Question: What is the purpose of the UE CONTEXT MODIFICATION REQUEST message sent by the gNB-CU to the source gNB-DU in step 7 of the inter-gNB-DU mobility procedure using MCG SRB in EN-DC?
Option 1: To query the latest SCG configuration
Option 2: To indicate to stop the data transmission to the UE and request Downlink Data Delivery Status frame
Option 3: To create an UE context and setup one or more data bearers
Option 4: To release the UE context
Explanation: The gNB-CU sends a UE CONTEXT MODIFICATION REQUEST message to the source gNB-DU in step 7, indicating to stop the data transmission to the UE. This is done to ensure that no further data is sent to the UE from the source gNB-DU after the handover procedure has started. Additionally, the source gNB-DU also sends a Downlink Data Delivery Status frame to inform the gNB-CU about the unsuccessfully transmitted downlink data to the UE.