Statistics reporting uses the PFCP Usage Reporting Rule (URR) mechanism. The BNG UPF supports a single URR to count all statistics that are related to a session. The BNG UPF supports sending the following statistics for the URR:
Aggregate octet counters are always signaled.
Aggregate packet counters are signaled, if enabled by the CPF.
All counters, including aggregates, are based on QoS counters and are therefore affected by QoS modifiers, such as the packet-byte-offset command.
The BNG UPF sends reports for a URR in the following cases:
the BNG CPF explicitly queries the UPF via a PFCP Session Modification Request
the periodic URR reporting is enabled and the BNG UPF sends unsolicited PFCP Session Report Request messages
PFCP statistics are reported in an incremental manner. This means that only new statistics after the last report are signaled. To achieve this, the BNG UPF baselines the counters on every report. Consequently, it is not possible to manually clear statistics on the BNG UPF using the clear service statistics subscriber command. Other operational commands (for example, show service active-subscribers detail) only show the accumulated statistics on the BNG UPF.
Because statistics are based on QoS counters, sessions sharing the same SLA Profile Instance (SPI) also share statistics, and a report for one session baselines the counters for the entire SPI. As a result, per-session statistics on the BNG CPF are not correct when sharing an SPI; however, their aggregate counts are correct. The BNG CPF must provide the appropriate aggregate level (for example, subscriber-level accounting). When an SPI changes, the BNG UPF reports the final SPI statistics in PFCP if instructed to do so by the BNG CPF.
Hardware failures are automatically taken into account for statistics reporting. Statistics generated after the last report are irretrievably lost. However, as a result of the incremental reporting, the BNG CPF does not lose any older counters and does not see a sudden reset. That is, aggregate counters on the BNG CPF never decrease as a result of a hardware failure. However, the BNG UPF local statistics as seen in show commands reset upon a hardware failure, and therefore a mismatch of BNG CPF counters may result.