A UE can register and establish a PDU Session, with packets forwarded correctly, while the SMF receives no expected usage updates. Check the Usage Reporting Rule (URR): the SMF provisions it over N4 using PFCP, and the UPF measures traffic and reports under the configured conditions. Usage reports support charging, monitoring and policy decisions; complete charging requires additional functions and procedures.
Where URR fits among PFCP rules
A Packet Detection Rule (PDR) identifies traffic and references applicable rules. A Forwarding Action Rule (FAR) specifies forwarding, dropping or buffering; a QoS Enforcement Rule (QER) controls QoS and gating; a Buffering Action Rule (BAR) supplies associated buffering instructions. URR defines usage measurement and reporting, with quota-related behavior where configured.
One PDR can reference multiple URRs, and several PDRs can share a URR. Confirm the matching PDR, its URR ID references and the intended aggregation scope. A URR may exist without a PDR association, but its presence alone does not demonstrate that the test traffic is being measured.
Measurement Method and accounting scope
Measurement Method selects volume, duration, events or supported combinations. Volume Measurement reports total, uplink and downlink octets; an octet is a byte. MNOP in Measurement Information additionally requests packet counts when the UPF supports that feature. Do not confuse byte counters, packet counters and application payload sizes.
Duration measurement depends on the time-metering configuration. Immediate Start Time Metering can start measurement when instructed; otherwise it starts with the first packet. A nonzero Inactivity Detection Time suspends time measurement after the configured inactivity interval and resumes it when traffic returns. Event measurement requires the corresponding event-detection configuration.
For volume measurement, reporting normally covers usage after QoS enforcement. If measurement before QoS enforcement is also requested, separate Usage Reports distinguish the two scopes through Usage Information. Thresholds apply after QoS enforcement. Compare the same direction, accounting window and processing scope before declaring a counter mismatch.
Reporting triggers, thresholds and quotas
Reporting Triggers must be read with their parameters: PERIO uses Measurement Period; VOLTH, TIMTH and EVETH concern volume, time and event thresholds; VOLQU, TIMQU and EVEQU concern quotas. START and STOPT report traffic start and stop under the applicable detection conditions. Quota Holding Time concerns inactivity after a grant; it is not the periodic reporting timer.
| Parameter | Meaning and boundary |
|---|---|
| Volume Threshold | A reporting boundary, not a traffic allowance or an automatic packet cutoff. |
| Volume Quota | An allocated usage allowance. Exhaustion can require stopping or limiting forwarding under the specified quota behavior. |
| Measurement Period | The interval used for requested periodic usage reports. |
| Monitoring Time | A boundary separating usage before and after a specified time, with applicable subsequent thresholds or quotas. |
Quota behavior is more than a notification. Under TS 29.244, exhausting a provisioned quota can stop forwarding or allow only limited traffic according to operator policy. When supported and provisioned, FAR ID for Quota Action selects a substitute FAR for dropping, buffering or redirecting traffic. QER and FAR/BAR responsibilities still remain distinct; a threshold-only URR is not a bandwidth limiter.
When both threshold and quota are provisioned, enabling only the threshold trigger does not imply a second report at quota exhaustion. With both triggers enabled, the reviewed Release 18 specification provides reporting at both boundaries; older release behavior can differ. Inspect the implemented release, capabilities, exemptions and complete rule set.
How a Usage Report reaches the SMF
The UPF can send a PFCP Session Report Request with Report Type indicating a Usage Report. Inspect URR ID, UR-SEQN and Usage Report Trigger, then Volume Measurement or Duration Measurement as applicable. Start Time, End Time and packet timestamps help delimit the interval. A START-only report need not contain a nonzero usage measurement.
The SMF returns a PFCP Session Report Response; inspect its Cause. Successful delivery does not prove successful charging or a quota renewal. The SMF can separately send a PFCP Session Modification Request to update rules. Usage Reports can also appear in PFCP Session Modification Response and PFCP Session Deletion Response under their applicable procedures, so searching only unsolicited requests can miss accounting records.
Monitoring Time can produce separate reports for usage before and after the boundary with the same URR ID. Retain Usage Information and sequence information, distinguish retransmissions from new reports, and reconcile the reported intervals rather than treating every value as a lifetime counter.
Example: a 10240-byte volume threshold
Assume volume measurement, VOLTH and a total Volume Threshold of 10240 bytes with TOVOL set. The UPF reports when the measured total reaches that boundary; the value is not a 10240-byte allowance. Packet granularity can produce a report above the threshold. The configured quota, if any, must be analyzed separately.
A trace checklist for missing or unexpected usage
Identify the PFCP session and actual matching PDR; check URR references and aggregation across uplink and downlink PDRs.
Check Measurement Method, measurement activation, MNOP support, time-metering settings and before/after-QoS scope.
Pair each requested trigger with its threshold, quota or timer; check Monitoring Time and subsequent values.
Trace requests and responses, Cause, URR ID, UR-SEQN, reported intervals and retransmissions; include modification and deletion responses.
If reporting succeeds, inspect SMF processing, charging integration, renewed quota and any applicable QER/FAR changes. Verify actual forwarding behavior separately.
FAQs
Can one URR measure both traffic directions?
Yes. Relevant uplink and downlink PDRs can reference the same URR. Check the intended aggregation rather than assuming that one URR always represents one direction or one service.
Does a Usage Report confirm that a customer was billed?
No. It confirms a UPF reporting event. Charging correlation, rating and billing outcomes require evidence from the corresponding control-plane and charging systems.
Should all URR reports be added together?
Not blindly. Reports can describe different intervals, monitoring boundaries or before/after-QoS scopes, and retransmissions can repeat a report. Correlate identifiers and measurement context before aggregation.
