Question: What action must a UE take before requesting missing MBMS keys from the BM-SC, according to the MBMS Key Management Function protocols?
Option 1: Establish a secure connection with the cellular network using TLS
Option 2: Register with the Key Request subfunction of the Key Management function, specifying the MBMS User Service
Option 3: Authenticate with the BM-SC using its IMSI (International Mobile Subscriber Identity)
Option 4: Send a deregistration request for all existing MBMS services
Explanation: This is correct because, as per the MBMS Key Management Function protocols, before a UE can request missing MBMS keys from the BM-SC, it must first register with the Key Request subfunction of the Key Management function. This registration requires the UE to indicate the specific MBMS User Service it wishes to access, ensuring that key distribution is managed securely and efficiently for authorized users only.