Constructing the End Marker Packets through UPF

At the time of the handover procedure, the PDU session for the UE – which comprises of an UPF node – acts as a PDU session anchor and an intermediate UPF terminating N3 reference point. The SMF sends an N4 Session Modification Request message with the new AN Tunnel Info of NG RAN to specify the UPF to switch to the N3 paths. In addition, the SMF also specifies the UPF to send the End Marker packets on the old N3 user plane path.

After the UPF receives the indication, the End Markers are constructed and sent to each N3 GTP-U tunnel toward the source NG RAN, after sending the last PDU on the old path.