5G(NR) RAN Learning -- PDU Session Resource Notification

I. PDU Session Resource Notification (PDU SESSION RESOURCE NOTIFY) is a 5G system notification to the core network element AMF that a QoS flow or PDU session established for a specific terminal (UE) has been released, is no longer being executed, or is being re-executed by an NG-RAN node controlled by a request notification. This procedure is also used to notify the NG-RAN node of QoS parameters that were not successfully accepted during the path handover request procedure. The entire procedure uses UE-related signaling.

II. PDU Session Resource Success Notification: As shown in Figure 8.2.4.2-1, the PDU session resource success operation is initiated by the GN-RAN node.

III. Key information for PDU session resource notification includes:

• The NG-RAN node initiates this process by sending a PDU session resource notification message.
• The PDU SESSION RESOURCE NOTIFY message should contain information about PDU session resources or QoS flows that have been released, are no longer being executed, or have been re-executed by the NG-RAN node.
• For each PDU session where some QoS flows have been released, are no longer being executed, or have been re-executed by the NG-RAN node, a PDU session resource notification transport IE should be included, containing:
• A list of QoS flows released by the NG-RAN node (if any) in the QoS flow release list IE. If no other QoS flows are associated with the existing bearer after release (e.g., splitting the PDU session), the NG-RAN node and 5GC should consider the associated NG-U transport bearer to have been removed, and the associated NG-U UP TNL information to be available again.
• A list of GBR QoS flows that the NG-RAN node no longer executes or has re-executed by the NG-RAN node (if any) in the QoS flow notification list IE, along with the notification reason IE. For QoS flows indicated as no longer satisfied, the NG-RAN node may also indicate the alternative QoS parameter sets that can currently be satisfied in the Current QoS Parameter Set Index IE. For QoS flows indicated as no longer satisfied, the NG-RAN node may also indicate RAN feedback in the TSC Traffic Characteristics Feedback IE.
• A list (if any) of QoS flows whose QoS parameters have been updated but cannot be successfully accepted by the NG-RAN node during a path handover request should be included in the QoS Flow Feedback List IE, which may be associated with values ​​that can be provided.
• For each PDU session resource released by the NG-RAN node, a PDU session resource notification transmission released should be included in the "PDU Session Resource Notification Released Transmission IE" and the release reason should be included in the "Reason IE". If the User Plane Error Indication IE is set to "Received GTP-U Error Indication", the SMF (if supported) should consider the PDU session released due to receiving a GTP-U error indication through the NG-U tunnel, as described in TS 23.527.
• The NG-RAN node (if supported) should report the UE location information in the User Location Information IE in the PDU SESSION RESOURCE NOTIFY message.
• Upon receiving a PDU SESSION RESOURCE NOTIFY message, the AMF should transparently transmit a PDU Session Resource Notify Transfer IE or a PDU Session Resource Notify Released Transfer IE to the SMF associated with the relevant PDU session for each PDU session indicated in the PDU Session ID IE.
• Upon receiving the PDU Session Resource Notify Transfer IE, the SMF typically initiates the corresponding release or modification procedure on the core network side for PDU sessions or QoS flows that are identified as no longer satisfying.
• For each PDU session, if its PDU Session Resource Notification Transfer IE or PDU Session Resource Notification Released Transfer IE contains a Secondary RAT Usage Information IE, the SMF should process this information in accordance with TS 23.502.
• If the PDU Session Resource Notification message contains a User Location Information IE, the AMF should process this information in accordance with TS 23.501.