S3. IMS Session Initiation signalling flow —
origination in CS Network
mobile termination in home network
S3-1b. SIP INVITE request (UE1 to UE2):
from I-CSCF1 to S-CSCF2
(3 of 48)
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.