S1. IMS Session Initiation signalling flow —
mobile origination and termination roaming
with different network operators
S1-3b. SIP PRACK request (UE1 to UE2):
from P-CSCF1 to S-CSCF1
(17 of 70)
P-CSCF1 removes the Security-Verify header and associated "sec-agree" option-tags prior to forwarding the request. As the Proxy-Require header is empty, it removes this header completely.