Hello, since a month or so some calls to external cell phone numbers have that problem that the other party cannot hear us, but we can hear them. That seems to happen only to some numbers, for example I cannot reproduce that calling my verizon/xfinity phone, but when calling my colleague with phone in Tmobile, it happens randomly, every second or third call.
I have captured and reviewed pcap on calls that have that problem, and calls that dont and wasnt rly sure what I am looking for. Interesting finding was on the router, checking data flow connections. It shows that when the call is good on both sides, there is just one RTP connection with external media server made, it is always server of ip similar to 206.147.84.120, connecting to our freepbx server on some port between 10000-20000. However, when the call has the problem, and receiving end cant hear us, there are 2 RTP flows with a media server, from which one tries connect to our freepbx on port like between 20000-60000. Our freepbx is configured with default ports 10000-20000. That looks like it tries to open separate RTP flows for incoming and outgoing data? I havent tried to edit RTP Port Ranges in the freepbx settings yet.
this is a single flow when call is all right and both parties can hear each other. Port 13456
this is when receiving party cant hear anything. There are 2 flows, from which one with port 52727
Again, this issue happens only when it is outgoing call, only to external number, and as mentioned, not all numbers