This includes configuring emergency dialing and setting up appropriate emergency call routing. You should also ensure that emergency responders have access to the appropriate location information in CER.

--Create new ERLs for the new CUCM cluster in CER. You can either create entirely new ERLs or modify existing ones to include the new CUCM cluster's subnets.

--Assign the appropriate subnets to each ERL. This will allow the CER server to know which location to send emergency calls to.

As for your issue with SNMP failing, you may want to check that the shared SNMP string is identical on all nodes in both CUCM clusters and that the correct SNMP version is being used. You may also want to check that the SNMP read-only community string is properly configured on the CER server.

[wabrown]

Thank you. That is very helpful. What if both CUCM clusters are sharing device subnets? Is there a way to configure CER/CUCM to send all 911 calls through the CUCM cluster that owns the ELIN, regardless of which CUCM the device placing the 911 call is registered to, and still provide callback functionality if the callback numbers are published between clusters via SME? Attaching diagram for clarity.

[Jonathan Schulenberg]

Small clarification: a pair of CER nodes is called a CER group. A CER cluster are multiple CER groups stitched together. This distinction is important because of one big gotcha: all CUCM clusters integrated to a given CER group must be running the same version. Unless you’re willing to upgrade both CUCM clusters in the same maintenance window you should pair them up, one CER group per CUCM cluster. Without re-reading the whole chapter on CER clusters, IIRC that design may also help with your desire for the call to be handled by the CUCM that “owns” a given ELIN from an outbound calling ANI standpoint.