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Content for  TS 23.501  Word version:  19.1.0

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5.22 System Enablers for priority mechanism  5.22.1 General  5.22.2 Subscription-related Priority Mechanisms  5.22.3 Invocation-related Priority Mechanisms  5.22.4 QoS Mechanisms applied to established QoS Flows  5.23 Supporting for Asynchronous Type Communication  5.24 3GPP PS Data Off  5.25 Support of OAM Features  5.25.1 Support of Tracing: Signalling Based Activation/Deactivation of Tracing  5.25.2 Support of OAM-based 5G VN group management  5.25.3 Signalling Based Activation of QoE Measurement Collection  5.26 Configuration Transfer Procedure  5.26.1 Architecture Principles for Configuration Transfer  5.26.2 Addressing, routing and relaying 
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5.22  System Enablers for priority mechanism  p. 356

5.22.1  General  p. 356

The 5GS and the 5G QoS model allow classification and differentiation of specific services such as listed in clause 5.16, based on subscription-related and invocation-related priority mechanisms. These mechanisms provide abilities such as invoking, modifying, maintaining, and releasing QoS Flows with priority, and delivering QoS Flow packets according to the QoS characteristics under network congestion conditions.
Subscription-related Priority Mechanisms include the ability to prioritize flows based on subscription information, including the prioritization of RRC Connection Establishment based on Unified Access Control mechanisms and the establishment of prioritized QoS Flows.
Invocation-related Priority Mechanisms include the ability for the service layer to request/invoke the activation of prioritized QoS Flows through an interaction over Rx/N5 and packet detection in the UPF.
QoS Mechanisms applied to established QoS Flows include the ability to fulfil the QoS characteristics of QoS Flows through preservation of differentiated treatment for prioritized QoS Flow and resource distribution prioritization.
Messages associated with priority services that are exchanged over service-based interfaces may include a Message Priority header to indicate priority information, as specified in TS 23.502 and TS 29.500.
In addition, the separation of concerns between the service classification provided by the core network through the association of Service Data Flows to QoS, and the enforcing of QoS differentiation in (R)AN through the association of QoS Flows to Data Radio bearers, supports the prioritization of QoS Flows when a limitation of the available data radio bearers occurs.
In addition, it also includes the ability for the service layer to provide instructions on how to perform pre-emption of media flows with the same priority assigned through an interaction over Rx as defined in TS 23.503.
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5.22.2  Subscription-related Priority Mechanisms  p. 356

Subscription-related mechanisms which are always applied:
  • (R)AN: During initial Access Network Connection Establishment, the Establishment Cause is set to indicate that special treatment is to be applied by the (R)AN in the radio resource allocation as specified in clause 5.2 for 3GPP access.
  • UDM: As defined in clause 5.2.3 of TS 23.502, the UE subscription data in the UDM contains an MPS subscription indication (i.e. MPS priority indication and optionally MPS for Messaging indication) and an MCX subscription indication (i.e. MCX priority) for the UE that has subscription to MPS and MCX, respectively. The MPS priority and the MCX priority, if available, are provided to the AMF via the Registration or the UE Configuration Update procedure as defined in clause 4.2 of TS 23.502. The MPS for Messaging indication sets(enables)/clears(disables) the MPS priority treatment of Messaging service (i.e. SMS over NAS, SMS over IP and messaging over IMS are all controlled by one indication) for an MPS-subscribed UE. The MPS for Messaging indication is used in communications between NFs and network entities in the CN. The MPS for Messaging indication is not delivered to UE. The MPS for Messaging indication parameter may be provisioned by an AF via NEF as described in clause 4.15.6 of TS 23.502.
  • AMF: Following Access Network Connection Establishment, the receipt of the designated Establishment Cause (i.e. high priority access) by the AMF will result in priority handling of the "Initial UE Message" received as part of the Registration procedures of clause 4.2.2 of TS 23.502. If the AMF did not receive a designated Establishment Cause (i.e. high priority access), but when the AMF determines that there is a MPS priority (or MCX priority) in the UDM for that UE, the AMF shall provide priority handling for that UE at that time and shall provide the MPS priority (or MCX priority) to the UE via the Registration or the UE Configuration Update procedure, as defined in clause 4.2 of TS 23.502. In addition, certain exemptions to Control Plane Congestion and Overload Control are provided as specified in clause 5.19. For the MPS for Messaging indication, the AMF uses the parameter to determine the Message priority header related to SMS delivery and as described in clause 4.13 of TS 23.502.
Subscription-related mechanisms which are conditionally applied:
  • UE: When barring control parameters are broadcast by the RAN, access barring based on Access Identity(es) configured in the USIM and/or an Access Category is applied prior to an initial upstream transmission for the UE which provides a mechanism to limit transmissions from UEs categorized as non-prioritized, while allowing transmissions from UEs categorized as prioritized (such as MPS subscribed UEs), during the RRC Connection Establishment procedure as specified in clause 5.2.
  • UDM: One or more ARP priority levels are assigned for prioritized or critical services. The ARP of the prioritized QoS Flows for each DN is set to an appropriate ARP priority level. The 5QI is from the standard value range as specified in clause 5.7.2.7. In addition, Priority Level may be configured for the standardized 5QIs, and if configured, it overwrites the default value specified in the QoS characteristics Table 5.7.4-1.
  • PCF: The "IMS Signalling Priority" information is set for the subscriber in the UDM, and the PCF modifies the ARP of the QoS Flow used for IMS signalling, for each DN which supports prioritized services leveraging on IMS signalling, to an appropriate ARP priority level assigned for that service.
  • SMF/AMF: Based on the QoS parameters (e.g. ARPs, 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).
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5.22.3  Invocation-related Priority Mechanisms  p. 357

