5.37.5.2 PDU Set Information and Identification

To support PDU Set based Handling, the PSA UPF identifies PDUs that belong to a PDU Set and determines the below PDU Set Information and sends it to the 5G-AN in the GTP-U header. The PDU Set Information is used by the 5G-AN for PDU Set based Handling as described above.

The PDU Set Information comprises:

• PDU Set Sequence Number.
• Indication of End PDU of the PDU Set.
• PDU Sequence Number within a PDU Set.
• PDU Set Size in bytes.
• PDU Set Importance, which identifies the relative importance of a PDU Set compared to other PDU Sets within a QoS Flow.

The 5G-AN may use the Priority Level (see clause 5.7.3.3) across QoS Flows and PDU Set Importance within a QoS Flow for PDU Set level packet discarding in presence of congestion.

NOTE 1: In addition to considering the PDU Set Importance within a QoS Flow, 5G-AN could also consider the relative PDU Set Importance across QoS Flows of the same Priority Level when determining which PDU Set needs to be discarded, which is up to implementation and configuration of operator.

NOTE 2: The PDU Set Information can be different for different PDU Sets within a QoS Flow.

If the 5G-AN has provided a PDU Set Based Handling Support Indication indicating that PDU Set based Handling is supported and a DL Protocol Description together with 1) a PSIHI and/or 2) PSDB and PSER is included in the PCC rule, the SMF instructs PSA UPF to perform PDU Set marking and may provide the PSA UPF the DL Protocol Description used by the service data flow. The DL Protocol Description may be received in the PCC rule, based on information provided by the AF or by PCF local policies as described in clause 5.37.5.1.

If the DL PDU Set Information Marking Support Indication has been sent to the 5G-AN (as described in clause 5.37.5.1) and the 5G-AN has provided a PDU Set Based Handling Support Indication indicating that PDU Set based Handling is supported, the SMF instructs PSA UPF to perform PDU Set marking and provides the PSA UPF the DL Protocol Description used by the service data flow.

The SMF instructs the PSA UPF to perform PDU Set marking by providing the PDU Set Information marking Indicator in the QER. If the PCC rule contains the parameter PDU Set Importance for N6-unmarked PDUs (see clauses 6.1.3.27.4 and 6.3.1 of TS 23.503 [45]), the SMF shall forward this parameter in the QER.

PSA UPF can identify the PDU Set Information using the DL Protocol Description and the received transport protocol headers and payload or using implementation specific means. The details of the RTP/SRTP headers, header extensions and/or payloads used to identify PDU Set Information are defined in TS 26.522 [179].

For end-to-end encrypted traffic, PDU Set Information is received as media related information from the Application Server, see clause 5.37.9.

For each DL PDU received on N6 for which PDU Set Information marking Indicator is indicated from the SMF, the PSA UPF applies the rules for PDU Set identification and provides the available PDU Set Information to the 5G-AN in the GTP-U header.

NOTE 3: The PSA UPF is expected to assign a unique PDU Set Sequence Number in the GTP-U header to each PDU Set of the QoS Flow.