What is the problem?

3CX and Fanvil IP phone are not in the same local network, after the Fanvil phone remotely registers to 3CX IPPBX manually, Fanvil phone can dial the other 3CX extension normally. But when the other 3CX extension dials the Fanvil phone, and when Fanvil phone will ring, the other 3CX extension cannot hear any ring back tone, after the Fanvil phone picks up the call, the other 3CX extension is still dialing.

How to find the solution?

After we make one capture in the 3CX server, we can find that after 3CX sends the invite request to Fanvil phone, 3CX server does not receive any response from Fanvil phone.

After we make one capture in the Fanvil phone, we can find that when the Fanvil phone receives the invite request from 3CX server, the Fanvil phone will response to the LAN IP of 3CX, not public IP of 3CX.

 

It is because after the Fanvil phone receives the invite request, at default Fanvil phone will response to the address of Via in the invite request, and in the invite message, we can find that the address of Via is the LAN IP of 3CX, so that 3CX server cannot receive any response from Fanvil phone.

What is the solution?

Please login the web page of Fanvil phone, and go to Line->SIP->Advanced Settings, enable the option: Enable Strict Proxy, then the Fanvil phone will response to the address of contact in the invite request, not the address of Via. After that, the Fanvil phone and the 3CX extension can call each other normally now.

 

For Fanvil ip phone, please check

 

https://en.58voip.com/product/fanvil-x7/