If my users use 3CX softphone or Grandstream phone at home, they can cannot heard people talking but people can heard them no problem. I uses 3CX softphone debug feature and it shows OK no problem. I also put STUN server stun.3cx.com on 3CX softphone and Grandstream phone and it is still one way audio. What else can I try it? p.s. if the home PC uses VPN connection to 3CX phone server, there is no one way audio problem on 3CX softphone. Really thank you for your helping.