5.22.3 Invocation-related Priority Mechanisms

The generic mechanisms used based on invocation-related Priority Mechanisms for prioritised services are based an interaction with an Application Function and between the Application Function and the PCF over Rx/N5 interface.

These mechanisms apply to mobile originated as well as mobile terminated SIP call/sessions (clause 5.21 of TS 23.228 [15]) and Priority PDU connectivity services including MPS for Data Transport Service.

NOTE 1: Clause 5.21 of TS 23.228 [15] is applicable to 5GS, with the understanding that the term PCRF corresponds to PCF in the 5GS.

Invocation-related mechanisms for Mobile Originations e.g. via SIP/IMS:

• PCF: When an indication for a session arrives over the Rx/N5 Interface and the UE does not have priority for the signalling QoS Flow, the PCF derives the ARP and 5QI parameters, plus associated QoS characteristics as appropriate, of the QoS Flow for Signalling as per Service Provider policy as specified in clause 6.1.3.11 of TS 23.503 [45].
• PCF: For sessions such as MPS, when establishing or modifying a QoS Flow for media as part of the session origination procedure, the PCF selects the ARP and 5QI parameters, plus associated QoS characteristics as appropriate, to provide priority treatment to the QoS Flow(s).
• PCF: When all active sessions to a particular DN are released and the UE is not configured for priority treatment to that particular PDU Session for a DN, the PCF will downgrade the IMS Signalling QoS Flows from appropriate settings of the ARP and 5QI parameters, plus associated QoS characteristics as appropriate, to those entitled by the UE based on subscription.
• SMF/AMF: Based on the QoS parameters (e.g. ARP, 5QI) of a PDU Session, the SMF may provide a PDU Session Priority to the AMF. The AMF stores the information for further PDU Session related priority handling (i.e. for determination of Message Priority header of subsequent message related to the PDU Session).

Invocation-related mechanisms for Mobile Terminations e.g. via SIP/IMS:

• PCF: When an indication for a session arrives over the Rx/N5 Interface, mechanisms as described above for Mobile Originations are applied.
• UPF: If an IP packet arrives at the UPF for a UE that is CM-IDLE, the UPF sends a "Data Notification" including the information to identify the QoS Flow for the DL data packet to the SMF, as specified in clause 4.2.3.3 of TS 23.502 [3].
• SMF: If a " Data Notification" message arrives at the SMF for a QoS Flow associated with an ARP priority level value that is entitled for priority use, delivery of priority indication during the Paging procedure is provided by inclusion of the ARP in the N11 interface "N1N2MessageTransfer" message, as specified in clause 4.2.3.3 of TS 23.502 [3]. Based on the QoS parameters (e.g. ARP, 5QI) of a PDU Session, the SMF may also provide a PDU Session Priority to the AMF.
• AMF: If an "N1N2MessageTransfer" message arrives at the AMF:
• from an SMF containing an ARP priority level value that is entitled for priority use;
• from the SMSF with an MT-SMS related request and either an indication that MPS for Messaging is enabled for the UE from the UDM, or with a Message Priority header value used for MPS for Messaging;

the AMF:

• handles the request with priority and includes the "Paging Priority" IE in the N2 "Paging" message set to a value assigned to indicate that there is an IP packet at the UPF or an MT-SMS at the SMSF entitled to priority treatment, as specified in clause 4.2.3.3 or clause 4.13.3.6 of TS 23.502 [3], when the UE is CM-IDLE; or
• determines the service priority ("RAN Paging Priority" IE as specified in TS 38.413 [34]) and includes the service priority in the N2 Downlink NAS Transport message to the NG-RAN, when the UE is CM-CONNECTED.

If a PDU Session Priority is provided by the SMF, the AMF stores the information for further PDU Session related priority handling (i.e. for determination of Message Priority header of subsequent message related to the PDU Session).

• SMF: For a UE that is not configured for priority treatment, upon receiving the "N7 Session Management Policy Modification" message from the PCF with an ARP priority level that is entitled for priority use, the SMF sends an "N1N2MessageTransfer" to update the ARP for the Signalling QoS Flows, as specified in clause 4.3.3.2 of TS 23.502 [3]. Based on the QoS parameters (e.g. ARP, 5QI) of a PDU Session, the SMF may also provide a PDU Session Priority to the AMF.
• AMF: Upon receiving the "N1N2MessageTransfer" message from the SMF with an ARP priority level that is entitled for priority use, the AMF updates the ARP for the Signalling QoS Flows, as specified in clause 4.3.3.2 of TS 23.502 [3].
• NG-RAN: Inclusion of the "Paging Priority" in the N2 "Paging" message or the "RAN Paging Priority" and ARP value associated with priority service (e.g. MPS) in other N2 messages (e.g. Downlink NAS Transport, PDU Session Resource Setup or Modify message) triggers priority handling of paging, including over Xn interface, in times of congestion at the NG-RAN, as specified in clauses 4.2.3.3, 4.8 and 4.13.3 of TS 23.502 [3], respectively.

Invocation-related mechanisms for the Priority PDU connectivity services:

• PCF: If the state of the Priority PDU connectivity services is modified from disabled to enabled, the QoS Flow(s) controlled by the Priority PDU connectivity services are established/modified to have the service appropriate settings of the ARP and 5QI parameters, plus associated QoS characteristics as appropriate, using the PDU Session Modification procedure as specified in clause 4.3.3 of TS 23.502 [3].
• PCF: If the state of Priority PDU connectivity services is modified from enabled to disabled, the QoS Flow(s) controlled by the Priority PDU connectivity services are modified from Priority PDU connectivity service appropriate settings of the ARP and 5QI parameters, plus associated QoS characteristics as appropriate, to those entitled by the UE as per subscription, using the PDU Session Modification procedure as specified in clause 4.3.3 of TS 23.502 [3].
• SMF/AMF: Based on the QoS parameters (e.g. ARP, 5QI) of a PDU Session, the SMF may provide a PDU Session Priority to the AMF. The AMF stores the information for further PDU Session related priority handling (i.e. for determination of Message Priority header of subsequent message related to the PDU Session).

Invocation-related mechanisms for MPS for Data Transport Service:

• MPS for Data Transport Service follows the same steps as those for Priority PDU connectivity services. The QoS Flows that will be subject to MPS for Data Transport Service are based on operator policy and regulations by means of local PCF configuration.

NOTE 2: If no configuration is provided, MPS for Data Transport Service applies to the QoS Flow associated with the default QoS rule.