S5. IMS Session Initiation signalling flow —
mobile origination and termination in home network
terminating UE roaming and busy
S5-1d. SIP INVITE request (UE1 to UE2):
from I-CSCF2 to S-CSCF2
(5 of 14)
The I-CSCF does not add itself to the Record-Route header, as it has no need to remain in the signalling path once the session is established.