Section: 6.3.24 TSCTSF Discovery
Content: The NFs (e.g. NEF, AF and PCF) may utilize the NRF to discover TSCTSF instance(s) unless TSCTSF information is available by other means, e.g. locally configured in the requested NF. The following factors may be considered for TSCTSF discovery and selection: - DNN and S-NSSAI. When the NF discovers the TSCTSF for a DNN/S-NSSAI, the NRF provides the NF with NF profile(s) of TSCTSF instance(s) belonging to single TSCTSF Set for a given DNN/S-NSSAI. For example, the same TSCTSF Set shall be selected by the PCF serving PDU Sessions for this DNN and S-NSSAI to notify the TSCTSF for a PDU Session that is potentially impacted by the (g)PTP time synchronization service. - GPSI or External Group Identifier. TSCTSF NF consumers (which manage network signalling not based on SUPI/SUCI (e.g. the NEF)) select a TSCTSF instance based on the GPSI or External Group ID range the UE's GPSI or External Group ID belongs to or based on the results of a discovery procedure with NRF using the UE's GPSI or External Group ID as input for TSCTSF discovery. - SUPI or Internal Group ID. TSCTSF NF consumers select a TSCTSF 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 or Internal Group ID as input for TSCTSF discovery. If the TSCTSF is locally configured in NFs, it shall be ensured that the same TSCTSF Set is configured in all NFs (e.g. NEF, AF and PCF) for the given DNN and S-NSSAI. NOTE: Thus, it is assumed that there is only one TSCTSF Set for a given DNN/S-NSSAI in this Release of the specification.