S1. IMS Session Initiation signalling flow —
mobile origination and termination roaming
with different network operators
S1-5b. SIP UPDATE request (UE1 to UE2):
from P-CSCF1 to S-CSCF1
(29 of 70)
P-CSCF1 removes the Security-Verify header and associated "sec-agree" option-tags prior to forwarding the request. As the Require and Proxy-Require headers are empty, it removes these headers completely.
: P-CSCF1 adds the GPRS access network information to this header.