Section: 4.17.6 SMF Provisioning of available UPFs using the NRF 4.17.6.1 General
Content: This clause describes the provisioning of available UPFs in SMF using the NRF as documented in clause 6.3.3 of TS 23.501[ System architecture for the 5G System (5GS) ]  [2]. This optional node-level step takes place prior to selecting the UPF for PDU Sessions and may be followed by N4 Node Level procedures defined in clause 4.4.3 where the UPF and the SMF exchange information such as the support of optional functionalities and capabilities. As an option, UPF(s) may register in the NRF. This registration phase uses the Nnrf_NFManagement_NFRegister operation and hence does not use N4. For the purpose of SMF provisioning of available UPFs, the SMF uses the Nnrf_NFManagement_NFStatusSubscribe, Nnrf_NFManagement_NFStatusNotify and Nnrf_NFDiscovery services to learn about available UPFs. NOTE 1: The protocol used by UPF to interact with NRF is described in TS 29.510[ 5G System; Network function repository services; Stage 3 ]  [37] UPFs may be associated with UPF Provisioning Information in the NRF. The UPF Provisioning Information consists of: - a list of (S-NSSAI, DNN); - UE IPv4 Address Ranges and/or IPv6 Prefix Range(s) per (S-NSSAI, DNN); and NOTE 2: The above information can be used by the SMF for UPF selection when static IP address/prefix allocation is required for a UE. - a SMF Area Identity the UPF can serve. The SMF Area Identity allows limiting the SMF provisioning of UPF(s) using NRF to those UPF(s) associated with a certain SMF Area Identity. This can e.g. be used if an SMF is only allowed to control UPF(s) configured in NRF as belonging to a certain SMF Area Identity. - the supported ATSSS steering functionality, i.e. whether MPTCP functionality or ATSSS-LL functionality or MPQUIC functionality, or any combination of them is supported. - the supported UPF event exposure service and supported Event IDs, e.g. local notification of QoS Monitoring to AF or e.g. events for data collection to NWDAF by Nupf_EventExposure_Notify. The SMF Area Identity and UE IPv4 Address Ranges and/or IPv6 Prefix Range(s) are optional in the UPF Provisioning Information.