No outbound audio on a few specific inbound calls only

Hi: I’ve searched / researched this issue prior to posting - so far, I’ve not come to a solution.

We have a FreePBX (recently upgraded to FreePBX on-site. It generally works great, handling calls inbound/outbound from thousands of phone #s. In the last 6-12 months I’ve received several reports of audio problems with inbound phone calls from certain customers.

For these callers, the issue is always the same:
When they call us, we can hear them but they cannot hear us (we’ve tried placing them on hold - they also cannot hear the hold music). If we hang up and call them back, the connection works fine, with inbound and outbound audio working perfectly. This behavior is always consistent; those inbound calls with have the audio issue every single time, and calling them back always has no issues.

Other inbound calls also continue to work consistently with no audio or other issues.

Our FreePBX server is NAT’d via our router/gateway; the router is configured to forward UDP ports 10000-20000 to the LAN IP of our FreePBX server.

We are located in the United States (NY) and the problem calls are from local numbers; other calls from the same area code work without any issues.

While the “workaround” of calling these customers back has allowed us to continue to do business, there is increasing pressure to resolve this issue. Thanks for any help in resolving this; I can post further details and or call logs as needed.

Who is the carrier for your problematic DID(s)? Who is the carrier for the failing callers? (Look these up at, unless you have access to better tools.)

If you have DIDs on different carriers (for example a local number and a toll-free number), do you have the problem on calls to both numbers?

A log with a SIP trace would be useful. At the Asterisk command prompt, type
pjsip set logger on
sip set debug on
according to your incoming trunk type. Ask the customer to call in, paste the Asterisk log for the call at and post the link here.

Thank you Stewart1 - you pointed me in the right direction to resolve this as well as gave me some good ideas to consider / remember going forward.
The problem #'s were all carried by Verizon. When I had one of them try calling us via a DID with our backup SIP provider, there were no issues.
When I discussed with Flowroute, (our primary SIP service) they informed me that they’ve had some issues with Verizon and audio in the past. They changed the “peer” for our primary DID and after that, the issue appears to be resolved.
Naturally I’m disappointed that I won’t have the need to gather and post detailed SIP logs, but maybe next time (/S).
Thanks again for your help in getting this resolved. Much appreciated.

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