Section: 6.3.11 CHF discovery and selection
Content: The CHF discovery and selection function is supported by the SMF, the AMF, the SMSF and the PCF. It is used by the SMF to select a CHF that manages the online charging or offline charging for a PDU Session of a subscriber. It is used by the AMF to select a CHF that manages the online charging or offline charging for 5G connection and mobility of a subscriber. It is used by the SMSF to select a CHF that manages the online charging or offline charging for the SMS over NAS transactions of a subscriber. It is used by the PCF to select a CHF that manages the spending limits for a subscriber and/or a PDU Session of a subscriber. For the PCF to select the CHF, the address(es) of the CHF, including the Primary CHF address and the Secondary CHF address, may be: - stored in the UDR as part of the PDU Session policy control subscription information as defined in clause 6.2.1.3 of TS 23.503[ Policy and charging control framework for the 5G System (5GS); Stage 2 ]  [45]. - stored in the UDR as part of the UE context policy control subscription information as defined in clause 6.2.1.3 of TS 23.503[ Policy and charging control framework for the 5G System (5GS); Stage 2 ]  [45]. - stored in the UDR as part of the Access and Mobility policy control subscription information as defined in clause 6.2.1.3 of TS 23.503[ Policy and charging control framework for the 5G System (5GS); Stage 2 ]  [45]. - locally configured in the PCF based on operator policies. - discovered using NRF as described in in clause 6.1 of TS 32.290[ Telecommunication management; Charging management; 5G system; Services, operations and procedures of charging using Service Based Interface (SBI) ]  [67]. NOTE 1: The operator can perform the above UDR provisioning or local configuration in a consistent manner such that the same CHF address is used for SM policy, AM policy and UE policy. If NRF discovery is used, it is up to the PCF logic (or SCP logic when working in Delegated Discovery mode) and operator configuration to guarantee the CHF address consistency. The address(es) of the CHF shall be applicable for all services provided by the CHF. The CHF address(es) that a stored in the UDR or configured in the PCF may be complemented by the associated CHF instance ID(s) and CHF set ID(s) (see clause 6.3.1.0) stored or configured in the same location. The CHF address(es) retrieved from the UDR and possible associated CHF instance ID(s) and CHF set ID(s) take precendence over the locally configured CHF address(es) and possible associated CHF instance ID(s) and CHF set ID(s), and over the CHF address(es) discoverred by the NRF. If no CHF address(es) is received from the UDR, the PCF selects, based on operator policies, either the CHF addresse(es) provided by NRF, or the locally configured CHF address(es) and possible associated CHF instance ID(s) and CHF set ID(s). If the PCF has a CHF set ID but no CHF instance ID associated to the CHF address(es) in the same location, the CHF instance within the CHF set may change. If the PCF is not able to reach the CHF address(es), it should query the NRF for other CHF instances within the CHF set. If the PCF received a CHF set ID and a CHF instance ID associated to the CHF address(es) in the same location, the CHF service instance within the CHF may change. If an PCF is not able to reach the CHF address(es), it should query the NRF for other CHF service instances within the CHF. To enable the SMF to select the same CHF that is selected by the PCF for a PDU Session, the PCF provides the selected CHF address(es) and, if available, the associated CHF instance ID(s) and/or CHF set ID(s) in the PDU Session related policy information to the SMF as described in Table 6.4-1 of TS 23.503[ Policy and charging control framework for the 5G System (5GS); Stage 2 ]  [45] and the SMF applies the CHF address and if available, the associated CHF instance ID(s) and/or CHF set ID(s) passed from the PCF as defined in clause 5.1.8 of TS 32.255[ Telecommunication management; Charging management; 5G data connectivity domain charging; Stage 2 ]  [68]. Otherwise, the SMF selection of the CHF as defined in clause 5.1.8 of TS 32.255[ Telecommunication management; Charging management; 5G data connectivity domain charging; Stage 2 ]  [68] applies. If operator policies indicates the AMF should select the same CHF that is selected by the PCF for a UE, the PCF provides the selected CHF address(es) and, if available, the associated CHF instance ID(s) and/or CHF set ID(s) in the Access and mobility related policy information to the AMF as described in Table 6.5-1 of TS 23.503[ Policy and charging control framework for the 5G System (5GS); Stage 2 ]  [45] and the AMF may apply the CHF address and, if available, the associated CHF instance ID(s) and/or CHF set ID(s) passed from the PCF as defined in clause 5.1.3 of TS 32.256[ Charging management; 5G connection and mobility domain charging; Stage 2 ]  [114]. Otherwise, the AMF selection of the CHF as defined in clause 5.1.3 of TS 32.256[ Charging management; 5G connection and mobility domain charging; Stage 2 ]  [114] applies. How the CHF is selected by the SMSF is defined in clause 5.4 of TS 32.274[ Telecommunication management; Charging management; Short Message Service (SMS) charging ]  [118]. If the NF consumer performs discovery and selection via NRF, the CHF selection function in NF consumers selects a CHF instance based on the available CHF instances obtained from the NRF. The CHF selection functionality in NF consumer or in SCP should consider one of the following factors: 1. CHF Group ID of the UE's SUPI. NOTE 2: The NF Consumer can infer the CHF Group ID the UE's SUPI belongs to, based on the results of CHF discovery procedures with NRF. 2. SUPI; the NF consumer selects a CHF instance based on the SUPI range the UE's SUPI belongs to or based on the results of a discovery procedure with NRF using the UE's SUPI as input for CHF discovery. In the case of delegated discovery and selection in SCP, the NF consumer shall include all available factors in the request towards SCP.