Question: Under what circumstances shall a UE (User Equipment) apply the MCCH (Multicast Control Channel) information acquisition procedure to receive MBS (Multimedia Broadcast Services) broadcast services?
Option 1: Only upon power-on, when entering a cell providing SIB20 (System Information Block 20).
Option 2: Upon receiving SIB20 of an SCell via dedicated signalling, and also when notified of MCCH information changes due to new MBS services or modifications.
Option 3: Exclusively when the UE is within the MBS service area as indicated by the cell/tracking area list in the USD (User Data).
Option 4: Only after discontinuing all ongoing data transmissions via broadcast MRB (Media Broadcast Multicast Service).
Explanation: This option correctly encompasses multiple scenarios under which a UE must initiate the MCCH information acquisition procedure to ensure it can receive MBS broadcast services. These include not just the initial entry into a cell providing SIB20, but also when dedicated signalling updates are received for an SCell, and crucially, upon notifications of changes to MCCH information.