Outbound calling issues (intermittent)

[scampbell_adnet]

We seem to be having issues with intermittent one-way audio on outbound calls. The caller can hear the callee, but not vice versa. Reportedly, when callees call right back, audio works just fine.

This issue cropped up at the beginning of last week, and the only constant seems to be when calling the people using cell provider Tmobile. I know there were issues with Tmobile reported last Monday, but this seems to be dragging on.

It's a difficult problem to recreate and happens randomly, some calls work, some calls don't. I'm starting to think it may be something on my 3cx server config or a Flowroute issue. We have many FreePBX systems behind the same firewall and have had no issues like this reported. The issue has happened on both v16 and v18 servers. Firewall checks pass on all affected systems. I'm at a bit of a loss with what could be causing the problem,

Any advice would be appreciated.

 

[cobaltit]

I'd start with opening a ticket with Flowroute and have them investigate.

 

[ChrisC_3CX]

The caller can hear the callee, but not vice versa.

You could first reach out to the SIP Provider as @cobaltit suggested, but, if this is only affecting outbound calls and the issue is always that the callee cannot hear the caller(the caller being the 3CX user) then you could at least confirm if it's a problem on your end or not by performing a packet capture and analyzing the outgoing RTP stream. If you can see it leaving your 3CX PBX and headed towards your provider then it's very likely that it's nothing on your end unless of course it has something to do with your firewall.

You can find a bit more information on how to analyze the RTP stream using wireshark in our troubleshooting course here: https://www.3cx.com/3cxacademy/videos/advanced/basic-troubleshooting/

If you do confirm this to be the case (media traffic IS sent to the SIP Provider) then you'll be able to contact them with a bit more proof to get things moving.

 

[scampbell_adnet]

Thanks for the suggestions. I have a ticket open with Flowroute, just wanted to check in to see if there were any other possibilities. The issue seems to be rather inconsistent, so getting a packet capture has proved to be difficult.

I can however see the calls in the CDR reports in our Flowroute portal login, so I know they're at least hitting them. We have no ports being blocked or forwarded on the firewall, and other platforms/SIP providers work just fine on the same firewall. I will continue to provide examples to Flowroute and see where that goes.