Question: In the context of GIBA Security Mechanism, what is the primary purpose of the GGSN providing the user's IP address (or IPv6 prefix) and IMSI to the HSS over the Gi interface when a PDP context is activated towards the IMS system?
Option 1: To enable billing for IMS services based on IP address usage
Option 2: To facilitate NAT traversal between the GGSN and P-CSCF
Option 3: To create a secure binding between the user's SIP-level identity and bearer/network level identity
Option 4: To authenticate the UE's IPv6 stateless autoconfiguration process
Explanation: The primary purpose of providing this information is to establish a secure link between the user's identities at different levels (SIP-level and bearer/network level), ensuring that IMS signaling can be securely connected to the PS domain bearer level security context, thus preventing identity spoofing and ensuring accurate charging.