Section: 6.2.3 UPF
Content: The User plane function (UPF) includes the following functionality. Some or all of the UPF functionalities may be supported in a single instance of a UPF: - Anchor point for Intra-/Inter-RAT mobility (when applicable). - Allocation of UE IP address/prefix (if supported) in response to SMF request. - External PDU Session point of interconnect to Data Network. - Packet routing & forwarding (e.g. support of Uplink classifier to route traffic flows to an instance of a data network, support of Branching point to support multi-homed PDU Session, support of traffic forwarding within a 5G VN group (UPF local switching, via N6, via N19)). - Packet inspection (e.g. Application detection based on service data flow template and the optional PFDs received from the SMF in addition). - User Plane part of policy rule enforcement, e.g. Gating, Redirection, Traffic steering). - Lawful intercept (UP collection). - Traffic usage reporting. - QoS handling for user plane, e.g. UL/DL rate enforcement, Reflective QoS marking in DL. - Uplink Traffic verification (SDF to QoS Flow mapping). - Transport level packet marking in the uplink and downlink. - Downlink packet buffering and downlink data notification triggering. - Sending and forwarding of one or more "end marker" to the source NG-RAN node. - Functionality to respond to Address Resolution Protocol (ARP) requests and / or IPv6 Neighbour Solicitation requests based on local cache information for the Ethernet PDUs. The UPF responds to the ARP and / or the IPv6 Neighbour Solicitation Request by providing the MAC address corresponding to the IP address sent in the request. - Packet duplication in downlink direction and elimination in uplink direction in GTP-U layer. - NW-TT functionality. - High latency communication, see clause 5.31.8. - ATSSS Steering functionality to steer the MA PDU Session traffic, refer to clause 5.32.6. NOTE: Not all of the UPF functionalities are required to be supported in an instance of user plane function of a Network Slice. - Inter PLMN UP Security (IPUPS) functionality, specified in clause 5.8.2.14. - Event exposure, including exposure of network information, i.e. the QoS monitoring information, as specified in clause 5.8.2.18, events as specified in clause 5.2.26.2 of TS 23.502[ Procedures for the 5G System (5GS) ]  [3], exposure of data collected for analytics, as specified in clause 5.2.26.2 of TS 23.502[ Procedures for the 5G System (5GS) ]  [3] and exposure of the TSC management information as specified in clause 5.8.5.14. - Exposure of the UE information, e.g. UE IP address translation information as specified in clause 5.2.26.3 of TS 23.502[ Procedures for the 5G System (5GS) ]  [3] and clause 4.15.10 of TS 23.502[ Procedures for the 5G System (5GS) ]  [3] if Network address translation (i.e. NAT) functionality of the UE IP address is deployed within UPF. - Support PDU Set Handling as defined in clause 5.37.5.