Section: 4.4.3.1 N4 Association Setup Procedure
Content: The N4 Association Setup procedure is used to setup an N4 association between the SMF and the UPF, to enable the SMF to use the resources of the UPF subsequently to establish N4 Sessions. The SMF and UPF may exchange the supported functionalities on each side during these procedures. The setup of an N4 association is initiated by the SMF. SMF and UPF may additionally support an N4 association initiated by UPF. The SMF should only establish an N4 association with a UPF that supports F-TEID allocation at the UPF. The SMF initiates the N4 Association Setup procedure to request to setup an N4 association towards a UPF prior to establishing a first N4 session on this UPF. When receiving an N4 Association Setup Request, the UPF shall send an N4 Association Setup Response. N4 Association Setup procedure can be used to request the UPF to measure and report the clock drift between the external time and 5GS time for one or more external time domains by provisioning External Clock Drift Report and providing the corresponding Time Domain number(s) as specified in TS 29.244[ Interface between the Control Plane and the User Plane nodes ]  [69]. The SMF may omit the Time domain number in the request; in this case the UPF shall report the clock drift for all Time domains the UPF is connected to. Figure 4.4.3.1-1: N4 association setup procedure initiated by SMF The UPF may initiate the N4 Association Setup procedure to request to setup an N4 association towards a SMF prior to establishing a first N4 session on this UPF. When receiving an N4 Association Setup Request, the SMF shall send an N4 Association Setup Response. Figure 4.4.3.1-2: N4 association setup procedure initiated by UPF