5.8.5.1 General

These parameters are used by SMF to control the functionality of the UPF as well as to inform SMF about events occurring at the UPF.

The N4 session management procedures defined in clause 4.4.1 of TS 23.502 [3] will use the relevant parameters in the same way for all N4 reference points: the N4 Session Establishment procedure as well as the N4 Session Modification procedure provide the control parameters to the UPF, the N4 Session Release procedure removes all control parameters related to an N4 session and the N4 Session Level Reporting procedure informs the SMF about events related to the PDU Session that are detected by the UPF.

The parameters over N4 reference point provided from SMF to UPF comprises an N4 Session ID and may also contain:

• Packet Detection Rules (PDR) that contain information to classify traffic (PDU(s)) arriving at the UPF;
• Forwarding Action Rules (FAR) that contain information on whether forwarding, dropping or buffering is to be applied to a traffic identified by PDR(s);
• Multi-Access Rules (MAR) that contain information on how to handle traffic steering, switching and splitting for a MA PDU Session;
• Usage Reporting Rules (URR) contains information that defines how traffic identified by PDR(s) shall be accounted as well as how a certain measurement shall be reported;
• QoS Enforcement Rules (QER), that contain information related to QoS enforcement of traffic identified by PDR(s);
• Session Reporting Rules (SRR) that contain information to request the UP function to detect and report events for a PDU session that are not related to specific PDRs of the PDU session or that are not related to traffic usage measurement.
• Trace Requirements;
• Port Management Information Container in 5GS;
• Bridge/Router Information.

The N4 Session ID is assigned by the SMF and uniquely identifies an N4 session.

If the UPF indicated support of Trace, the SMF may activate a trace session during a N4 Session Establishment or a N4 Session Modification procedure. In that case it provides Trace Requirements to the UPF. The SMF may deactivate an on-going trace session using a N4 Session Modification procedure. There shall be at most one trace session activated per N4 Session at a time.

For the MA PDU Session, the SMF may add an additional access tunnel information during an N4 Session Modification procedure by updating MAR with addition of an FAR ID which refers to an FAR containing the additional access tunnel information for the MA PDU session for traffic steering in the UPF. For the MA PDU Session, the SMF may request Access Availability report per N4 Session, during N4 Session Establishment procedure or N4 Session Modification procedure.

A N4 Session may be used to control both UPF and NW-TT behaviour in the UPF. A N4 session support and enable exchange of bridge/router configuration between the SMF and the UPF:

• Information that the SMF needs for bridge/router management (clause 5.8.5.9);
• Information that 5GS transparently relays between the TSN AF or TSCTSF and the NW-TT: transparent Port Management Information Container along with the associated NW-TT port number.
• Information that 5GS transparently relays between the TSN AF or TSCTSF and the NW-TT: transparent user plane node Management Information Container (clause 5.8.5.14).

When a N4 Session related with bridge/router management is established, the UPF allocates a dedicated port number for the PDU Session. The UPF then provides to the SMF following configuration parameters for the N4 Session:

• port number.
• user-plane node ID.

To support TSN, the user-plane node ID is Bridge ID. To support integration with IETF DetNet, the user-plane node ID can be Router ID. The User Plane Node ID may be pre-configured in the UPF based on deployment.

After the N4 session has been established, the SMF and UPF may at any time exchange transparent user plane node and Port Management Information Container over a N4 session.