Content for  TS 23.503  Word version:  18.5.0

The session management related policy control functionality of the Policy and Charging control framework for the 5G system provides the functions for policy and charging control as well as event reporting for service data flows. The PCF evaluates operator policies that are triggered by events received from the AF directly or indirectly via an NEF, from the SMF, from the AMF and from the CHF as well as changes in User subscription Profile. The following clauses describe the most relevant session management related functionality in detail.

Reporting refers to the differentiated PDU Session resource usage information (measured at the UPF) being reported by the SMF to the CHF. The SMF shall report usage information for online and offline charging. The SMF shall report usage information for each charging key value. For service data flow charging, for the case of sponsored data connectivity, the reports for offline charging shall report usage for each charging key, Sponsor Identity and Application Service Provider Identity combination if Sponsor Identity and Application Service Provider Identifier have been provided in the PCC rules. The SMF shall report usage information for each charging key/service identifier combination if service identifier level reporting is requested in the PCC rule. Charging information shall be reported based on the result from the service data flow detection and measurement on a per PDU Session basis. A report may contain multiple containers, each container associated with a charging key, charging key and Sponsor Identity (in the case of sponsored connectivity) or charging key/service identifier.

The credit management applies only for service data flow with online charging method and shall operate on a per charging key basis. The SMF should initiate one charging session with the CHF for each PDU Session subject to charging, in order to perform credit management within the charging session. The SMF shall request a credit for each charging key occurring in a PCC rule. It shall be up to operator configuration whether the SMF shall request credit in conjunction with the PCC rule being activated or when the first packet corresponding to the service is detected. The CHF may either grant or deny the request for credit. The CHF shall strictly control the rating decisions. During PDU Session establishment and modification, the SMF shall request credit using the information after applying policy enforcement action (e.g. upgraded or downgraded QoS information), if applicable, even though the SMF has not signalled this information to the AMF or RAN. The events trigger information which may be received from the CHF, causing the SMF to perform a usage reporting and credit request to CHF when the event occurs are specified in TS 32.255. The CHF may subscribe to Change of UE presence in Presence Reporting Area at any time during the life time of the charging session as described in TS 32.255. If the PCF set the Out of credit event trigger (see clause 6.1.3.5), the SMF shall inform the PCF about the PCC rules for which credit is no longer available together with the applied termination action.

The Policy Control Request Triggers relevant for SMF define the conditions when the SMF shall interact again with PCF after a PDU Session establishment as defined in the Session Management Policy Establishment and Session Management Policy Modification procedure as defined in TS 23.502. The PCR triggers are not applicable any longer at termination of the SM Policy Association. The access independent Policy Control Request Triggers relevant for SMF are listed in Table 6.1.3.5-1. The differences with Table 6.2 and Table A.4.3-2 in TS 23.203 are shown, either "none" means that the parameter applies in 5GS or "removed" meaning that the parameter does not apply in 5GS, this is due to the lack of support in the 5GS for this feature or "modified" meaning that the parameter applies with some modifications defined in the parameter.

