5.29.4 User Plane handling

User Plane management as defined for 5GS in clause 5.8 is applicable to 5G LAN-type services with the following clarifications:

• There are three types of traffic forwarding methods allowed for 5G VN communication:
• N6-based, where the UL/DL traffic for the 5G VN communication is forwarded to/from the DN;

NOTE 1: Optionally a L2TP tunnel can be established over N6 as described in clause 5.8.2.16.

• N19-based, where the UL/DL traffic for the 5G VN group communication is forwarded between PSA UPFs of different PDU sessions via N19. N19 is based on a shared User Plane tunnel connecting PSA UPFs of a single 5G VN group.
• Local switch, where traffic is locally forwarded by a single UPF if this UPF is the common PSA UPF of different PDU Sessions for the same 5G VN group.
• For UPFs served by a single SMF Set, the SMF instance(s) in the SMF set handles the user plane paths of the 5G VN group, including:
• The SMF instance(s) may prefer to select a single PSA UPF for as many PDU sessions (targeting the same 5G VN group) as possible, in order to implement local switch on the UPF.
• (if needed) Establishing N19 tunnels between PSA UPFs served by the same SMF set to support N19-based traffic forwarding.
• If multiple SMF (Set)s are serving a 5G VN, user plane forwarding between UPFs served by different SMF (Set)s can be achieved via the DN (i.e. N6) or via user plane tunnels on N6/N19 as described in clause 5.29.3.

NOTE 2: The above user plane tunnels may be using GTP-U or IETF VPN. For example, for IP-type traffic, the traffic routing can be based on routing protocols or pre-configured IP address ranges/prefixes corresponding different SMF sets; for ethernet-type traffic, the traffic routing can be based on the learned MAC address over the user plane tunnels between UPFs controlled by different SMF sets, etc. How to implement such user plane tunnels configured between these UPFs is up to network implementation and deployment.

• For Ethernet PDU Session, the SMF may instruct the UPF(s) to classify frames based on VLAN tags and to add and remove VLAN tags, on frames received and sent on N6 or N19 or internal interface ("5G VN internal"), as described in clause 5.6.10.2.

NOTE 3: For handling VLAN tags for traffic on N6, TSP ID could also be used as described in clause 6.2.2.6 of TS 23.503 [45].

Further description on User Plane management for 5G VN groups is available in clause 5.8.2.13.

When N6-based traffic forwarding is expected, after creation of a 5G VN group the AF can influence the traffic routing for all the members of the 5G VN group, by providing information identifying the traffic, DNAI(s) suitable for selection and an optional indication of traffic correlation together with a 5G VN External Group ID identifying the 5G VN group in an AF request sent to the PCF, as described in clause 5.6.7. If the optional indication of traffic correlation is provided, it means the PDU sessions of the 5G VN group member UEs should be correlated by a common DNAI in the user plane for the traffic. The PCF transforms the AF request into policies that apply to PDU Sessions of the 5G VN group and sends the policies to the SMF. According to the policies, the SMF (re)selects DNAI(s) for the PDU Sessions and configures their UP paths to route the traffic to the selected DNAI(s). If the policies include the traffic correlation indication, the SMF (re)selects a common DNAI for the PDU Sessions so that the traffic of the 5G VN group is routed to the common DNAI.

NOTE 4: When receiving a new PDU session establishment request for a 5G VN group, to avoid unnecessary N19 tunnels between UPFs, SMF can check previously selected UPFs for the same 5G VN group and decide whether a previously selected UPF could serve the requested PDU session.

NOTE 5: N19 tunnel(s) can be established between a new UPF and other UPF(s) that belongs to a 5G VN group when the new UPF is selected for the 5G VN group during PDU session establishment. The N19 tunnel(s) to a UPF can be released during or after PDU session release when there is no more PDU sessions for a 5G VN group in that UPF. Establishment or release of the N19 tunnels at the UPF is performed within a group-level N4 Session.