Question: During an inter NG-RAN Handover procedure without a change of UPF, what action does the SMF take to indicate to the UPF to switch the N3 path(s) and send end marker packet(s)?
Option 1: The SMF sends an N4 Session Establishment Request message with the new AN Tunnel Info of NG RAN.
Option 2: The SMF sends an N4 Session Modification Request message with the old AN Tunnel Info of NG RAN.
Option 3: The SMF sends an N4 Session Modification Request message with the new AN Tunnel Info of NG RAN and an indication to send end marker packet(s) on the old N3 user plane path.
Option 4: The SMF sends an N9 Session Establishment Request message with the new CN Tunnel Info of the UPF terminating N3.
Explanation: According to the 3GPP TS 23.501 specification, during an inter NG-RAN Handover procedure without a change of UPF, the SMF sends an N4 Session Modification Request message with the new AN Tunnel Info of NG RAN and provides an indication to the UPF to send end marker packet(s) on the old N3 user plane path. This action allows the UPF to switch the N3 path(s) and construct end marker packet(s) for each N3 GTP-U tunnel towards the source NG RAN after sending the last PDU on the old path.