Question: What action should an MME (Mobility Management Entity) take when receiving a Forward Relocation Request message indicating GSM security mode (containing a Kc) for a non-emergency call procedure during handover from a source SGSN to E-UTRAN?
Option 1: Proceed with the handover, ignoring the GSM security mode indication.
Option 2: Initiate an emergency call setup to prioritize the subscriber's access.
Option 3: Request additional security credentials from the subscriber before proceeding.
Option 4: Abort the non-emergency call procedure and respond with an appropriate failure cause.
Explanation: To maintain security integrity and adhere to specified security architectures (as outlined in 3GPP System Architecture Evolution; Security architecture), the MME must prevent GSM subscribers from accessing EPS (Evolved Packet System) via handovers when only GSM security mode is indicated. Aborting the procedure with a failure cause ensures compliance with these security objectives, safeguarding the network from potential vulnerabilities associated with mixed security modes during handover scenarios.