My configuration is as follow Cablevision as my ISP-->Cisco 831 Router/firewall -->winxp PC with 3cx PBX Software(No soft firewall). Internetcalls as sip outgoing carrier. officedigit as my incoming carrier. x-lite softphones I can send and receives a call fine. My problem is that i can not hear audio in both direction when i call from one extension behind firewall to another extension outside of firewall(Cisco 831 Router) means at remote location.I can make ext to ext call fine if they are behind the firewall. same thing is also true. if i call landline number from External ext. Any suggestion will be appreciated.I have opended all the ports which have been mentioned in the 3cx configuration guide.