Question: During an ECM-IDLE to ECM-CONNECTED transition, what happens if no current EPS NAS security context exists for integrity protection of the initial NAS message?
Option 1: The UE generates a new KASME without an AKA run.
Option 2: The MME applies default security settings for the transition.
Option 3: The eNB denies the transition to ECM-CONNECTED state.
Option 4: The UE signals 'no key available' in the initial NAS message.
Explanation: When transitioning from ECM-IDLE to ECM-CONNECTED, if there's no existing EPS NAS security context for integrity protection, the UE must indicate this absence of security material. Signaling 'no key available' informs the network about the need for potential re-establishment or transfer of security contexts, ensuring secure communication can be initiated.