topic Re: outbound call over SIP Trunk not working but inbound calls working in Collaboration Applications

outbound call over SIP Trunk not working but inbound calls working

collinks2 — Wed, 28 Jan 2026 21:03:55 GMT

Hello everyone,

I have two sites: Site A and Site B. This is in a lab environment. both are connected via a fiber link.

Both site use cucm version 12.5

I have a sip trunk between the two CUCMS. Trunk status on CUCM B shows Full service while the trunk status on CUCM A shows no service. Both were using sip ports 5060. I changed the ports to 5065 on both cucm and the trunk status on both now show Full service.

Problem:

The endpoint on CUCM B (6571) can dial the endpoint 3005 on CUCM A.

The endpoint on CUCM A (3005) can't dial the endpoint 6571 on CUCM B.]

The sip trace using Wireshark shows call rejected. see screenshot. I don't know what is wrong

any help will be greatly appreciated

Re: outbound call over SIP Trunk not working but inbound calls working

sjdamme — Thu, 29 Jan 2026 19:39:59 GMT

It's difficult to diagnose this with just the information provided. We see the 65XX route pattern assigned to the trunk from CUCM A to CUCM B, but we don't know what the internal_css calling search space assigned to the SIP trunk on the CUCM B side provides access to. Is the partition that contains extension 6571 included in the internal_css calling search space on CUCM B? There should also be some information in the SIP packet where the call is rejected, but it's probably just Q.850 cause=21 (call rejected). You could pull SDL traces on CUCM B from the time of a failed call attempt and that should show you why CUCM is rejecting the call.

Re: outbound call over SIP Trunk not working but inbound calls working

collinks2 — Thu, 29 Jan 2026 20:04:07 GMT

Thank you so much for your contribution.On CUCM B, the internal css contains all the partitions. 6571 belongs to the internal_css and Internal_PT. On the CUCM B , the trunk that points to CUCM A has internal_css for Incoming calls..With sound 'pio pio', I was tempted to believe it's a css and partition problem. I removed all the css and partition but still no success.

Sons hours ago, I changed the outgoing transport to UDP on the Non Secure profile . After I restarted the server, 3005 was able to dial 6571. No audio and video. (Just the self video ). I dialed 3005 from 6571 :no audi and video.

There is definitely something wrong somewhere. CUCM B belongs to domain xyz while CUCMA belongs to abc. Could this contribute to the issue?.I am thinking CUCM A is the one rejecting the call because it thinks the endpoint 65xx is local .why did the call go through after changing to UDP? I changed back to TCP and the call failed

How do I pull out SDL traces on CUCM B

Re: outbound call over SIP Trunk not working but inbound calls working

sjdamme — Thu, 29 Jan 2026 20:24:01 GMT

The SIP transport being UDP or TCP shouldn't matter as long as the far end will accept it. Is there a firewall between the CUCM clusters? I have seen a SIP ALG on a firewall cause problems with TCP packets being delayed by the firewall to the point that call setup fails or is incomplete.

Based on your latest response it sounds like the call actually does ring through and connect but you just aren't getting any audio or video? Do you have all nodes from both clusters defined in the SIP trunk? In other words, if CUCM A has three nodes running the Call Manager service you need to have all three of those nodes defined as destinations in the SIP trunk to CUCM A.

Do you have a valid network path between the two endpoints? Media is endpoint to endpoint, not CUCM to CUCM (unless you have the device configured to require an MTP, but that's another discussion) so you could have a call set up correctly but if phone A can't reach phone B you aren't going to get any media.

To pull SDL traces you can follow this guide

Re: outbound call over SIP Trunk not working but inbound calls working

collinks2 — Sun, 01 Feb 2026 16:08:22 GMT

Thank you so much for your contributions. Apologies for my late response. I was trying to install the RTMT so I can get the trace. I am still finding it difficult to install RTMT on my windows 11. i have installed on more than 3 PCs but no success. I have installed java but no success. What baffles me is that I have two CUCM users . The end points in the two clusters can communicate very well over a sip trunk. Both belong to the same domain. . I don't know if it's because this cluster is in a different domain . Both clusters can resolve all their domains . There is no subscriber. Just one CUCM Publisher per cluster