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) and Priority PDU connectivity services including MPS for Data Transport Service.
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.
  • 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.
  • 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. 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 containing an ARP priority level value that is entitled 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, as specified in clause 4.2.3.3 of TS 23.502. 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. 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.
  • (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 as 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 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.
  • 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.
  • 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.
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5.22.4  QoS Mechanisms applied to established QoS Flows  p. 359

Mechanisms applied to established QoS Flows:
  • (R)AN: QoS Flows requested in the Xn "Handover Request" or N2 "Handover Request" which are marked as entitled to priority by virtue of inclusion of an ARP value from the set allocated by the Service Provider for prioritised services are given priority over requests for QoS Flows which do not include an ARP from the set as specified in clause 4.9 of TS 23.502.
  • SMF: Congestion management procedures in the SMF will provide priority to QoS Flows established for sessions during periods of extreme overload. Prioritised services are exempt from any session management congestion controls. See clause 5.19.
  • AMF: Congestion management procedures in the AMF will provide priority to any Mobility Management procedures required for the prioritised services during periods of extreme overload. Prioritised services are exempt from any Mobility Management congestion controls. See clause 5.19.5.
    QoS Flows whose ARP parameter is from the set allocated by the Service Provider for prioritised services' use shall be exempt from release during QoS Flow load rebalancing.
  • (R)AN, UPF: IMS Signalling Packets associated with prioritised services' use are handled with priority. Specifically, during times of severe congestion when it is necessary to drop packets on the IMS Signalling QoS Flow, or QoS Flow supporting MPS for Data Transport Service signalling, to ensure network stability, these FEs shall drop packets not associated with priority signalling such as MPS or Mission Critical services before packets associated with priority signalling. See clause 5.16.5 and clause 5.16.6.
  • (R)AN, UPF: During times of severe congestion when it is necessary to drop packets on a media QoS Flow to ensure network stability, these FEs shall drop packets not associated with priority sessions such as MPS or Mission Critical services before packets associated with priority sessions. See clause 5.16.5 and clause 5.16.6.
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5.23  Supporting for Asynchronous Type Communication  p. 359

Asynchronous type communication (ATC) enables 5GC to delay synchronizing UE context with the UE, so as to achieve an efficient signalling overhead and increase system capacity. The support of ATC is optional for the AMF.
5GC supports asynchronous type communication with the following functionality:
  • Capability to store the UE context based on the received message, and synchronize the UE context with the involved network functions or UE later;
For network function (e.g. PCF, UDM, etc.) triggered signalling procedure (e.g. network triggered Service Request procedure, network triggered PDU Session Modification procedure, etc.), if the UE CM state in the AMF is CM-IDLE state and the requesting network function indicates to the AMF the ATC is allowed for the signalling, if the AMF supports the ATC feature, the AMF may update and store the UE context based on the received message without paging UE immediately. When the UE CM state in the AMF enters CM-CONNECTED state, the AMF forwards N1 and N2 message to synchronize the UE context with the (R)AN and/or the UE.
If the originating NF does not require immediate delivery, it may indicate that the AMF is allowed to use ATC.
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5.24  3GPP PS Data Off  p. 359

