R4. IMS Registration signalling flow —
P-CSCF subscription for registration state event package
R4-2. SIP 200 OK response
(4 of 10)
S-CSCF1 first authorizes the subscription. As S-CSCF1 can trust the content of the P-Asserted-Identity
header and <sip:pcscf1.visited1.net> is on the list of the authorized users for the "reg" event
package stored by S-CSCF1, therefore S-CSCF1 sends an acknowledgement towards I-CSCF1
indicating that the subscription was successful.