S4. IMS Session Initiation signalling flow —
mobile origination in home network
termination in CS network
S4-5b. SIP UPDATE request (UE1 to UE2):
from P-CSCF1 to S-CSCF1
(21 of 48)
: The P-CSCF added the GPRS access network information to this header, which is removed and stored by the S-CSCF.