No sound on outgoing calls

Hi every one, I am new in freepbx and I installed the freepbx and configured my extensions but I have a problem that sound is working between my extensions but on out calls sounds not working at all. my freepbx IP Address is my gateway is the sip provider IP is I am connected to sip provider directly via SDH switch there is no router and firewall between. please guide.

Routing problem. If the call is setting up, but there is no audio, the RTP packets are dropping somewhere. What is your RTP range (default is 10000-20000)? Run a Wireshark to see where the traffic drops.