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Unable to Call Between Clusters – Intercluster Trunk Setup Issue

William Pacheco
Level 1
Level 1

Hi everyone,

I’ve recently configured an Intercluster SIP Trunk between two CUCM clusters (Cluster A and Cluster B).
The SIP Trunk shows as "Active", but when I try to dial from a phone in Cluster A to a phone in Cluster B,
the call fails with a fast busy tone.

Any help would be appreciated

1 Accepted Solution

Accepted Solutions

Hi @William Pacheco 
i suggest to do this checklist:

1- Make sure the CSS assigned to the SIP Trunk in Cluster A includes the Partition of the phones (or translation patterns) in Cluster B


2- Make sure the number dialed from Cluster A matches the expected dial plan format in Cluster B

3- Double-check the following on the SIP Trunk:

Destination Address is the IP address or FQDN of the remote CUCM node (preferably Publisher or SIP-Enabled Subscriber).

Media Termination Point Required: Try enabling it for testing.

Security Profile: Ensure both ends use compatible non-TLS or TLS settings.


4- Double-check Route Pattern points to the correct SIP Trunk,
& There’s no overlapping pattern that could cause a routing conflict

5- Use Real-Time Monitoring Tool (RTMT) to trace the call & Look for any call routing rejections or digit manipulation issues.

(Rate by "Helpful" or "Accept") (محمدرضا هادی_ایران) (Email: morez.hadi@gmail.com)

View solution in original post

4 Replies 4

Hi @William Pacheco 
i suggest to do this checklist:

1- Make sure the CSS assigned to the SIP Trunk in Cluster A includes the Partition of the phones (or translation patterns) in Cluster B


2- Make sure the number dialed from Cluster A matches the expected dial plan format in Cluster B

3- Double-check the following on the SIP Trunk:

Destination Address is the IP address or FQDN of the remote CUCM node (preferably Publisher or SIP-Enabled Subscriber).

Media Termination Point Required: Try enabling it for testing.

Security Profile: Ensure both ends use compatible non-TLS or TLS settings.


4- Double-check Route Pattern points to the correct SIP Trunk,
& There’s no overlapping pattern that could cause a routing conflict

5- Use Real-Time Monitoring Tool (RTMT) to trace the call & Look for any call routing rejections or digit manipulation issues.

(Rate by "Helpful" or "Accept") (محمدرضا هادی_ایران) (Email: morez.hadi@gmail.com)

thanks @Mohammadreza Hadi 

i checked CSS on both inter cluster trunk between two CUCM, and fix my problem..
issue was from wrong CSS selected..

You don’t mention if you have created any call routing configuration to make calls between your clusters. A inter cluster trunk in it self does not enable call routing between your clusters, you’d need route patterns for that.



Response Signature


thanks @Roger Kallberg for your attention

yes, i created router pattern between them,
but problem was from wrong CSS selected in trunk between two CUCM