Remote Extension No audio/UNREACHABLE

Hi Team,

I have installed freePBX which comes in iso format within CentOS. I have static IP —> Firewall/Router—>PBX server architecture in my office. All sip extension are working fine with PSTN as well as extension to extension in local LAN.But when I am registering extension (remote extension) out of my network with static IP (Forwarded port UDP 5060, 10000-20000 in my router), it gets register successfully, but when i am checking the seep peers this remote extension shows status as “UNREACHABLE”. and not getting audio from onside and sometimes on both sides.

Please suggest any extra configuration which suppose to make to troubleshoot the issues.