S5. IMS Session Initiation signalling flow —
mobile origination and termination in home network
terminating UE roaming and busy
S5-1. SIP INVITE request (UE1 to UE2)
(1 of 14)
The UE is located in the home network, and determines the P-CSCF via the CSCF discovery procedure.
The P-CSCF knows the name/address of the S-CSCF from a prior Registration performed by the UE.