S1. IMS Session Initiation signalling flow —
mobile origination and termination roaming
with different network operators
S1-10a. SIP 200 OK response (INVITE):
from UE2 to P-CSCF2
(59 of 70)
When the called party answers UE2 sends a 200 OK final response to the INVITE request to P-CSCF2, and starts the media flow(s) for this session.