IMS Registration signalling flow —
User not registered
R1-3a. SIP REGISTER request, with credentials: from UE1 to P-CSCF1(13 of 22)
This carries the response to the authentication challenge received in step 11 along with the
private user identity, the realm, the nonce, the URI and the algorithm.
This message is protected by the IPsec SA negotiated.
Contains the security agreement as represented by the received Security-Server header.