Content for  TS 23.503  Word version:  18.3.0

Network slice related policy control supports limitation of the data rate per network slice. A Maximum Slice Data Rate can be configured for an S-NSSAI (indicating the network slice subject to network slice data rate limitation control) by the operator (e.g. based on an SLA related to the network slice). The Maximum Slice Data Rate has an UL and a DL value. The Maximum Slice Data Rate defines the maximum allowed aggregate data rate across all GBR and Non-GBR QoS Flows within the network slice identified by an S-NSSAI. The PCF monitors the data rate of the network slice and ensures that it does not exceed the Maximum Slice Data Rate for that network slice by e.g. rejecting new SM Policy Associations, rejecting new GBR service data flows with high GBR requirements, changing the Authorized Session-AMBR values (if allowed by the HPLMN), changing the MBR values in PCC rules belonging to GBR service data flows or other actions depending on operator policies. When the PCF rejects the SM Policy Association Establishment procedure to the SMF due to the Maximum Slice Data Rate for that network slice is exceeded, then the SMF rejects the establishment of the PDU Session.

If the NWDAF is used for network slice data rate analysis, the PCF consumes the analytics from the NWDAF and receives the Data Volume Dispersion Analytics statistics outputs for all UEs of the network slice as defined in TS 23.288. The PCF subscribes to the NWDAF for periodic reporting when it becomes responsible for the first PDU Session of a slice (subject to limitation of data rate per network slice) and cancels the subscription when it stops to handle the last PDU Session of that slice. The NWDAF periodically provides the analytics output to the PCF. The PCF calculates the utilized data rate of the network slice by using the statistics output Data volume dispersed and Duration. When the utilized data rate of the network slice is getting close to or is exceeding the Maximum Slice Data Rate for this S-NSSAI obtained from the UDR, based on operator policy, the PCF may apply a policy decision to strengthen the traffic restrictions for individual PDU Sessions or PCC rules (see clause 6.1.4.1). When the utilized data rate of the network slice falls below the Maximum Slice Data Rate, the PCF may relax the traffic restrictions for individual PDU Sessions or PCC rules. When multiple PCFs for the same S-NSSAI are deployed, each PCF subscribes to the analytics from the NWDAF separately.

If the NWDAF is not deployed or is not to be used for network slice data rate analysis, the UDR maintains the Remaining Maximum Slice Data Rate per S-NSSAI and the PCF interacts with the UDR to deduct the value of the authorized Session-AMBR and the MBR of every GBR SDF from the Remaining Maximum Slice Data Rate per S-NSSAI for every PDU Session of this slice. When the remaining data rate for that S-NSSAI is close to zero, the PCF may, based on operator policies, apply a policy decision to strengthen the traffic restrictions for individual PDU Sessions or PCC rules (see clause 6.1.4.1). When the Remaining Maximum Slice Data Rate for that S-NSSAI increases again, the PCF may relax the traffic restrictions for individual PDU Sessions or PCC rules. The details on monitoring the data rate per network slice by the PCF are described in clause 6.2.1.10.

Based on operator policy, the PCF may, together with any other input for PCC decisions (see clause 6.2.1.2), make policy control decisions based on awareness of URSP rule enforcement for an application by using the following mechanisms:

• Policy control decisions based on awareness of URSP rule enforcement with UE assistance: PCF may make policy control decisions based on UE reported Connection Capabilities as illustrated in clause 6.1.6.2.
• Policy control decisions based on awareness of URSP rule enforcement without UE assistance: PCF may make policy control decisions without involving UE based on application detection as illustrated in clause 6.1.6.3.

The PCF for the UE may adjust the URSP rules when needed, based on the notified URSP rule enforcement information, which may include UE reported Connection Capabilities if available, PDU Session parameters if available, and detected application event if applicable. The PCF for the PDU Session may generate PCC rules under consideration of the traffic descriptor corresponding to the UE reported Connection Capabilities or the URSP rules which has been sent to the UE.

The PCF may obtain UE reporting of URSP rule enforcement as described in clause 6.6.2.4. Based on the received URSP rule enforcement information, the PCF for the PDU Session may interact with the PCF for the UE as described in clause 4.16.16 of TS 23.502. The PCF for the UE may adjust the URSP rules based on the notification from the PCF for a PDU Session e.g. when the PCF for the UE determines that the UE does not have up-to-date URSP rules.

The PCF for the UE may subscribe to Statistics for traffic monitoring of known traffic according to provisioned URSP rule(s). If the PCF for a UE is notified with traffic which is not expected according to a URSP rule as described in TS 23.288, the PCF for a UE may adjust the URSP rules when unexpected application traffic is detected. In detail, the PCF for a UE generate the input as described in clause 6.20.2 of TS 23.288 and the NWDAF notifies the unexpected traffic as described in clause 6.30.3 of TS 23.288. During the request of Analytics ID "PDU Session traffic analytics", the PCF for the UE includes the Traffic Descriptor of the URSP rules in the request of the analytic. The PCF sets Analytics Filter Information per Traffic Descriptor of the URSP rules as following:

• Area of Interest as the location of UEs where URSP rule enforcement is monitored;
• S-NSSAI corresponding to a Route Selection Descriptor of the URSP rule;
• DNN corresponding to a Route Selection Descriptor of the URSP rule.