Question: In an MBMS (Multimedia Broadcast/Multicast Service) registration procedure, what is the primary purpose of including the 'ServiceID' attribute in the RegistrationRequest element?
Option 1: To uniquely identify the User Equipment (UE) for billing purposes.
Option 2: To specify the preferred language for the user service description.
Option 3: To contain the unique MBMS User Service Identifier for service access.
Option 4: To provide an alternative to MSISDN for subscriber identification.
Explanation: The 'ServiceID' attribute contains the unique MBMS User Service Identifier, crucial for the UE to access the specific MBMS user service it has registered for, highlighting its role in service access rather than billing, language preference, or alternative subscriber identification.