S2. IMS Session Initiation signalling flow —
mobile origination and termination in home network
S2-1. SIP INVITE request (UE1 to UE2)
(1 of 70)
UE1 is located in the home network, and determines the P-CSCF via the CSCF discovery procedure.
P-CSCF1 knows the name/address of the S-CSCF from a prior Registration performed by UE1.