S1. IMS Session Initiation signalling flow —
mobile origination and termination roaming
with different network operators
S1-5c. SIP UPDATE request (UE1 to UE2):
from S-CSCF1 to S-CSCF2
(30 of 70)
: S-CSCF1 removes the GPRS access network information to this header and stores it.