Question: What is the expected behavior of the MME when it receives a SECURITY MODE COMPLETE message from the UE without confidentiality protection, assuming a non-EEA0 (e.g., EEA1, EEA2, etc.) confidentiality algorithm was selected?
Option 1: The MME accepts the message and proceeds with the session establishment.
Option 2: The MME rejects the message due to the absence of confidentiality protection.
Option 3: The MME requests the UE to retransmit the message with a different integrity protection algorithm.
Option 4: The MME ignores the security mode and continues with a default security configuration.
Explanation: According to the NAS confidentiality protection requirement, if a confidentiality algorithm other than EEA0 (no encryption) is selected, the message must be ciphered. Receiving a SECURITY MODE COMPLETE message without confidentiality protection when a non-EEA0 algorithm was chosen indicates a security protocol violation. Thus, the MME, to maintain security integrity, would reject the message, ensuring that only properly secured communications are established.