Supported E2 Metrics

What is E2SM-KPM?

E2SM-KPM (E2 Service Model, Key Performance Measurements) is an O-RAN Alliance service model that lets a near-RT RIC subscribe to performance measurements from an E2 node. It is carried over the E2 interface using E2AP and is defined in O-RAN.WG3.E2SM-KPM-R003-v03.00.

The RIC sends a subscription request specifying which metrics to collect, at what reporting interval, and using which report style. The gNB's E2 agent collects those measurements internally and sends periodic RIC Indication messages back to the RIC with the results.

The three main concepts in an E2SM-KPM subscription are:

• Report Style: determines how measurements are aggregated (node-level, per-UE, or conditional).
• Metric name: identifies the specific measurement, using names from the 3GPP TS 28.552 or O-RAN specifications.
• Labels: optional dimensions attached to a measurement (per-PLMN, per-5QI, per-slice). If no label is requested, the aggregate value is returned.

To enable E2SM-KPM, configure the gNB as described in the Near-RT RIC tutorial.

Metric Coverage

OCUDU implements E2SM-KPM v3.00. The table below shows the current coverage of the full 3GPP and O-RAN metric specifications.

Specification	Defined	Supported
3GPP TS 28.552	278	24
O-RAN WG3	9	3
Total	287	27

The metric set grows with each release as new internal measurements are exposed through the E2 interface.

Report Service Styles

E2SM-KPM defines six report styles that control how measurements are aggregated and delivered. All six are supported.

Style	Name	Description
1	E2 Node Measurement	Node-level aggregate measurements across all UEs
2	E2 Node Measurement for a single UE	Measurements filtered to one specific UE
3	Condition-based, UE-level E2 Node Measurement	UE-level measurements for UEs matching subscribed conditions
4	Common Condition-based, UE-level Measurement	UE-level measurements across multiple metric types with shared conditions
5	E2 Node Measurement for multiple UEs	Measurements for a named set of UEs
255	Multiple report measurements	Multiple simultaneous subscriptions (Integrated level)

Style 255 is functional but has not been tested against available RICs due to limited xApp support for this mode.

For styles 3 and 4, condition checking is not yet implemented; all active UEs are included in reports regardless of the conditions specified in the subscription request.

Supported Metrics

Each metric is produced by one of three E2 agent instances in the gNB. Each must be enabled separately in the gNB configuration:

• DU: the Distributed Unit E2 agent (enable_du_e2: true)
• CU-CP: the CU Control Plane E2 agent (enable_cu_cp_e2: true)
• CU-UP: the CU User Plane E2 agent (enable_cu_up_e2: true)

Most metrics support the NO_LABEL (aggregate) variant only. Where a narrower restriction applies, it is noted in the table.

Throughput and Data Volume

Metric	Source	Unit	Notes
DRB.UEThpDl	DU	kbps	DL per-UE throughput; NO_LABEL only
DRB.UEThpUl	DU	kbps	UL per-UE throughput; NO_LABEL only
DRB.RlcSduTransmittedVolumeDL	DU	kbit	DL RLC transmitted SDU volume (O-RAN); NO_LABEL only
DRB.RlcSduTransmittedVolumeUL	DU	kbit	UL RLC transmitted SDU volume (O-RAN); NO_LABEL only

Latency and Delay

Metric	Source	Unit	Notes
DRB.AirIfDelayUl	DU	ms	UL air interface delay per DRB; NO_LABEL only
DRB.RlcDelayUl	DU	ms	UL RLC delay per DRB; NO_LABEL only
DRB.PdcpReordDelayUl	CU-UP	ms	UL PDCP reordering delay; NO_LABEL only
DRB.RlcSduDelayDl	DU	0.1 ms	DL RLC SDU delay; NO_LABEL only

Physical Resource Block Utilization

Metric	Source	Unit	Notes
RRU.PrbTotDl	DU	%	Total DL PRBs in the scheduling period; NO_LABEL only
RRU.PrbTotUl	DU	%	Total UL PRBs in the scheduling period; NO_LABEL only
RRU.PrbUsedDl	DU	—	DL PRBs occupied; NO_LABEL only
RRU.PrbAvailDl	DU	—	DL PRBs available; NO_LABEL only
RRU.PrbUsedUl	DU	—	UL PRBs occupied; NO_LABEL only
RRU.PrbAvailUl	DU	—	UL PRBs available; NO_LABEL only

Packet Loss and Success Rates

Metric	Source	Unit	Notes
DRB.PacketSuccessRateUlgNBUu	DU	—	UL packet success rate at the Uu interface; NO_LABEL only
DRB.RlcPacketDropRateDl	DU	—	DL RLC packet drop rate; NO_LABEL only
DRB.RlcPacketDropRateDL	DU	—	DL RLC packet drop rate (O-RAN); spec name is DRB.RlcPacketDropRateDLDist — subscribe using DRB.RlcPacketDropRateDL; NO_LABEL only

RRC Connections

These metrics are reported at E2 node level only. UE-level granularity and per-PLMN labels are not supported.

