5.8.2.13.3 Support for user plane traffic replication in a 5G VN

5.8.2.13.3.1 User plane traffic replication based on UPF internal functionality

For Ethernet PDU Sessions, the SMF may instruct the UPF to route traffic to be replicated as described in clause 5.8.2.5.

For IP PDU Session types, the SMF may instruct the UPF to manage IP multicast traffic as described in clauses 4.6.6 and 7.7.1 of TS 23.316 [84]. The UPF replicates the IP multicast traffic received from PDU Sessions or N6 interface and sends the packets over other PDU Sessions and other N6 interface subscribed to the IP Multicast groups.

Mechanisms described in clauses 4.6.6 and 7.7.1 of TS 23.316 [84] apply to support 5G VN group communication with following clarifications:

• These mechanisms are not limited to Wireline access and can apply on any access,
• IP Multicast traffic allowed for a PDU Session is not meant for IPTV services reachable over N6,
• IGMP /MLD signalling does not relate with STB or 5G-RG: Clauses 4.6.6 and 7.7.1 of TS 23.316 [84], apply to UE members of a 5G VN group instead of 5G-RG and
• Clauses 7.7.1.1.2 and 7.7.1.1.4 of TS 23.316 [84] are not applicable to 5G VN groups: members of the 5G VN groups may receive any multicast traffic associated with the (DNN, S-NSSAI) of the 5G VN group.
• UPF exchange of signalling such as PIM (Protocol-Independent Multicast) may apply as defined in TS 23.316, with following clarification:
• PIM signalling is generally exchanged over N6 but may be sent towards the PDU Session supporting the source address of multicast traffic identified by IGMP / MLD signalling for Source Specific Multicast. In the case of IGMP / MLD signalling not related with Source Specific Multicast no PIM signalling is sent towards any PDU Session

5.8.2.13.3.2 User plane traffic replication based on PDRs with replication instructions

Alternatively, for IP or Ethernet type data communication, the SMF instructs the UPF via PDRs and FARs how to replicate user plane traffic.

The mechanism is supported in the following conditions:

• When N19 is used, there is a full mesh of N19 tunnels between UPFs controlled by each SMF Set serving the 5G VN group;
• There is no support for forwarding a broadcast/multicast packet with source address not known to SMF/UPF.
• Each UPF supports one N6 interface instance towards the data network, or only supports N19-based forwarding without N6;
• Multicast group formation of selected members of a 5G VN for Ethernet type data communication is not described in this release of the specification.

In this case, when the UPF receives a broadcast packet of a 5G VN group from N19 or N6, it shall distribute it to all 5G VN group members connected to this UPF. When the UPF receives a broadcast packet from a UE (source UE) via PDU Session associated with a 5G VN group, it shall distribute it to:

• All 5G VN group members (except the source UE) connected to this UPF via local switch; and
• All 5G VN group members connected to other UPFs via N19-based forwarding or N6-based forwarding; and
• The devices on the DN via N6-based forwarding.

To enable broadcast traffic forwarding of a 5G VN group in a UPF, the following applies:

• The SMF provides group-level N4 Session and each 5G VN group member' N4 Session with the PDR that detect the broadcast packet sent via "internal interface". When UPF receives the broadcast packets sent via "internal interface", it matches the broadcast packet against all PDRs installed at the "internal interface". A successful matching with a PDR that detect the broadcast packet instructs the UPF to continue the lookup of the other PDRs. A matching PDR that detects the broadcast packet shall instruct the UPF to duplicate the broadcast packet and perform processing (using associated FAR, URR, QER) on the copy instead of the original packet if the broadcast packet does not satisfy the packet replication skip information, otherwise the PDR instructs the UPF to skip the processing of the broadcast packet.
• The broadcast packets received from N19 or N6 are forwarded to the UPF internal interface together with a N19 or N6 indication.
• The SMF provides for each 5G VN group member' N4 Session (i.e. N4 session corresponding to PDU Session) the following N4 rules that enable the processing of broadcast packets towards this UE.
• in order to detect the traffic, a PDR containing Source Interface set to "5G VN internal", Destination Address set to the broadcast address, the Packet replication skip information set to the IP/MAC address (es) of this 5G VN group member and the indication to carry on matching; and
• in order to forward the traffic, a FAR containing Outer Header Creation indicating the PDU Session tunnel information and Destination Interface set "access side".
• The SMF configures the group-level N4 Session for processing packets received from a N19 tunnel with the following N4 rules for each N19 tunnel.
• in order to detect the traffic, a PDR containing Source Interface set to "core side", Destination Address set to the broadcast address and CN Tunnel Information set to N19 tunnel header (i.e. N19 GTP-U TEID); and
• in order to forward the traffic, a FAR containing Destination Interface set to "5G VN internal", Outer Header Creation with the N19 indication.
• The SMF provides for the group-level N4 Session the following N4 rules that enable the processing of broadcast packets towards the other UPFs.
• in order to detect the traffic, a PDR containing Source Interface set to "5G VN internal", Destination Address set to the broadcast address, the Packet replication skip information set to the N19 indication and the indication to carry on matching; and
• in order to forward the traffic to each involved UPF via the corresponding N19 tunnel, a FAR containing "Duplication" instruction, Outer Header Creation indicating the N19 tunnel information, Destination Interface set to "core side".
• The SMF configures the group-level N4 Session for processing packets received from N6 with the following N4 rules.
• in order to detect the traffic, a PDR containing Source Interface set to "core side" and Destination Address set to the broadcast address; and
• in order to forward the traffic, a FAR containing Destination Interface set to "5G VN internal", Outer Header Creation with the N6 indication.
• The SMF provides for the group-level N4 Session the following N4 rules that enable the processing of broadcast packets towards N6.
• in order to detect the traffic, a PDR containing Source Interface set to "5G VN internal" and Destination Address set to the broadcast address and the Packet replication skip information set to the N6 indication; and
• in order to forward the traffic to N6, a FAR containing Destination Interface set to "core side".

In this case, to enable multicast traffic forwarding of a 5G VN group in a UPF, broadcast traffic forwarding of a 5G VN applies to multicast traffic forwarding of a 5G VN with the following modifications:

• The SMF installs PDRs for the multicast address instead of the broadcast address.
• The PDRs and FARs are installed for PDU Sessions corresponding to the members of the multicast group.
• In addition, the SMF installs the PDR identifying IGMP/MLD signalling for each 5G VN group member' N4 Session and a URR with a Reporting Trigger set to "IGMP reporting" for IGMP or set to "MLD reporting" for MLD. Based on the IP Multicast address in "IP multicast join" or "IP multicast leave" reports received from UPF, the SMF manipulates (delete or add) the PDR identifying the multicast traffic for the reported IP Multicast address at the corresponding 5G VN group member' N4 Session and if required at the group-level N4 Session at the UPF(s) of the 5G VN group.