This feature, when activated by the user, prevents traffic via 3GPP access of all IP packets, Unstructured and Ethernet data except for those related to 3GPP PS Data Off Exempt Services. The 3GPP PS Data Off Exempt Services are a set of operator services, defined in TS 22.011 and TS 23.221, that are the only allowed services when the 3GPP PS Data Off feature has been activated by the user. The 5GC shall support 3GPP PS Data Off operation in both non-roaming and roaming scenarios.
UEs may be configured with up to two lists of 3GPP PS Data Off Exempt Services and the list(s) are provided to the UEs by HPLMN via Device Management or UICC provisioning. When the UE is configured with two lists, one list is valid for the UEs camping in the home PLMN and the other list is valid for any VPLMN the UE is roaming in. When the UE is configured with a single list, without an indication to which PLMNs the list is applicable, then this list is valid for the home PLMN and any PLMN the UE is roaming in.
The UE reports its 3GPP PS Data Off status in PCO (Protocol Configuration Option) to (H-)SMF during UE requested PDU Session Establishment procedure for establishment of a PDU Session associated with 3GPP access and/or non-3GPP access. The UE does not need to report PS Data Off status during the PDU Session Establishment procedure for handover of the PDU Session between 3GPP access and non 3GPP access if 3GPP PS Data Off status is not changed since the last report. The PS Data Off status for a PDU Session does not affect data transfer over non-3GPP access.
If 3GPP PS Data Off is activated, the UE prevents the sending of uplink IP packets, Unstructured and Ethernet data except for those related to 3GPP PS Data Off Exempt Services, based on the pre-configured list(s) of Data Off Exempt Services.
If 3GPP PS Data Off is activated for a UE with MA PDU Sessions established through the ATSSS feature (see clause 5.32), the data transferred over the non-3GPP access of the MA PDU sessions are unaffected, which is ensured by the policy for ATSSS Control as specified in clause 5.32.3.
The UE shall immediately report a change of its 3GPP PS Data Off status in PCO by using UE requested PDU Session Modification procedure. This also applies to the scenario of inter-RAT mobility to NG-RAN and to scenarios where the 3GPP PS Data Off status is changed when the session management back-off timer is running as specified in clause 5.19.7.3 and clause 5.19.7.4. For UEs in Non-Allowed Area (or not in Allowed Area) as specified in clause 5.3.4.1, the UE shall also immediately report a change of its 3GPP PS Data Off status for the PDU Session. For UEs moving out of LADN area and the PDU Session is still maintained as specified in clause 5.6.5, the UE shall also immediately report a change of its 3GPP PS Data Off status for the PDU Session.
The additional behaviour of the SMF for 3GPP PS Data Off is controlled by local configuration or policy from the PCF as defined in TS 23.503.
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5.25  Support of OAM Features  p. 360

