How it Works
This section describes how UPF supports offline charging of usage data.
To implement offline charging, the charging information is sent to the SMF only during PFCP session deletion.
Time and volume-based reporting is supported in the offline charging implementation. The following call flow illustrates offline charging in UPF.

During the PFCP session deletion, UPF transfers the following charging information to the SMF:
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Timestamp of the first and last data packet
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Duration measurement – This IE specifies the time difference between URR creation and usage-reporting
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Volume measurement – This IE specifies the uplink data, downlink data and the total bytes transferred from the UPF to gNodeB.