Metric	Source	Unit	Notes
RRC.ConnMean	CU-CP	—	Mean number of RRC-connected UEs
RRC.ConnMax	CU-CP	—	Peak number of RRC-connected UEs
RRC.ConnEstabAtt	CU-CP	—	RRC connection setup attempts
RRC.ConnEstabSucc	CU-CP	—	RRC connection setup successes
RRC.ConnEstabFailCause	CU-CP	—	RRC setup failure cause; only the NetworkReject sub-metric is exposed
RRC.ReEstabAtt	CU-CP	—	RRC re-establishment attempts
RRC.ReEstabSuccWithUeContext	CU-CP	—	RRC re-establishment successes with retained UE context

UE Context

Metric	Source	Unit	Notes
UECNTX.ConnEstabAtt	CU-CP	—	UE context setup attempts; node-level, NO_LABEL only
UECNTX.ConnEstabSucc	CU-CP	—	UE context setup successes; node-level, NO_LABEL only

RACH

Metric	Source	Unit	Notes
RACH.PreambleDedCell	DU	—	Dedicated RACH preambles received at cell level; NO_LABEL only

Extending the Metric Set

Adding support for a new metric involves three steps.

All relevant files are under lib/e2/e2sm/e2sm_kpm/.

Step 1: Confirm the internal measurement exists

Each getter reads from the in-memory data that the provider receives from the gNB stack. Before writing any E2 code, confirm the value you need is already being produced by the relevant subsystem:

Provider	Member variables	Source structs
DU	last_ue_metrics (scheduler per-slot PRB and PRACH data); ue_aggr_rlc_metrics (RLC SDU/PDU byte counts and delays)	scheduler_cell_metrics, rlc_metrics
CU-CP	cu_cp_metrics (RRC connection and UE context counters)	cu_cp_metrics_report
CU-UP	ue_aggr_pdcp_metrics (PDCP reordering and delay); ue_aggr_f1u_metrics (F1-U counters)	pdcp_metrics_container, f1u_metrics_container

If the value is not present in these structs, it must first be added to the relevant gNB subsystem and plumbed into the provider via its report_metrics() entry point.

Step 2: Implement the getter function

Add a getter method to the provider class that corresponds to where the data lives. All getters share the same signature:

bool get_my_metric(
    const asn1::e2sm::label_info_list_l          label_info_list,
    const std::vector<asn1::e2sm::ue_id_c>&      ues,
    const std::optional<asn1::e2sm::cgi_c>       cell_global_id,
    std::vector<asn1::e2sm::meas_record_item_c>& items);

The body follows the same pattern in every getter:

1. If ues is empty, compute one aggregate (node-level) value and push it into items.
2. If ues is non-empty, iterate over them and push one record per UE from the stored per-UE data.
3. Return true if at least one record was added, false if no data was available yet.

Existing getters such as get_prb_avail_dl (DU, node-level) and get_drb_dl_mean_throughput (DU, per-UE) are good templates. Declare the new method in the corresponding header file alongside the existing getter declarations:

Provider class	Header	Implementation
e2sm_kpm_du_meas_provider_impl	e2sm_kpm_du_meas_provider_impl.h	e2sm_kpm_du_meas_provider_impl.cpp
e2sm_kpm_cu_cp_meas_provider_impl	e2sm_kpm_cu_meas_provider_impl.h	e2sm_kpm_cu_meas_provider_impl.cpp
e2sm_kpm_cu_up_meas_provider_impl	e2sm_kpm_cu_meas_provider_impl.h	e2sm_kpm_cu_meas_provider_impl.cpp

Step 3: Register the metric

In the constructor of the provider class, add a call to supported_metrics.emplace():

supported_metrics.emplace(
    "Metric.Name",
    e2sm_kpm_supported_metric_t{
        NO_LABEL,                   // supported label flags (e.g. NO_LABEL, PLMN_ID_LABEL, FIVE_QI_LABEL)
        E2_NODE_LEVEL | UE_LEVEL,   // supported granularity levels
        false,                      // cell-scope granularity supported
        &e2sm_kpm_du_meas_provider_impl::get_my_metric});

Replace e2sm_kpm_du_meas_provider_impl with the actual provider class name from the table above.

The declared labels and levels control which RIC subscription parameters the E2 agent accepts, and they are also advertised to the RIC in the RAN Function Definition at E2 setup. They must not exceed what e2sm_kpm_metric_defs.h defines for this metric name. The constraint is validated by check_e2sm_kpm_metrics_definitions() at startup, which will log an error if a violation is detected.

For contributions that add new metrics, see the Contributing Guide.