When the EPS Fallback trigger is armed by the PCF, the SMF shall report the event to the PCF when a QoS Flow with 5QI=1 is rejected due to EPS Fallback. When the Location change trigger is armed, the SMF shall subscribe to the AMF for reports on changes in location to the level indicated by the trigger. If credit-authorization triggers and Policy Control Request Triggers require different levels of reporting of location change for a single UE, the location to be reported should be changed to the highest level of detail required. However, there should be no request being triggered for PCC rules update to the PCF if the report received is more detailed than requested by the PCF. The Resource modification request trigger shall trigger the PCF interaction for all resource modification requests not tied to a specific QoS Flow received by SMF. The resource modification request received by SMF may include request for guaranteed bit rate changes for a traffic aggregate and/or the association/disassociation of the traffic aggregate with a 5QI and/or a modification of the traffic aggregate. The enforced PCC rule request trigger shall trigger a SMF interaction to request PCC rules from the PCF for an established PDU Session. This SMF interaction shall take place within the Revalidation time limit set by the PCF in the PDU Session related policy information. The SMF reports that the enforced PCC rule request trigger was met and the enforced PCC Rules. The UE IP address change trigger shall trigger a SMF interaction with the PCF if a UE IP address is allocated or released during the lifetime of the PDU Session. The SMF reports that the UE IP address change trigger was met and the new or released UE IP address. The UE MAC address change trigger shall trigger a SMF interaction with the PCF if a new UE MAC address is detected or a used UE MAC address is inactive for a specific period during the lifetime of the Ethernet type PDU Session. The SMF reports that the UE MAC address change trigger was met and the new or released UE MAC address. The Access Network Charging Correlation Information trigger shall trigger the SMF to report the assigned access network charging identifier for the PCC rules that are accompanied with a request for this trigger at activation. The SMF reports that the Access Network Charging Correlation Information trigger was met and the Access Network Charging Correlation Information. If the Usage report trigger is set and the volume or the time thresholds, earlier provided by the PCF, are reached, the SMF shall report this situation to the PCF. If both volume and time thresholds were provided and the thresholds, for one of the measurements, are reached, the SMF shall report this situation to the PCF and the accumulated usage since last report shall be reported for both measurements. The management of the Presence Reporting Area (PRA) functionality enables the PCF to subscribe to reporting change of UE presence in a particular Presence Reporting Area. Upon every interaction with the SMF, the PCF may activate / deactivate reporting changes of UE presence in Presence Reporting Area by setting / unsetting the corresponding trigger by providing the PRA Identifier(s) and additionally the list(s) of elements comprising the Presence Reporting Area for UE-dedicated Presence Reporting Area(s). The SMF shall subscribe to the UE Location Change notification from the AMF by providing an area of interest containing the PRA Identifier(s) and additionally the list(s) of elements provided by the PCF as specified in clause 5.6.11 of TS 23.501 and in clause 5.2.2.3.1 of TS 23.502. When the Change of UE presence in Presence Reporting Area trigger is armed, i.e. when the PCF subscribes to reporting change of UE presence in a particular Presence Reporting Area and the reporting change of UE presence in this Presence Reporting Area was not activated before, the SMF subscribes to the UE mobility event notification service provided by the AMF for reporting of UE presence in Area of Interest which reports when the UE enters or leaves a Presence Reporting Area (an initial report is received when the PDU Session specific procedure is activated). The SMF reports the PRA Identifier(s) and indication(s) whether the UE is inside or outside the Presence Reporting Area(s), and indication(s) if the corresponding Presence Reporting Area(s) is set to inactive by the AMF to the PCF. When PCF modifies the list of PRA id(s) to change of UE presence in Presence Reporting Area for a particular Presence Reporting Area(s), the SMF removes or adds the PRA id(s) provided in the UE mobility event notification service provided by AMF for reporting of UE presence in Area Of Interest. When the PCF unsubscribes to reporting change of UE presence in Presence reporting Area, the SMF unsubscribes to the UE mobility event notification service provided by AMF for reporting of UE presence in Area Of