Content for  TS 23.503  Word version:  18.1.0

The PCF provides the following session management related functionality:

• Policy and charging control for a service data flows;
• PDU Session related policy control;
• PDU Session event reporting to the AF.

The PCF provides authorized QoS for a service data flow and other network control regarding service data flow detection, gating, QoS and charging (except credit management) towards the SMF. The PCF uses the service information received from the AF (e.g. SDP information or other available application information) and/or the subscription information received from the UDR to calculate the proper QoS authorization (QoS class identifier, bitrates). The PCF may also take into account the requested QoS received from the SMF and the analytics information (e.g. analytics related to "Service Experience") received from the NWDAF. The PCF may check that the service information provided by the AF is consistent with both the operator defined policies and the related subscription information as received from the UDR during PDU Session establishment before storing the service information. The PCF may reject the request received from the AF when the service information is not consistent with either the related subscription information or the operator defined policies and may indicate, in the response to the AF, the service information that can be accepted by the PCF (e.g. the acceptable bandwidth). In the absence of other policy control mechanisms outside the scope of PCC, it is recommended that the PCF include this information in the response. In this Release, the PCF supports only the interaction with a single AF for each AF session. The Authorization of QoS shall be based on complete service information unless the PCF is required to perform the authorization of QoS based on preliminary service information. The PCF shall after receiving the complete service information, update the affected PCC rules accordingly. At reception of the service information from the AF if configured through policy and taking into account information defined in TS 26.114, the PCF determines the Maximum Packet Loss Rate for UL and DL based on the service information and sends it to SMF along with the PCC rule. The PCF supports usage monitoring control as described in clause 6.2.1.7. The PCF supports sponsored data connectivity for a service as described in clause 6.2.1.8. The PCF uses the information relating to subscriber spending available in the CHF as input for policy decisions related to e.g. QoS control, gating or charging conditions. Details for policy decisions based on spending limits are described in clause 6.1.3.17. The PCF uses one or more pieces of information defined in the clause 6.2.1.2 as input for the selection of traffic steering policies used to control the steering of the subscriber's traffic as described in clause 6.1.3.14. The PCF reports PDU Session events, e.g. Access Type, RAT Type (if applicable), Access Network Information, PLMN identifier where the UE is located, as described in clause 6.1.3.18. The subscription and reporting of events when the target for reporting is an Internal Group Identifier or any UE accessing a combination of (DNN, S-NSSAI), is described in clause 5.2.5.7 of TS 23.502. The events that can be reported by the PCF are described in clause 6.1.3.18. The subscription and reporting of events targeting an individual UE IP address (IPv4 address or IPv6 prefix) and optionally the DN information are described below. The events that can be reported by the PCF are described in clause 6.1.3.18. The PCF shall ensure that the sum of the packet filters used by all PCC rules which trigger the generation of signalled QoS rules does not exceed the number of supported packet filters for signalled QoS rules indicated by the UE for the PDU Session, if this information is provided by the SMF (as defined in clause 6.2.1.2). For EPC IWK, when PCF receives from the SMF of the report on UE resumed from suspend state, the PCF may provision PCC Rules to the SMF to trigger an IP-CAN Session modification procedure. The PCF may provide the IP index as the PDU Session related policy to the SMF for IP address/Prefix allocation at SM Policy Association Establishment. If PCF receives from the SMF an allocated IP address/Prefix for the PDU Session, it shall not include IP Index into the PDU Session related policy. On receiving the DN Authorization Profile Index provided by the SMF at the establishment or modification of the SM Policy Association for a PDU Session, the PCF takes the DN Authorization Profile Index as input for a policy decision and then obtains the list of PCC Rules (as defined in clause 6.3) and/or PDU Session related policy (as defined in clause 6.4) and provides them to the SMF as part of the Session Management Policy Control Data for enforcement. On receiving the Session-AMBR provided by the SMF at the establishment or modification of the SM Policy Association for a PDU Session under the conditions defined in clause 5.6.6 of TS 23.501, the PCF provides the Authorized Session-AMBR as part of the PDU Session policy control information defined in clause 6.4. The PCF provides DNAI(s) in the PCC rule(s) to the SMF, taking into account the AF request and the Local routing indication from the PDU Session policy control subscription information. When the PCF detects that all PCC rules related to an AF session are removed, or the PCF detects that the SM Policy Association is terminated, the PCF shall request the AF to terminate the AF session. If the SMF indicated that the PCC rules were removed or that the SM Policy Association is terminated due to PS to CS handover, the PCF shall indicate PS to CS handover as cause within the request to terminate the AF session.

