5.21.3.2 NF Set and NF Service Set

Equivalent Control Plane NFs may be grouped into NF Sets, e.g. several SMF instances are grouped into an SMF Set. NFs within a NF Set are interchangeable because they share the same context data and may be deployed in different locations, e.g. different data centres.

In the case of SMF, multiple instances of SMFs within an SMF Set need to be connected to the same UPF:

• If the N4 association is established between a SMF instance and an UPF, each N4 association is only managed by the related SMF instance.
• If only one N4 association is established between a SMF Set and an UPF, any SMF in the SMF Set should be able to manage the N4 association with the UPF.

Furthermore, for a given UE and PDU Session any SMF in the SMF Set should be able to control the N4 session with the UPF (however, at any given time, only one SMF in the SMF Set will control the UPF for a given UE's PDU Session).

A Control Plane NF is composed of one or multiple NF Services. Within a NF a NF service may have multiple instances. These multiple NF Service instances can be grouped into NF Service Set if they are interchangeable with each other because they share the same context data.

NOTE: The actual mapping of instances to a given Set is up to deployment.