Question: What is the condition for the serving NG-RAN node to initiate the Connection Inactive procedure?
Option 1: When the UE is in CM-IDLE state.
Option 2: When the UE is in CM-CONNECTED with RRC_IDLE state.
Option 3: When the UE is in CM-CONNECTED with RRC_CONNECTED state and has received the "RRC Inactive Assistance Information" from the AMF.
Option 4: When the NG-RAN node receives a request from the AMF to initiate the procedure.
Explanation: The serving NG-RAN node can initiate the Connection Inactive procedure only when the UE is in CM-CONNECTED with RRC_CONNECTED state and has received the "RRC Inactive Assistance Information" from the AMF, as defined in clause 5.3.3.2.5 of TS 23.501. This ensures that the NG-RAN node has the necessary information to transition the UE to RRC_INACTIVE state.