The PCF provides the following non-session management related functionality:

• Access and mobility related policy control (as described in clause 6.1.2.1);
• UE policy information control (as described in clause 6.1.2.2);
• Negotiation for future BDT (as described in clause 6.1.2.4);
• Negotiation for planned transfer with QoS requirements (as described in clause 6.1.2.7).

The PCF provides the following network slice related functionality:

• Limitation of the data rate per network slice (as described in clause 6.1.4).

The PCF supports monitoring and limitation of the data rate per S-NSSAI. If the S-NSSAI is subject to network slice data rate limitation the Remaining Maximum Slice Data rate per S-NSSAI is stored in the UDR as Data Set "Policy Data" and Data Subset "Network Slice Specific Policy Control Data" as defined in clause 6.2.1.3. The PCF interacts with the UDR to update the network slice specific policy control information per S-NSSAI in the UDR, i.e. the Remaining Maximum Slice Data Rate per S-NSSAI, so that the usage of multiple PCFs for the same S-NSSAI is enabled.

For the purpose of monitoring the data rate per S-NSSAI, the PCF shall perform the following for an SM Policy Association with an S-NSSAI subject to data rate limitation:

• At the establishment of a SM Policy Association, the PCF shall check whether the Remaining Maximum Slice Data Rate is higher than the Authorized Session-AMBR. If so, the PCF shall deduct the value of the Authorized Session-AMBR allocated to the PDU Session from the Remaining Maximum Slice Data Rate for that S-NSSAI in the UDR. If the Remaining Maximum Slice Data Rate is not sufficient, the PCF shall reject the establishment of the SM Policy Association.
• At the time a PCC Rule of a GBR service data flow is installed, modified or activated in the SMF, the PCF requests reporting "Successful resource allocation" with the corresponding Policy Control Request Trigger. When the SMF reports that the resources are successfully allocated, the PCF shall deduct the value of the MBR authorized for the GBR service data flow from the Remaining Maximum Slice Data Rate for that S-NSSAI in the UDR.
• At the time a change of Authorized Session-AMBR occurs or a PCC Rule containing a GBR value is removed or modified, the PCF shall update the Remaining Maximum Slice Data Rate for that S-NSSAI in the UDR accordingly.
• If the Remaining Maximum Slice Data Rate for that S-NSSAI reaches a (operator defined) threshold that indicates that it is closer to zero, 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) and interact with the SMF accordingly. 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.
• At the time the SM Policy Association for an S-NSSAI subject to data rate limitation is terminated, the PCF shall add the value of the Authorized Session-AMBR allocated to the PDU Session to the Remaining Maximum Slice Data Rate for that S-NSSAI in the UDR.

The PCF supports monitoring and limitation of the data rate per group. If the group is subject to data rate limitation the Group MBR for the group is stored in the UDR as defined in clause 5.29.2 of TS 23.501. The PCF interacts with the UDR to update the Group MBR specific policy control information per group in the UDR, i.e. the Remaining Group MBR per group, so that the usage of multiple PCFs for the same group is enabled.

For the purpose of monitoring the data rate per group, the PCF shall perform the same operations as Slice-MBR described in clause 6.2.1.10.2 with the following mapping:

• Instead of handling Maximum Slice Data Rate per S-NSSAI, the UDR and PCF handles the Maximum Group MBR per group identified by DNN and S-NSSAI.
• Instead of deducting the value of the authorized Session-AMBR and the MBR of every GBR SDF for every PDU Session of a slice, the PCR deducts such value for every PDU Session accessing to the group.