3GPP 23.501 v20.2.0 — the document's own text
5.6.12 Use of Network Instance
Taught in 12. The connection to a data network (The 5G system architecture, in depth), 5. The connection, and what is promised on it (The 5G system architecture, overview).
The SMF may provide a Network Instance to the UPF in FAR and/or PDR via N4 Session Establishment or N4 Modification procedures.
NOTE 1: a Network Instance can be defined e.g. to separate IP domains, e.g. when a UPF is connected to 5G-ANs in different IP domains, overlapping UE IP addresses assigned by multiple Data Networks, transport network isolation in the same PLMN, etc.
NOTE 2: As the SMF can provide over N2 the Network Instance it has selected for the N3 CN Tunnel Info, the 5G AN does not need to provide Network Instance to the 5GC.
The SMF determines the Network Instance based on local configuration.
The SMF may determine the Network Instance for N3 and N9 interfaces, taking into account e.g. UE location, registered PLMN ID of UE, S-NSSAI of the PDU Session.
The SMF may determine the Network Instance for N6 interface taking into account e.g. (DNN, S-NSSAI) of the PDU Session.
The SMF may determine the Network Instance for N19 interface taking into account e.g. the (DNN, S-NSSAI) identifying a 5G VN group.
NOTE 3: As an example, the UPF can use the Network Instance included in the FAR, together with other information such as Outer header creation (IP address part) and Destination interface in the FAR, to determine the interface in UPF (e.g. VPN or Layer 2 technology) for forwarding of the traffic.