IMS-AKA Call Establishment over TCP

For the UE to send a new request into the network and establish a call, a third TCP connection is created using the information configured/generated prior to creating the first secure connection.

1. If the TCP connection over a secure channel does not exist, the Caller will establish it.
2. The Caller initiates the call by sending SIP INVITE from its PORT-UEC to the P-CSCF's PORT-SDS.
3. The P-CSCF forwards the INVITE to the Caller. If not present, it will create a secure TCP connection from its PORT-SDC to the callee's PORT-UES.
4. The INVITE is then forwarded to the Callee securely.