Question: In MR-DC (Multi-RAT Dual Connectivity), when a UE (User Equipment) performs a successful random access attempt known only by the Secondary Node (SN), how may the SN inform the Master Node (MN) about this occurrence?
Option 1: Via dedicated X2/Xn signaling for each successful attempt
Option 2: Through periodic UE state reporting from SN to MN
Option 3: Via a RACH (Random Access Channel) indication sent from the SN to the MN
Option 4: By triggering a handover procedure to update the MN
Explanation: In MR-DC scenarios, when the Secondary Node (SN) is aware of successful random access attempts not known by the Master Node (MN), such as for beam failure recovery or UL synchronization issues, it uses a specific mechanism to inform the MN. This is achieved through a RACH indication, which is a signaling message sent from the SN to the MN, indicating the occurrence of these successful random access procedures. This allows the MN to retrieve relevant RA Reports from the UE if necessary, ensuring coordinated management across the dual connectivity setup.