Question: What action should an MME take when receiving an MM context in a Context Response indicating GSM security mode during idle mode mobility from a source SGSN?
Option 1: Proceed with the procedure, attempting to authenticate the subscriber using GSM security protocols.
Option 2: Abort the procedure, acknowledging the Context Response from the SGSN with an appropriate failure cause.
Option 3: Request additional security context from the source SGSN to attempt a secure handover.
Option 4: Automatically upgrade the security mode to a more secure protocol (e.g., LTE's EPS security) for the subscriber.
Explanation: This action ensures security and adheres to specified protocols. Allowing a GSM subscriber to access E-UTRAN via idle mode mobility poses security risks due to GSM's less secure nature compared to EPS. Aborting prevents potential breaches, aligning with the security objective of preventing unauthorized access.