Content for  TS 23.501  Word version:  19.1.0

The service requirements for 5G LAN-type service are specified in TS 22.261. A 5G Virtual Network (VN) group consists of a set of UEs using private communication for 5G LAN-type services.

5G System supports management of 5G VN Group identification and membership (i.e. definition of 5G VN group identifiers and membership) and 5G VN Group data (i.e. definition of 5G VN group data). The 5G VN Group management can be configured by a network administrator or can be managed dynamically by AF. A 5G VN group is characterized by the following:

• 5G VN group identities: External Group ID and Internal Group ID are used to identify the 5G VN group.
• 5G VN group membership: The 5G VN group members are uniquely identified by GPSI. The group as described in clause 5.2.3.3.1 of TS 23.502 is applicable to 5G LAN-type services.
• 5G VN group data. The 5G VN group data may include the following parameters: PDU session type, DNN, S-NSSAI and Application descriptor, the indication that the 5G VN group is associated with 5G VN group communication, Information related with secondary authentication / authorization (e.g. to enable IP address assignment by the DN-AAA), Maximum Group Data Rate, User Plane Security Policy.
  The Information related with secondary authentication / authorization corresponds to the procedures described in clause 5.6.6; it allows e.g. the AF to provide DN-AAA server addressing information and possibly to request the SMF to get the UE IP address from the DN-AAA server.

In order to support dynamic management of 5G VN Group identification and membership, the NEF exposes a set of services to manage (e.g. add/delete/modify) 5G VN groups and 5G VN members. The NEF also exposes services to dynamically manage 5G VN group data. An AF can request provisioning of traffic characteristics, QoS parameters and monitoring of QoS parameters for a 5G VN group as described in clause 6.1.3.28 of TS 23.503. A 5G VN group is identified by the AF using External Group ID. The NEF provides the External Group ID to UDM. The UDM maps the External Group ID to Internal Group ID. For a newly created 5G VN Group, an Internal Group ID is determined by the UDM based on implementation specific means. The NEF can retrieve the Internal Group ID from UDM via Nudm_SDM_Get service operation (External Group ID, Group Identifier translation). An External Group ID for a 5G VN group corresponds to a unique set of 5G VN group data parameters. The 5G VN group configuration is either provided by OA&M or provided by an AF to the NEF. When configuration is provided by an AF, the procedures described in clause 4.15.6.2 of TS 23.502 apply for storing the 5G VN group identifiers, group membership information and group data in the UDR, as follows:

• The NEF provides the External Group ID, 5G VN group membership information and 5G VN group data to the UDM.
• The UDM updates the Internal Group ID-list of the corresponding UE's subscription data in UDR, if needed.
• The UDM updates the Group Identifier translation in the Group Subscription data with the Internal Group ID, External Group ID and list of group members, if needed.
• The UDM stores/updates the 5G VN group data (PDU session type, DNN and S-NSSAI, Application descriptor, the indication that the 5G VN group is associated with 5G VN group communication, Information related with secondary authentication / authorization, Maximum Group Data Rate, User Plane Security Policy) in UDR.

An AF may also configure and update the service area, QoS for the 5G VN group as described in clause 5.20b as well as other parameters (e.g. Expected UE Behaviour parameters, Network Configuration parameters, ECS Address Configuration Information, etc.) for a 5G VN group as described in clause 4.15.6 of TS 23.502. If a UE is member of a 5G VN Group, UDM retrieves UE subscription data and corresponding 5G VN group data from UDR, and provides the AMF and SMF with UE subscription data with 5G VN group data included. If the 5G VN group data contains the indication that the 5G VN group is associated with 5G VN group communication, the SMF may apply the 5G VN group communication as defined in clauses 5.29.3 and 5.29.4 for the PDU Sessions accessing to the 5G VN group. The PCF generates URSP rules based on 5G VN group data. The PCF retrieves 5G VN group data from UDR. The PCF(s) that have subscribed to modifications of 5G VN group data receive(s) a Nudr_DM_Notify notification of 5G VN group data change from the UDR as defined in TS 29.505. The PCF receives from the AMF at the UE Policy association establishment the Internal Group ID(s) corresponding to a UE, so that PCF identifies the 5G VN group data that needs to be used to generate URSP rules to the UE. If the PCF is made aware of a change of UE Internal Group Identifier(s) as defined in TS 29.525 or change of 5G VN group membership as defined in TS 29.505, or both, the PCF then may update the URSP rules for the impacted 5G VN group members. If the PCF receives the Maximum Group Data Rate as part of the 5G VN group data, it performs the group related policy control as described in clauses 6.1.5 and 6.2.1.11 of TS 23.503. An AF may update the UE Identities of the 5G VN group at any time after the initial provisioning. An AF may subscribe to notification of the group status changes for the 5G VN group as described in clause 5.20. The DNN, S-NSSAI, User Plane Security Policy provided within 5G VN group data cannot be modified after the initial provisioning. In this Release of the specification, the home network of the 5G VN group members is same. In this Release of the specification, only a 1:1 mapping between (DNN, S-NSSAI) combination and 5G VN group is supported. The PCF delivers 5G VN group configuration information (DNN, S-NSSAI, PDU session type) to the UE for each GPSI that belongs to a 5G VN group. The 5G VN group configuration information is delivered in the URSP from the PCF to the UE using the UE Configuration Update procedure for transparent UE Policy delivery as described in clause 4.2.4.3 of TS 23.502 and clause 6.1.2.2 of TS 23.503.

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.
• 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.
• 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, 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, 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.
• 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.

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;
  • 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.
• 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.

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.