S1. IMS Session Initiation signalling flow —
mobile origination and termination roaming
with different network operators
S1-1e. SIP INVITE request (UE1 to UE2):
from S-CSCF2 to P-CSCF2
(6 of 70)
S-CSCF2 remembers (from the registration procedure) the UE Contact address and the next hop CSCF for this UE.
: Built from the Path header stored at registration.
: S-CSCF2 adds itself.
: Includes the dialled URL with its parameters.