3GPP 23.501 v20.2.0 — the document's own text

5.8.2.12 Reporting of the UE MAC addresses used in a PDU Session

Taught in 13. Where the packets actually go (The 5G system architecture, in depth), 5. The connection, and what is promised on it (The 5G system architecture, overview).

For Ethernet PDU Session type, the SMF may control the UPF to report the different MAC (Ethernet) addresses used as source address of frames sent UL by the UE in a PDU Session. These MAC addresses are called UE MAC addresses.

This control and the corresponding reporting takes place over N4.

NOTE: This is e.g. used to support reporting of all UE MAC addresses in a PDU Session to the PCF as described in clause 5.6.10.2.

The UPF reports the removal of a UE MAC address based on the detection of absence of traffic during an inactivity time. The inactivity time value is provided by the SMF to the UPF.