Question: In a 3GPP network, when Lawful Interception (LI) is activated for a target with an already established IMS media secured session, what action does the CSCF take if the target has an ongoing IMS media secured session?
Option 1: The CSCF immediately terminates the ongoing IMS session to restart with interception capabilities.
Option 2: The CSCF ignores the existing session and only intercepts new IMS sessions initiated by the target.
Option 3: The CSCF provides a 'Start of interception with established IMS session' event message to the DF2/MF over the X2 interface.
Option 4: The CSCF directly contacts the Key Management System (KMS) to resolve any MIKEY-TICKET without notifying DF2/MF.
Explanation: When Lawful Interception is activated for a target already engaged in an IMS media secured session, the Communication Service Control Function (CSCF) needs to facilitate the interception of this ongoing session. To do so, it sends a 'Start of interception with established IMS session' event message to the Delivery Function 2/Management Function (DF2/MF) over the X2 interface. This step is crucial for initiating the process to decrypt the content of the communication, which may involve resolving a MIKEY-TICKET and retrieving session keys from the Key Management System (KMS).