[Serusers] Can't make a single call. Help me please.

Hi allAfter spending whole week reading and googling I am writing here. Hope someone from here can help me.Here is my setup -I have a Fedora 7 desktop with SER, mysql, and rtpproxy running. This is connected directly to the cable modem. There is not NAT in between. Firewall and SELinux are disabled.I have X-Lite client on my Laptop connected to a Wi-Fi router on a different IP. This router has NAT but the firewall is disabled in the router.On the far end, my sister has X-Lite on her desktop which is also behind NAT.Both X-Lite clients can REGISTER and the SIP server sends 200 OK. But can't make calls.When all clients and SER are on the same network with local IP addresses, I can make calls between the X-Lite clients and SJPhone on different computers. No problem. And Grandstream phones also work in the local setup.Any help is appreciated.HS