CUCM 12.5 fails to send an ACK to CUBE

[MityoValchev32163]

Hello,

Occasionally I have outbound calls which fail due to lack of ACK from CUCM on a 200 OK from CUBE. The flow goes as shown in the diagram below. Normally a network issue is causing such problems. Here however there is nothing between the CUCM and the CUBE. I am about to open a case with TAC, any suggestions prior that are welcome.

[b.winter]

How does the flow look like in perspective of the CUCM?
Does CUCM ever get an ACK from the calling device?

[MityoValchev32163]

No, the calling device does not send an ACK. The calling device is not a physical phone or a softphone. It is a CTI port, more specifically an RCP port. We have this setup to allow work from home (incoming on a Service Line----->UCCE---->CUCM (LCP port)------->CUCM (RCP Port)------>Agent's mobile phone.

[TechLvr]

Could you upload the actual sip logs as a text file? You can sensor all the sensitive data before uploading. 

[MityoValchev32163]

These are the logs from CUBE

[MrButton]

what do you have setup for the SIP profile under the trunk?  

I had to do Send PRACK and early offers on SDP because I would get similar situations like yours.

Here is what I have in one of the sip trunks.  

[MityoValchev32163]

My SIP trunk config is the same

[MrButton]

what type of connection do you have after the dial-peer connects to the PSTN? Is the handoff a SIP?  SIP Cloud? I implemented a SIP Cloud a while back at another place I was at, because it was cheap.  This went off via internet over a firewall.  At the time this was an ASA5515.  I'd sometimes get ACK sometime wouldn't, or I would just get a call drop after 10 minutes.  I had to disable some default policies for port 5060.  Once I fixed that issue that location never had an issue with voice.

Your case may be different than the ones I have encountered.

Have you engaged with your service provider to see what their system is showing up on their logs? 

[MityoValchev32163]

My missing ACK is between CUBE and CUCM, that is all internal. Provider does not have much to do here. Apart from that the outgoing call flow will be: Endpoint---->CUCM---->CUBE---->CUSP----SIP Provider. After CUSP all is a black box to me.