Section: 5.8.2.5.3 Support of Ethernet PDU Session type
Content: When configuring an UPF acting as PSA for an Ethernet PDU Session Type, the SMF may instruct the UPF to route the traffic based on detected MAC addresses as follows. - The UPF learns the MAC address(es) connected via N6 based on the source MAC addresses of the DL traffic received on a N6 Network Instance. - The UPF learns the MAC address(es) of UE(s) and devices connected behind, if any, based on the source MAC address contained within the UL traffic received on a PDU Session (N3/N9 interface). - The UPF forwards DL unicast traffic (with a known destination address) on a PDU Session determined based on the source MAC address(es) used by the UE for the UL traffic. - The UPF forwards UL unicast traffic (with a known destination address) on a port (PDU Session or N6 interface) determined based on the source MAC address(es) learned beforehand. - In the case of multicast and broadcast traffic (if the destination MAC address is a broadcast or multicast address): - for DL traffic received by UPF on a N6 Network Instance the UPF should forward the traffic to every DL PDU Session (corresponding to any N4 Session) associated with this Network Instance - for uplink traffic received by UPF over a PDU session on a N3/N9 interface, the UPF should forward the traffic to the N6 interface and downlink to every PDU session (except toward the one of the incoming traffic) associated with the same N6 Network Instance - for uplink and downlink unicast traffic received by UPF, if the destination MAC has not been learnt, the UPF should forward the traffic to every PDU session associated with the same N6 Network Instance and towards the N6 interface. In any case the traffic is not replicated on the PDU Session or the N6 interface of the incoming traffic. NOTE 1: The UPF can consider a PDU Session or a N6 interface to be active or inactive in order to avoid forwarding loops. User data traffic is not sent on inactive PDU sessions or inactive N6 interface. This release of the specification does not further specify how the UPF determines whether a PDU Session or N6 interface is considered active or inactive. NOTE 2: This release of the specification supports only a single N6 interface in a UPF associated with the N6 Network Instance. - if the traffic is received with a VLAN ID, the above criteria apply only towards the N6 interface or PDU session matching the same VLAN ID, unless the UPF is instructed to remove the VLAN ID in the incoming traffic. NOTE 3: This release of the specification supports Independent VLAN Learning (IVL) and does not support Shared VLAN Learning (SVL), as described in IEEE Std 802.1Q [98]. - if the destination MAC address of traffic refers to the same N6 interface or PDU session on which the traffic has been received, the frame shall be dropped. In order to handle scenarios where a device behind a UE is moved from a source UE to a target UE, a MAC address is considered as no longer associated with a UPF interface (source UE's PDU session) when the MAC address has not been detected as Source MAC address in UL traffic for a pre-defined period of time or the MAC address has been detected under a different interface (target UE's PDU Session or N6). NOTE 4: The UPF/NW-TT may also be provided with static filtering entries as described in clause 5.28.3. How the UPF uses the static filtering entry to achieve forwarding of Ethernet frames to one or more egress ports is up to UPF implementation. The externally observable behaviour of 5GS Bridge needs to comply with IEEE Std 802.1Q [98]. For ARP/IPv6 Neighbour Solicitation traffic, a SMF's request to respond to ARP/IPv6 Neighbour Solicitation based on local cache information or to redirect such traffic from the UPF to the SMF overrules the traffic forwarding rules described above. NOTE 5: Local policies in UPF associated with the Network Instance can prevent local traffic switching in the UPF between PDU Sessions either for unicast traffic only or for any traffic. In the case where UPF policies prevent local traffic switching for any traffic (thus for broadcast/multicast traffic) some mechanism such as responding to ARP/ND based on local cache information or local multicast group handling is needed to ensure that upper layer protocol can run on the Ethernet PDU sessions. The SMF may ask to get notified with the source MAC addresses used by the UE, e.g. if the PCF has subscribed to UE MAC address change notifications, as described in TS 23.503[ Policy and charging control framework for the 5G System (5GS); Stage 2 ]  [45]. In order to request the UPF to act as defined above, the SMF may, for each PDU Session corresponding to a Network Instance, set an Ethernet PDU Session Information in a DL PDR that identifies all (DL) Ethernet packets matching the PDU session. Alternatively, for unicast traffic the SMF may provide UPF with dedicated forwarding rules related with MAC addresses notified by the UPF.