Question: What is the primary purpose of the MBMS Enquiry Function in the UTRAN Iu interface, initiated by the RNC towards the SGSN, in relation to a specific UE and MBMS bearer service?
Option 1: To request QoS (Quality of Service) adjustments for an ongoing MBMS session.
Option 2: To retrieve the UE's current location for targeted MBMS transmissions.
Option 3: To obtain either the list of MBMS bearer services the UE has joined or the IP Multicast Address and APN corresponding to a given MBMS bearer service.
Option 4: To trigger the setup of a new dedicated channel for MBMS content delivery.
Explanation: The correct answer, Option 3, aligns with the described functionality of the MBMS Enquiry Function. This function is specifically designed to allow the RNC to query the SGSN about two key aspects related to a UE's participation in MBMS services: Firstly, it can request the list of MBMS bearer services that a given UE has explicitly 'joined'. This is crucial for managing and updating the UE's subscription status across different MBMS services. Secondly, for a specified MBMS bearer service, it can ask for the associated IP Multicast Address and Access Point Name (APN), as defined in the relevant MBMS architectural specifications. These details are vital for correctly routing and delivering multicast content to subscribed UEs. The other options (1, 2, and 4) do not accurately reflect the primary purpose of the MBMS Enquiry Function as outlined, involving unrelated aspects such as QoS adjustments, location retrieval, or dedicated channel setup.