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The UPF (User Plane Function) manages the routing of user traffic and implements traffic filtering functions.

The PSA UPF is the traffic gateway connecting the 5GC network to the DN (Data Network). The PSA constitutes the anchor point for inter-UPF mobility.

The UPF is the anchor point for traffic when the mobile is moving from one NG-RAN node to another.

The UPF measures the quantity of data consumed for each UE.

The UPF can also implement traffic optimization functions and NAT (Network Address Translation), either from a private IPv4 address to a public IPv4 address, or from an IPv4 address to an IPv6 address and vice versa.

When the UPF receives data from the DN:

1 – in the absence of a routing context concerning the incoming flow, the UPF informs the SMF. The UPF either stores the data or transmits it to the SMF;

2 – in the presence of a routing context stored at the UPF level concerning the incoming flow, the flow is either transmitted to an NG-RAN node or to another UPF.

The UPF implements traffic routing rules by configuring the DSCP field of the IP based on the QFI. The QFI is defined by QoS rules which are injected by the SMF to the UPF when establishment of a session is requested. For each incoming piece of data, the UPF performs a traffic inspection (DPI (Deep Packet Inspection)) and classifies the packets into IP flow groups according to the SDF (Service Data Flow) service templates.

The UPF is a branch point supporting the multi-homing function.

The UPF performs replications of the mobile traffic data within the framework of lawful interception.