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Call from PSTN rings but rings again on answer (transcoding issue?)

Level 1
Level 1

We have a Cisco 2911 (15.4(3)M2) that is connected to the PSTN via provider A. In preparation of switching from provider A to provider B, we have a second Ethernet interface connected to the new provider, a second SIP registration and a test DID.


Calls from the PSTN to the test DID ring on a Cisco 7961 connected to CUCM 10.5.2. However, when you answer the call, you get a momentary flash on the phone and then it goes back to as if you had not answered the call. That is, it appears that the call continues to ring. It is probably an answer, disconnect, and then a "new" call because the router has now sent the call to the publisher since the subscriber failed to handle the call.


If you answer the call again, the call disconnects (probably both CUCM publisher & subscriber have failed so we're out of options).


From the debugs, I think the "Reason: Q.850;cause=47" is the big clue but I'm not sure why. The system is idle and should have free transcoding resources available assuming that is the problem. (I believe the call is coming in as g711 from provider B.)


Calls from provider A (g729) are completing without a problem.


Pointers on where I am not looking?



2 Replies 2


The fact that a G729 call goes through and a G711 fails suggests a codec or transcoding issue.  I assume that the CUBE Region to the phone Region is set to low bandwidth in CUCM.   I suggest first check 100% on media settings, is the CUBE transcoder in the same Region as the CUBE, or in different regions then what is the bandwidth between them.  Is it included in the MRGL of the CUBE or the phone or both?

Thanks, Tony!


The bandwidth between regions (phone vs. CUBE) was the issue with getting the call to complete as G711. (Provider B does not support G729 so we couldn't negotiate down to that.)


Still have to figure out why the transcoder is not working but this a big step in at least verifying our base config works. (Regions are the same between transcoder and CUBE.)