S2. IMS Session Initiation signalling flow —
mobile origination and termination in home network
S2-8a. SIP PRACK request (UE1 to UE2):
from UE1 to P-CSCF1
(47 of 70)
: Takes the value of the Contact header of the received 180 Ringing response.
: Contains the security agreement as represented by the received Security-Server header.