- P-CSCF1 removes any keys received in the 401 Unauthorized response and forwards the rest of the response to UE1.
- WWW-Authenticate: P-CSCF1 removes the ik and ck parameters (directives) from the header.
- Security-Server: q is the preference value, 0.1 means IPsec is the first preferred choice. The q value represents only relative degradation of all mechanisms listed here. The lower value, the higher prority.