5G (NR) Terminal Supported PDU Sessions (Continuation 1)

In 5G, a PDU Session is a logical connection between the UE and the DN (Internet or enterprise network), specifically for data (traffic) transmission and supporting services such as browsing or voice (VoNR).

I. Ethernet Preamble and Frame Start Delimiter will not be sent through the 5GS, where:

• For uplink traffic, the UE will strip the preamble and Frame Check Sequence (FCS) from the Ethernet frame.
• For downlink traffic, the PDU session anchor will strip the preamble and Frame Check Sequence (FCS) from the Ethernet frame.

II. MAC and IP Addresses: The 5GC will not assign MAC or IP addresses to the UE in the PDU session. The PSA should store the MAC address received from the UE and associate it with the corresponding PDU session.

III. SMF and VLAN: The SMF in the 5GC can receive a list of allowed VLAN tags (up to 16 VLAN tags) from the DN-AAA, or it can configure the allowed VLAN tag values ​​locally. The SMF can also configure VLAN processing instructions (e.g., LAN tags to be inserted or deleted, S-TAGs to be inserted or deleted). Considering this, the SMF determines the VLAN processing method for the PDU session and instructs the UPF to accept or discard UE traffic based on the allowed VLAN tags, and process VLAN tags through PDR (outer header removal) and FAR (outer header creation for UPF application forwarding policy), for example:

• The UPF can insert (for uplink traffic) and remove (for downlink traffic) S-TAGs on the N6 or N19 or internal interface "5G VN Internal" for processing traffic to and from the UE.
• When there is no VLAN in the traffic to the UE, the UPF can insert (for uplink traffic) and remove (for downlink traffic) VLAN tags on the N6 interface.
• When the UPF processes uplink or downlink traffic from the UE, the UPF can discard any UE traffic that does not contain any allowed VLAN tags.

IV. Traffic Steering (Forwarding): In 5G, this can be used to steer traffic to N6-LAN, and also for N6-based traffic forwarding related to 5GVN services as described in Section 5.29.4. Except for specific conditions related to PDU session support over W-5GAN as defined in TS 23.316 [84], the UPF shall not remove VLAN tags sent by the UE, nor shall it insert VLAN tags for traffic sent to the UE; where:

• PDU containing VLAN tags can only be exchanged within the same VLAN through the PDU session anchor.
• The UE can obtain the MTU of the Ethernet frame payload it should consider from the SMF during PDU session establishment (see Section 5.6.10.4).

V. Connection Mode: The UE can connect to its connected LAN in bridge mode; therefore, the uplink (UL) source and destination MAC addresses of different frames may be different within the same PDU session. The downlink (DL) destination MAC addresses of different frames may also be different within the same PDU session.

VI. IP Allocation and MAC Addresses: Entities on the LAN connected to the 5GS may have IP addresses allocated by the DN, but the IP layer is considered an application layer and is not part of the Ethernet PDU session. The 5GS does not support the use of MAC addresses or (if VLANs are applied) combinations thereof across multiple PDU sessions for the same DNN S-NSSAI.

VII. UE Authentication: In the R18 specification version, only the UE connected to the 5GS is authenticated, not the devices behind it; furthermore:

• The R18 specification version does not guarantee a loop-free Ethernet network. Deployment scenarios need to be verified individually to ensure that Ethernet loops are avoided.
• The R18 specification version does not guarantee that Ethernet will respond correctly and quickly to topology changes. Deployment scenarios need to be verified individually to understand how they respond to topology changes.