5.25.1  Support of Tracing: Signalling Based Activation/Deactivation of Tracing  p. 360

5GS supports tracing as described in TS 32.421. 5GS support may include subscriber tracing (tracing targeting a SUPI) or equipment tracing (tracing targeting a PEI) but also other forms of tracing further described in TS 32.421 and TS 32.422.
The content of Trace Requirements about a UE (e.g. trace reference, address of the Trace Collection Entity, etc.) is defined in TS 32.421.
Trace Requirements about a UE may be configured in subscription data of the UE and delivered together with other subscription data by the UDM towards the AMF, the SMF and/or the SMSF.
The AMF propagates Trace Requirements about a UE received from the UDM to network entities not retrieving subscription information from UDM, i.e. to the 5G-AN, to the AUSF and to the PCF. The AMF also propagates Trace Requirements to the SMF and to the SMSF. If the I-SMF or V-SMF is needed for the PDU session, the AMF propagates Trace Requirements to the I-SMF or V-SMF. The I-SMF or V-SMF also propagates Trace Requirements received from the AMF to the I-UPF or V-UPF (over N4).
Trace Requirements about a UE may be sent by the AMF to the 5G-AN as part of:
  • the N2 procedures used to move the UE from CM-IDLE to CM-CONNECTED or,
  • the N2 procedures to request a Hand-over from a target NG-RAN or,
  • a stand-alone dedicated N2 procedure when tracing is activated while the UE is CM-CONNECTED.
Trace Requirements about a UE sent to a 5G-AN shall not contain information on the SUPI or on the PEI of the UE. Trace Requirements are directly sent from Source to Target NG-RAN in the case of Xn Hand-Over.
The SMF propagates Trace Requirements about a UE received from the UDM to the UPF (over N4) and to the PCF. The SMF provides Trace Requirements to the PCF when it has selected a different PCF than the one received from the AMF.
Once the SMF or the SMSF has received subscription data, Trace Requirements received from UDM supersede Trace requirements received from the AMF. Trace Requirements are exchanged on N26 between the AMF and the MME.
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5.25.2  Support of OAM-based 5G VN group management |R16|  p. 361

5GS supports 5G LAN-type service as defined in clause 5.29. 5G LAN-type service includes the 5G VN group management that can be configured by a network administrator.
The parameters for 5G VN group is defined in clause 5.29.
The 5G VN group parameters about a UE may be configured in subscription data of the UE and delivered together with other subscription data by the UDM towards the AMF and SMF.
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5.25.3  Signalling Based Activation of QoE Measurement Collection |R17|  p. 361

5GS may support QoE Measurement Collection (QMC) as described in TS 28.405. 5GS may support Signalling based activation and Management based activation as specified in TS 38.300 and TS 28.405.
To enable signalling based activation in NR, the QMC Configuration information is configured in subscription data of the UE. 5GC provides the QMC Configuration information to the NG-RAN as described in TS 23.502.
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5.26  Configuration Transfer Procedure  p. 361

The purpose of the Configuration Transfer is to enable the transfer of information between two RAN nodes at any time via NG interface and the Core Network. An example of application is to exchange the RAN node's IP addresses in order to be able to use Xn interface between the NG-RAN node for Self-Optimised Networks (SON), as specified in TS 38.413.

5.26.1  Architecture Principles for Configuration Transfer  p. 361

Configuration Transfer between two RAN node provides a generic mechanism for the exchange of information between applications belonging to the RAN nodes.
In order to make the information transparent for the Core Network, the information is included in a transparent container that includes source and target RAN node addresses, which allows the Core Network nodes to route the messages. The mechanism is depicted in Figure 5.26.1-1.
Reproduction of 3GPP TS 23.501, Fig. 5.26.1-1: inter NG-RAN Configuration Transfer basic network architecture
Figure 5.26.1-1: inter NG-RAN Configuration Transfer basic network architecture
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The NG-RAN transparent containers are transferred from the source NG-RAN node to the destination NG-RAN node by use of Configuration Transfer messages.
A Configuration Transfer message is used from the NG-RAN node to the AMF over N2 interface, a AMF Configuration Transfer message is used from the AMF to the NG-RAN over N2 interface, and a Configuration Transfer Tunnel message is used to tunnel the transparent container from a source AMF to a target AMF over the N14 interface.
Each Configuration Transfer message carrying the transparent container is routed and relayed independently by the core network node(s).
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5.26.2  Addressing, routing and relaying  p. 362

5.26.2.1  Addressing  p. 362

All the Configuration Transfer messages contain the addresses of the source and destination RAN nodes. An NG-RAN node is addressed by the Target NG-RAN node identifier.

5.26.2.2  Routing  p. 362

The following description applies to all the Configuration Transfer messages used for the exchange of the transparent container.
The source RAN node sends a message to its core network node including the source and destination addresses. The AMF uses the destination address to route the message to the correct AMF via the N14 interface.
The AMF connected to the destination RAN node decides which RAN node to send the message to, based on the destination address.

5.26.2.3  Relaying  p. 362

The AMF performs relaying between N2 and N14 messages as described in TS 38.413, TS 29.518.

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