Question: In a scenario where a UE attempts to set up an IMS Emergency Session, and authentication with the MME fails, what action will the MME take if the serving network policy supports unauthenticated IMS Emergency Sessions?
Option 1: The MME will reject the EPS emergency bearer setup request due to authentication failure.
Option 2: The MME will send a NAS SMC with previously announced non-NULL algorithms to the UE for security context establishment.
Option 3: The MME will send a NAS SMC with NULL algorithms to the UE, allowing for an unauthenticated emergency bearer setup.
Option 4: The MME will request additional authentication vectors from the HSS before proceeding.
Explanation: When the serving network policy supports unauthenticated IMS Emergency Sessions and authentication fails, the MME accommodates the emergency session by not enforcing full authentication. Thus, it sends a Non-Access Stratum Security Mode Command (NAS SMC) with NULL algorithms, which effectively allows for the setup of an unauthenticated EPS emergency bearer, prioritizing the emergency communication over the failed authentication.