The invocation-related priority mechanisms for prioritized services are based on interaction with an Application Server and between the Application Server and the PCF over Rx/N5 interface (as described in TS 23.228 clause 5.21 in the case of MPS using IMS).

Invocation-related mechanisms for Mobile Originations (for example, via SIP/IMS) are explained below:

• PCF:

  • When an indication for a session arrives over the Rx/N5 interface and the UE does not have priority for the signaling QoS Flow, the PCF derives the ARP and 5QI parameters plus associated QoS characteristics as appropriate, as per the Service Provider policy (specified in clause 6.1.3.11 of TS 23.503).

  • For MPS sessions, when establishing or modifying a QoS Flow 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 Flows.

  • When all active sessions to a particular DN are released and the UE is not configured for priority treatment to that particular PDU session, the PCF downgrades the IMS Signaling 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.

Invocation-related mechanisms for Mobile Terminations (for example, via SIP/IMS) are explained below:

• PCF: When an indication for a session arrives over the Rx/N5 interface, the 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 (specified in clause 4.2.3.3 of TS 23.502).

• SMF: If a "Data Notification" message arrives at the SMF for a QoS Flow associated with an ARP priority level value for priority use, delivery of priority indication during the Paging procedure is provided by inclusion of the ARP in the N11 interface "N1N2MessageTransfer" message (specified in clause 4.2.3.3 of TS 23.502).

• AMF: If an "N1N2MessageTransfer" message arrives at the AMF containing an ARP priority level value for priority use, 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 entitled to priority treatment (specified in clause 4.2.3.3 of TS 23.502).

• 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 for priority use, the SMF sends an "N1N2MessageTransfer" to update the ARP for the Signaling QoS Flows (specified in clause 4.3.3.2 of TS 23.502).

• AMF: Upon receiving the "N1N2MessageTransfer" message from the SMF with an ARP priority level for priority use, the AMF updates the ARP for the Signaling QoS Flows (specified in clause 4.3.3.2 of TS 23.502).

• (R)AN: Inclusion of the "Paging Priority" in the N2 "Paging" message triggers priority handling of paging in times of congestion at the (R)AN (specified in clause 4.2.3.3 of TS 23.502).

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 Flows 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 (specified in clause 4.3.3 of TS 23.502).

  • If the state of Priority PDU connectivity services is modified from enabled to disabled, the QoS Flows controlled by the Priority PDU connectivity services are modified from 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 (specified in clause 4.3.3 of TS 23.502).

An overloaded node performs message prioritization when handling incoming messages during an overloaded condition based on the relative GTP-C message priority signaled in the GTP-C header.

When message throttling is performed:

• GTP requests related to priority traffic (eMPS as described in 3GPP TS 22.153) and emergency have the highest priority. Depending on regional/national requirements and network operator policy, these GTP requests are the last to be throttled when applying traffic reduction. The priority traffic is exempted from throttling due to GTP overload control up to the point where the requested traffic reduction cannot be achieved without throttling the priority traffic.

• For other types of sessions, message throttling considers the relative priority of the messages so that low priority messages are considered for throttling before the other messages. The relative priority of the messages is derived from the relative priority of the procedure for which the message is being sent (as specified in clause 12.3.9.3.2) or derived from the session parameters such as APN and ARP.

The high priority messages are given lower preference to throttle and low priority messages are given higher preference to throttle. An overloaded node also applies these message prioritization schemes when handling incoming initial messages during an overloaded condition, as part of the self-protection mechanism.

A sending GTP-C entity determines the relative message priority to signal in the message according to either procedure based or session parameters. If the message affects multiple bearers (for example, Modify Bearer Request), the relative message priority considers the highest priority ARP among all the bearers.

A GTP-C entity sets the same message priority in a Triggered message or Triggered Reply message as received in the corresponding Initial message or Triggered message respectively. For incoming GTP-C messages that do not have a message priority in the GTP-C header, the receiving GTP-C entity:

• Applies a default priority if the incoming message is an Initial message.

• Applies the message priority sent in the Initial message or Triggered message if the incoming message is a Triggered or Triggered Reply message respectively.

The nodes in the network homogenously support this feature; otherwise an overloaded node processes initial messages received from the non-supporting nodes according to the default priority and processes initial messages received from the supporting nodes according to the message priority signaled in the GTP-C message.

Message-Prioritization based on Session Parameters

Message prioritization is also performed based on the session parameters such as APN and ARP. The procedures and messages associated with the higher priority sessions are given lesser preference while throttling, as compared to the procedures and messages associated with the lower priority sessions. Within each group of sessions, the messages are further prioritized based on the category of the procedure for which the message is being sent.

When the message throttling is performed:

• PFCP requests related to priority traffic (that is, eMPS as described in 3GPP TS 22.153) and emergency have the highest priority. Depending on regional/national requirements and network operator policy, these PFCP requests are the last to be throttled when applying traffic reduction. Throttling exempts the priority traffic due to PFCP overload control up to the point where the requested traffic reduction cannot be achieved without throttling the priority traffic.

• For other types of sessions, the message throttling considers the relative priority of the messages so that the messages with low priority are first considered for the throttling. The relative priority of the messages is derived from the relative priority of the procedure for which the message is being sent or derived from the session parameters such as APN and ARP.

An overloaded node (UPF, SMF) may apply these message prioritization schemes when handling incoming initial messages during an overloaded condition, as part of a self-protection mechanism. Incoming messages are handled during an overloaded condition based on the relative PFCP message priority signaled in the PFCP header.

A PFCP entity determines whether to set and use the message priority in PFCP signalling, based on operator policy. A sending PFCP entity determines the relative message priority to signal in the message which are derived from the session parameters such as APN and ARP. If the message affects multiple bearers, the relative message priority is determined considering the highest priority ARP among all the bearers. A PFCP entity must set the same message priority in a Response message as received in the corresponding Request message.

For incoming PFCP messages that do not have a message priority in the PFCP header, the receiving PFCP entity:

• Applies a default priority if the incoming message is a Request message.

• Applies the message priority sent in the Request message if the incoming message is a Response message.

The SMF and UPF functions in the network homogenously support this feature; otherwise an overloaded node will process the Request messages received from the non-supporting nodes according to the default priority and Request messages received from supporting nodes will be processed according to the message priority signalled in the PFCP message.