Question: What is the primary purpose of the MBMS UE Linking Request message in UTRAN's Iu interface, and which network elements are involved in its transmission?
Option 1: To establish a new dedicated channel for a UE, transmitted from RNC to CN.
Option 2: To inform the RNC about a UE's change in multicast service subscription, with transmission from CN to RNC over a connectionless bearer.
Option 3: To notify the RNC that a UE has joined or left one or several Multicast Services, transmitted from CN to RNC using a connection-oriented signalling bearer.
Option 4: To release resources for a UE no longer requiring multicast services, sent from RNC to CN.
Explanation: The MBMS UE Linking Request message updates the RNC about changes in a UE's subscription to Multicast Services. This message is sent by the Core Network to the RNC, utilizing a connection-oriented signalling bearer for reliability.