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Walkthrough Wednesdays

ICT Call - Conference Issue



Scenario: CUCM Cluster A, CUCM Cluster B and a CUBE added as SIP Trunk on the Cluster B;


When a call is made from an IP Phone from the cluster A (via ICT to cluster B),  to the PSTN via SIP Trunk on the Cluster B, after the call is established, if the phone on the Cluster A presses the conference key, the call is dropped:


If the call is just between both clusters, the conference works without any problem.


Any idea?



Suresh Subramanian
Rising star

do you have the Conference Bridge available in the MRGL assigned in the ICT of Cluster A?

if ClusterA to ClusterB is negotiating G729 codecs, then you would need Hardware Conference Bridge in the MRGL.

//Suresh Please rate all the useful posts.

Hi Suresh,


But since the Phone A has a conference bridge on its MRGL, shouldn't it be enough? And also, the internal conference calls via cluster work.


Thanks. Regards

yes we have g729 hardware conference bridges capable.

Robert Shaw


What is the outcome if an IP Phone on Cluster B makes a PSTN call on the SIP Trunk connected to Cluster B and presses the Conference button?  I take it this works, but it's not clear.

Also, what are the configured Codecs between each leg of the call? Cluster A to Cluster B and Cluster B to CUBE.



Yes. It works locally: phone on cluster B to PSTN via Sip Trunk on cluster B. What does not work is if the call is started on a phone on cluster A via ICT to PSTN, via Cluster B. But a conferecence call between Cluster A and B also works.


G729 in all the call flow and cfb bridge hardware resources.

If memory serves me correct I'm pretty sure Conference Bridges are G711 only.  They always used to be anyway.  If this is the case you will also need transcoding resources available on Cluster A.  If possible, the best way of confirming would be to change the codec to G711 at each leg of call flow temporarily and test.

Software conference bridge will not support G729 codecs, so as I said earlier, please create hardware CFB if you don't have it already. 


Also Check the below threads pls which will give you more insight.

//Suresh Please rate all the useful posts.
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