Section: 4.4.2.2 N4 Session Level Reporting Procedure
Content: This procedure is used by the UPF to report events related to an N4 session for an individual PDU Session. The triggers for event reporting were configured on the UPF during N4 Session Establishment/Modification procedures by the SMF. Figure 4.4.2.2-1: N4 Session Level Reporting procedure 1. The UPF detects that an event has to be reported. The reporting triggers include the following cases: (1) Measurement information reporting (Usage Report). Measurement information shall be collected in the UPF and reported to the SMF as defined in clause 5.8 and clause 5.12 of TS 23.501[ System architecture for the 5G System (5GS) ]  [2]. NOTE 1: The Usage Report is also used for the reporting of other events or information. For details refer to clause 7.5.8.3 of TS 29.244[ Interface between the Control Plane and the User Plane nodes ]  [69]. (2) Start of traffic detection (Usage Report). When traffic detection is requested by SMF and the start of traffic is detected for a Packet Detection Rule (PDR) as described in clause 5.8 of TS 23.501[ System architecture for the 5G System (5GS) ]  [2], the UPF shall report the start of traffic detection to the SMF and indicate the corresponding PDR rule ID. (3) Stop of traffic detection (Usage Report). When traffic detection is requested by SMF and the end of traffic is detected for a PDR as described in clause 5.8 of TS 23.501[ System architecture for the 5G System (5GS) ]  [2], the UPF shall report the stop of traffic detection to the SMF and indicate the corresponding PDR rule ID. (4) Detection of 1st downlink packet for a QoS Flow of a PDU Session with UP Connection deactivated (Downlink Data Report). When UPF receives the first downlink packet for a QoS Flow but no N3/N9 tunnel for downlink data transmission exists and the buffering is performed by the UPF, it shall report the detection of 1st downlink packet to SMF also indicating the QoS Flow for which the downlink packet was received (for the purpose of downlink data notification). The UPF shall also report the DSCP of the packet if the PDU Session type is IP (to support the Paging Policy Differentiation feature described in clause 5.4.3 of TS 23.501[ System architecture for the 5G System (5GS) ]  [2]). (5) Detection of PDU Session Inactivity for a specified period (User Plane Inactivity Report). When an Inactivity Timer for a PDU Session is provided by SMF during N4 Session Establishment/Modification procedure and the UPF detects the PDU Session has no data transfer for a period specified by the Inactivity Timer, it shall report PDU Session Inactivity to the SMF. NOTE 2: As described in clause 4.3.7, an Inactivity Timer to the UPF is not provided by the SMF for always-on PDU Sessions. (6) QoS Monitoring Report (Session Report). When the QoS Monitoring is enabled for the QoS Flow, performs the necessary actions as described in clause 5.45 of TS 23.501[ System architecture for the 5G System (5GS) ]  [2]. The details about when and how the UPF sends the QoS Monitoring reports are described in clause 5.8.2.18 of TS 23.501[ System architecture for the 5G System (5GS) ]  [2]. When receiving the QoS monitoring reports from the UPF, the SMF sends the reports to the target NF according to the information for QoS Monitoring received in the PCC rules as described in TS 23.503[ Policy and charging control framework for the 5G System (5GS); Stage 2 ]  [20]. (7) TSC Management Information available (TSC Management Information). When TSC management information is available, the UPF shall provide the TSC management information in the TSC Management Information to the SMF as defined in clause 5.8.5.14 of TS 23.501[ System architecture for the 5G System (5GS) ]  [2]. (8) Discard Downlink Traffic detection (Downlink Data Report). When discarded downlink traffic detection is requested by SMF for a PDR and the first downlink packet is discarded after being buffered for this PDR as described in clause 5.8.3.2 of TS 23.501[ System architecture for the 5G System (5GS) ]  [2], the UPF shall report the discarded downlink traffic detection to the SMF and indicate the corresponding PDR rule ID (for the purpose of downlink data delivery status notification). (9) Buffered Downlink Traffic detection (Downlink Data Report). When buffered downlink traffic detection is requested by SMF for a PDR and the first downlink packet is buffered for this PDR as described in clause 5.8.3.2 of TS 23.501[ System architecture for the 5G System (5GS) ]  [2], the UPF shall report the buffered downlink traffic detection to the SMF and indicate the corresponding PDR rule ID (for the purpose of downlink data delivery status notification). (10) N6 Traffic Parameter Measurement Report (Session Report). When the N6 Traffic Parameters measurement report is requested by SMF for a QoS Flow as described in clause 5.37.8.2 of TS 23.501[ System architecture for the 5G System (5GS) ]  [2], the UPF shall report to the SMF the N6 Traffic Parameter(s) for the specified QoS Flow (i.e. the N6 jitter range associated with the DL periodicity and conditionally, the UL/DL periodicity). 2. The UPF sends an N4 session report message (N4 Session ID, list of [Usage Report, Downlink Data Report, Session Report, User Plane Inactivity Report, TSC Management Information]) to the SMF. 3. The SMF identifies the N4 session context based on the received N4 Session ID and applies the reported information for the corresponding PDU Session. The SMF responds with an N4 session report ACK message.