Interest, unless subscriptions to AMF remains due to other triggers. The SMF stores PCF subscription to reporting for changes of UE presence in Presence Reporting Area and notifies the PCF with the PRA Identifier(s) and indication(s) whether the UE is inside or outside the Presence Reporting Area(s) based on UE location change notification in area of interest received from the serving node according to the corresponding subscription. If PCF is configured with a PRA identifier referring to the list of PRA Identifier(s) within a Set of Core Network predefined Presence Reporting Areas as defined in TS 23.501, it activates the reporting of UE entering/leaving each individual PRA in the Set of Core Network predefined Presence Reporting Areas, without providing the complete set of individual PRAs. When a PRA set identified by a PRA Identifier was subscribed to report changes of UE presence in Presence Reporting Area by the PCF, the SMF additionally receives the PRA Identifier of the PRA set from the AMF, along with the individual PRA Identifier(s) belonging to the PRA set and indication(s) of whether the UE is inside or outside the individual Presence Reporting Area(s), as described in TS 23.501. When the Out of credit detection trigger is set, the SMF shall inform the PCF about the PCC rules for which credit is no longer available together with the applied termination action. When the Reallocation of credit detection trigger is set, the SMF shall inform the PCF about the PCC rules for which credit has been reallocated after credit was no longer available and the termination action was applied. The Start of application traffic detection and Stop of application traffic detection triggers shall trigger an interaction with PCF once the requested application traffic is detected (i.e. Start of application traffic detection) or the end of the requested application traffic is detected (i.e. Stop of application traffic detection) unless it is requested within a specific PCC Rule to mute such interaction for solicited application reporting or unconditionally in the case of unsolicited application reporting. The application identifier and service data flow descriptions, if deducible, shall also be included in the report. An application instance identifier shall be included in the report both for Start and for Stop of application traffic detection when service data flow descriptions are deducible. This is done to unambiguously match the Start and the Stop events. At PCC rule activation, modification and deactivation the SMF shall send, as specified in the PCC rule, the User Location Report and/or UE Timezone Report to the PCF. If the trigger for Access Network Information reporting is set, the SMF shall check the need for access network information reporting after successful installation/modification or removal of a PCC rule or upon termination of the PDU Session. The SMF shall check the Access Network Information report parameters (User Location Report, UE Timezone Report) of the PCC rules and report the access network information to the PCF. The SMF shall not report any subsequent access network information updates received from the PDU Session without any previous updates of related PCC rule unless the associated QoS Flow or PDU Session has been released. If the SMF receives a request to install/modify or remove a PCC rule with Access Network Information report parameters (User Location Report, UE Timezone Report) set the SMF shall initiate a PDU Session modification to retrieve the current access network information of the UE and forward it to the PCF afterwards. If the Access Network Information report parameter for the User Location Report is set and the user location (e.g. cell) is not available to the SMF, the SMF shall provide the serving PLMN identifier to the PCF. The Credit management session failure trigger shall trigger a SMF interaction with the PCF to inform about a credit management session failure and to indicate the failure reason, and the affected PCC rules. The default QoS change triggers shall trigger the PCF interaction for all changes in the default QoS data received in SMF from the UDM. The Session AMBR change trigger shall trigger the SMF to provide the Session-AMBR to the PCF containing the DN authorised Session AMBR if received from the DN-AAA, or the Subscribed Session-AMBR received from the UDM as described in clause 5.6.6 of TS 23.501. The default QoS change trigger reports a change in the default 5QI/ARP retrieved by SMF from UDM, as explained in clause 5.7.2.7 of TS 23.501. If the PCC Rules bound to a QoS Flow are removed when the corresponding QoS Flow is removed or the PCC rules are failed to be enforced, the SMF shall report this situation to the PCF and may provide the reason for failure, if the reason for failure is that the UE is temporarily unreachable, the SMF may also provide the maximum waiting time to the PCF, in this