we are using CCM 4.13 that sits behind the firewall. We are using SIP over the internet to connect to a vendor. When we make a call, our vendor can hear us but we are not able to hear our vendor. Also, call gets disconnected after about 30 sec. In the SIP header, our vendor see the IP address of the CCM (10.1.X.X) which is different than the NETed CCM ip address. Your help is greatly appreciated.