5.29.3 PDU Session management

Session management as defined for 5GS in clause 5.6 is applicable to 5G-VN-type services with the following clarification and enhancement:

• A UE gets access to 5G LAN-type services via a PDU Session of IP PDU Session type or Ethernet PDU Session type.
• A PDU Session provides access to one and only one 5G VN group. The PDU Sessions accessing to a certain 5G VN group should all anchor at the same network, i.e. the common home network of 5G VN group members.
• A DNN and S-NSSAI is associated with a 5G VN group.
• A dedicated SMF, a dedicated SMF Set or multiple SMF (Sets) can be responsible for all the PDU Sessions for communication of a certain 5G VN group. Multiple SMF (Sets) may apply for a 5G VN group extended over a large area, bigger than the service area of any SMF Set serving the DNN/S-NSSAI of the 5G VN group. SMF selection is described in clause 6.3.2.

NOTE 1: If a dedicated SMF (Set) is used to serve a 5G VN, the network is configured so that the same SMF (Set) is always selected for a certain 5G VN group, e.g. only one SMF, or SMFs in one SMF Set, registers on the NRF with the DNN/S-NSSAI used for a given 5G VN group.

NOTE 2: Having a dedicated SMF serving a 5G VN does not contradict that redundancy solutions can be used to achieve high availability. If SMF Set(s) serve the 5G VN group, high availability is achieved by the set functionality.

• In the case that more than one SMF sets or SMF instances in a SMF Set are responsible for all the PDU Sessions for communication of a certain 5G VN group to enable SMF redundancy for reliability of the 5G VN group communication:
• The associations between one or more SMF Sets and the DNN, S-NSSAI of the associated 5G VN group is registered and discovered in NRF.
• The SMFs that registered to associate with the DNN, S-NSSAI of the 5G VN group should be available in the LADN service area of the 5G VN group.
• The UE provides the DNN and S-NSSAI associated with the 5G VN group to access the 5G LAN-type services for that 5G VN, using the PDU Session Establishment procedure described in clause 4.3.2 of TS 23.502 [3].
• During establishment of the PDU Session, secondary authentication as described in clause 5.6.6 and in clause 4.3.2.3 of TS 23.502 [3], may be performed in order to authenticate and authorize the UE for accessing the DNN and S-NSSAI associated with the 5G VN group. Authentication and authorization for a DNN and S-NSSAI using secondary authentication implies authentication and authorization for the associated 5G VN group. There is no 5G VN group specific authentication or authorization defined.
• The SM level subscription data for a DNN and S-NSSAI available in UDM, as described in clause 5.6.1, applies to the DNN and S-NSSAI associated to a 5G VN group.
• Session management related policy control for a DNN and S-NSSAI as described in TS 23.502 [3], is applicable to the DNN and S-NSSAI associated to a 5G VN group. This includes also usage of URSP, for the UE to determine how to route outgoing traffic to a PDU Session for the DNN and S-NSSAI associated to a 5G VN group.
• Session and service continuity SSC mode 1, SSC mode 2 and SSC mode 3 as described in clause 5.6.9 are applicable to N6-based traffic forwarding of 5G VN communication within the associated 5G VN group.
• A PDU Session provides unicast, broadcast and multicast communication for the DNN and S-NSSAI associated to a 5G VN group. The PSA UPF determines whether the communication is for unicast, broadcast or multicast based on the destination address of the received data and performs unicast, broadcast or multicast communication handling.
• During the PDU Session Establishment procedure, the SMF retrieves SM subscription data related to 5G-VN type service from the UDM as part of the UE subscription data for the DNN and S-NSSAI.
• In order to realize N19 traffic routing in the case that a single SMF (or single SMF Set) is serving the 5G VN, the SMF (or SMF Set) correlates PDU sessions established to the same 5G VN group and uses this to configure the UPF with the group level N4-session including packet detection and forwarding rules for N19 tunnelling forwarding.

NOTE 3: In the case of a SMF Set serving a 5G VN, implementation dependent mechanism can be used between SMF(s) that are part of a SMF Set to control the N19 configuration.

• In order to realize N6/N19 traffic routing between PSA UPFs in case multiple SMF Sets are serving the 5G VN, traffic forwarding between UPFs belonging to different SMF (Set)s can be realized via User Plane tunnels that are configured using OAM between UPFs served by different SMF (Set)s. How to implement the user plane tunnels and traffic forwarding configured between these UPFs is up to network implementation and deployment and is out of scope of this specification.