IMS Registration signalling flow —
User not registered
R1-2c. SIP 401 Unauthorized response: from P-CSCF1 to UE1(11 of 22)
P-CSCF1 removes any keys received in the 401 Unauthorized response and forwards the rest of the
response to UE1.
P-CSCF1 removes the ik and ck parameters (directives) from the header.
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