Question: What is a primary concern if a malicious UE bypasses the P-CSCF and sends SIP messages directly to the S-CSCF in an IMS network?
Option 1: The UE may experience reduced QoS (Quality of Service) for its SIP sessions.
Option 2: The network may not be able to generate accurate charging information for the UE's activities.
Option 3: The UE will automatically be blocked from accessing any IMS services due to built-in security protocols.
Option 4: The S-CSCF will always reject SIP messages not coming through a P-CSCF, preventing any potential issue.
Explanation: Bypassing the P-CSCF allows a malicious UE to evade the integrity protection provided by IPsec ESP between the UE and the P-CSCF. One of the significant problems this presents is that the P-CSCF cannot generate charging information for the UE's IMS activities since it is not aware of them, directly impacting billing and revenue assurance for the network operator. This highlights a critical security and operational concern rather than just a QoS or simple protocol rejection issue.