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.

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