IAX2 extensions no ringback on sip trunk - Asterisk 13


I know it is not new but I am still looking for a solution for it. People said something about ringing() but people do not even mention how to do it on the Internet.
My problem just like others. When a phone registered using IAX2 protocol, there is no ringback but it still connects to third parties. Until the third parties say “hello”, extension users can communicate with each other.