From Trunk1 to Trunk2 call



I have:
FreePBX behind NAT
Trunk1 to service provider A
Trunk2 to service provider B
Multiple internal extensions

calls from/to Trunk1 works fine.
calls from/to Trunk2 works fine.

Now I change Incoming Route for Trunk1, and set destination to “Misc Destinations”, and set destination dial = mobile number.
Outbound route for this number = via Trunk2.
But now called party see call, but both callers cannot hear each other.

How to fix it?

PBX Firmware:6.12.65-32
Asterisk (Ver. 11.25.3)


Confirm that your router/firewall is forwarding all RTP ports to the PBX. Default is UDP 10000-20000.

If that’s not it, post details of your network.


VM with FreePBX have full unrestricted access to internet via stateful firewall.


Confirm that if the trunk sends a UDP packet to the public IP e.g. port 12345, it will reach the PBX, even though the PBX hasn’t yet sent one from that port.


I already wrote:

  1. calls from/to Trunk1 works fine.
  2. calls from/to Trunk2 works fine.
    This is not enough?


Yes, it’s not enough. On a call to Trunk1 answered by (for example) an extension, audio sent by the extension is relayed to the trunk, so audio sent by the trunk appears as ‘replies’ and is passed by the firewall. But on a trunk-to-trunk call, no audio is sent until some is received, but nothing is received because the firewall blocks it until something is sent.

If the firewall is not within your administrative control, you can work around the problem by routing the call to an Announcement, e.g. 1/2 second of silence, and then to the Misc destination. Many other workarounds are possible, but the recommended solution is to forward the RTP port range to the PBX.

(Greg Snover) #7

My guess would be that you are trying to pass foreign Caller-ID out through a trunk that doesn’t like it - This will often result in a reject of the call - Simple way to test - go into your outbound routes and force the caller-id on the trunk you are trying to outbound on to the trunk caller-id and re-test.

If that is the case, your trunk provider is kind of lame.


Not related to this problem:

(Greg Snover) #9

Sorry - not reading closely enough.

(Lorne Gaetz) #10

If you answer the call and play a recording before forwarding to the outbound number, does the audio work then? If so, the issue is probably as @Stewart1 said in post 1, firewall is blocking inbound RTP.


I just set destination to “Queues”, and add mobile number to Static Agents.
Now everything works fine!

(system) closed #12

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