The software can be used by interviewers who do not have fixed IP addresses and who work behind a NAT. TCP/IP and UDP protocols will be used for handling calls and to voice data transmission. By default Softphone listens on the 5060 port (or higher, if the 5060 port is already used). A voice call is setup on a high UDP port, determined by the CallServer. By default, connection with the CallServer uses the 5060 port and a higher one, negotiated during the call setup process. In case of Proxy connections, the connection from the CallServer is initiated on the fixed port 5080 by default.