case the PCF does not provide the same or updated PCC Rules for the established PDU Session before the maximum waiting time expires, the PCF may also subscribe to PCRT on change of UE reachability. In other failure scenarios, the PCF may then provide the same or updated PCC rules for the established PDU Session. If the trigger for successful resource allocation is set and the PCF has also provided an indication that a specific PCC rule is subject to this trigger, the SMF shall report to the PCF when the resources associated to this PCC rule have been successfully allocated. The SMF shall report resource allocation failure always to the PCF, independently of this trigger. If the SMF reports resource allocation failure for a PCC rule containing MA PDU Session Control information with Redundant as Steering Mode (see clause 5.32.4 of TS 23.501), the SMF shall also indicate the respective Access Type. If the GFBR of the QoS Flow can no longer (or can again) be guaranteed trigger is armed, the SMF shall check the need for reporting to the PCF when the SMF receives an explicit notification from (R)AN indicating that GFBR of the QoS Flow can no longer (or can again) be guaranteed or when the condition described in clause 5.7.2.4 of TS 23.501 is met during the handover. The SMF shall report that GFBR of the QoS Flow can no longer (or can again) be guaranteed accordingly to the PCF for those PCC rules which are bound to the affected QoS Flow and have the QoS Notification Control (QNC) parameter set. If additional information is received with the notification from NG-RAN (see clause 5.7.2.4 of TS 23.501), the SMF shall also provide to the PCF the reference to the Alternative QoS parameter set corresponding to the Alternative QoS Profile referenced by NG-RAN. If NG-RAN has indicated that the lowest priority Alternative QoS Profile cannot be fulfilled, the SMF shall indicate to the PCF that the lowest priority Alternative QoS parameter set cannot be fulfilled. In an interworking scenario between 5GS and EPC/E-UTRAN, as explained in clause 4.3 of TS 23.501, the PCF may subscribe via the SMF also to the Policy Control Request Triggers described in clause 6.1.2.5 when the UE is served by the EPC/E-UTRAN. The change of DN Authorization Profile Index shall trigger a SMF interaction to send DN Authorization Profile Index to retrieve a list of PCC Rules (as defined in clause 6.3) and/or PDU Session related policy (as defined in clause 6.4) for an established PDU Session. If the trigger for 5GS Bridge/Router information available is armed, the SMF shall report the 5GS Bridge/Router information when the SMF has determined or updated the 5GS Bridge/Router information, e.g. when SMF has detected an Ethernet port which supports exchange of Ethernet Port Management Information Containers or received User plane node Management Information Container or Port Management Information Container. If a new manageable Ethernet DS-TT port is detected, the SMF provides User plane node ID, the port number and optionally MAC address of the related port of the related PDU Session to the PCF. If the SMF has received UE-DS-TT Residence Time then the SMF also provides UE-DS-TT Residence Time to the PCF. If the SMF has received the User plane node Management Information Container from NW-TT or Port Management Information Container from NW-TT or DS-TT, the SMF also provides User plane node Management Information Container or Port Management Information Container and related port number to the PCF. In the case of Deterministic Networking, the SMF may also provide the MTU size for IPv4 or the MTU size for IPv6. When the QoS Monitoring trigger is set, the SMF shall, upon receiving the QoS Monitoring report from the UPF, send the measurement report to the PCF. If the Policy Control Request Trigger "DDN Failure event subscription with Traffic Descriptor" or "DDD Status event subscription with Traffic Descriptor" is set, the SMF shall request policies if it received a subscription or cancellation of notifications for availability after DDN Failure event with traffic descriptor or DDD Status event with traffic descriptor, respectively. The SMF indicates whether it is a subscription or cancellation event and provides the received Traffic Descriptor as well as the requested type(s) of notifications (notifications about downlink packets being buffered, and/or discarded) to the PCF. When the SMF indicates a subscription event, the PCF checks whether an installed PCC rule exists for the received Traffic Descriptor and if so, the PCF sets the Downlink Data Notification Control information of that PCC rule according to the requested type(s) of notifications. Otherwise, the PCF provides a new PCC Rule with the received Traffic Descriptor in the SDF Template, the Downlink Data Notification Control information set according to the requested type(s) of notifications and other PCC Rule information set to the same values as in the existing PCC rule that previously matched the traffic. When the new PCC has to be bound to the QoS Flow associated with the default QoS rules, the PCF sets the "Bind to QoS Flow associated with the default QoS rule" parameter. From now on, the PCF needs to keep the PCC rule for the DDD event detection fully synchronized with the existing PCC rule that previously matched the traffic for all other policy and charging control settings to ensure the same user experience and traffic treatment according to the operator policy. When the SMF indicates a cancellation event, the PCF removes the Downlink Data Notification Control information in the installed PCC Rule or removes the PCC Rule if a new PCC rule has been provided during the subscription event and this PCC rule is no longer necessary for any other policy enforcement. The QoS constraints change trigger shall trigger a SMF interaction with the PCF if QoS constraints are received by the SMF during the lifetime of the PDU Session. The SMF reports that the QoS constraints change trigger was met and the new QoS constraints. When the Satellite backhaul category change trigger is armed, the SMF reports to the PCF that the Satellite backhaul category change was met and the new Satellite backhaul category (including satellite backhaul is no longer used) when it becomes aware that there is a change of the backhaul which is used for the PDU Session between different types of satellite backhaul, or between satellite backhaul and a non-satellite backhaul. The SMF determines whether or not a satellite backhaul is used and whether there is a change of backhaul based on signalling from the AMF as specified in TS 23.501. The NWDAF info change trigger shall trigger the SMF to interact with the PCF when the list of NWDAF Instance IDs used for the PDU Session or associated Analytics IDs used for the PDU Session are changed in the SMF. The Request for reporting the PCF binding information indicates to the SMF to report to the PCF for the PDU Session that the trigger was met and the updated PCF binding information of the PCF for the UE received from the AMF. When the Notification on BAT offset trigger is set, the SMF shall, upon receiving a BAT offset and optionally an adjusted periodicity from the RAN (in a notification that GFBR of the QoS Flow can no longer be guaranteed as defined in clause 5.27.2.5.3 of TS 23.501), report the BAT offset and optionally the adjusted periodicity to the PCF for the PCC rule which is bound to the QoS Flow for which the notification from RAN was received. The UE reporting Connection Capabilities from associated URSP rule trigger indicates to the SMF that when a UE includes Connection Capabilities in the PDU Session Establishment Request or PDU Modification Request, the SMF shall forward this information to the PCF as described in clause 6.6.2.4, if the PCRT is set in the SMF. The UE Policy Container received or delivery failure for UE Policy Container delivery via EPS trigger shall trigger a SMF interaction with the PCF, if a UE Policy Container is received from the UE via EPS or in case of a delivery failure for UE Policy Container delivery via EPS (with appropriate reason, e.g. UE is not reachable), as described in clause 4.11.0a.2a.10 of TS 23.502. When the Change of HR-SBO support indication trigger is armed, the H-SMF reports to the H-PCF that the HR-SBO support indication change was met. The H-SMF determines whether there is a change of HR-SBO support indication based on HR-SBO Request Indication from the V-SMF and/or the SM subscription data from UDM as described in clause 6.7.2.2 of TS 23.548. The Network Slice Replacement trigger shall trigger a SMF interaction with the PCF to notify change between S-NSSAI and Alternative S-NSSAI when the SMF determines that the existing PDU Session and existing SM Policy Association can be retained as described in clause 4.15.19 of TS 23.501. The SMF provides Alternative S-NSSAI if the PDU Session is transferred from a S-NSSAI to its Alternative S-NSSAI. The SMF indicates to the PCF that the PDU Session is transferred from the Alternative S-NSSAI to the replaced S-NSSAI, when the replaced S-NSSAI is available again and the PDU Session is transferred to the replaced S-NSSAI. If the 'ECN marking for L4S can no longer (or can again) be performed trigger' is armed, the SMF shall report to the PCF for those PCC rules which have enabled ECN marking for L4S (explicitly or implicitly as described in clause 6.1.3.22) if neither RAN nor UPF PSA ECN marking for L4S can be enabled on the affected QoS Flows, and when ECN marking for L4S can be enabled on the affected QoS Flows (again). When the UE reachability status change is armed, the SMF subscribes to event of "UE reachability status" by using the Namf_EventExposure_Subscribe defined in clause 5.2.2.3.1 of TS 23.502. The SMF reports a change of the UE reachability status to the PCF.