Optical power monitoring: the leading indicator FTTH ISPs still under-use

Every ONU on the planet reports its optical transmit and receive power to the OLT. Every operator has the data. Almost no operator uses it as a leading indicator. This is a short study of why that is, and what changes when it is instrumented properly.

The underlying specifications are well-established: [ITU-T G.988](https://www.itu.int/rec/T-REC-G.988/en) defines the OMCI management information base, including the ANI-G (ANI-Generic) managed entity that exposes optical parameters. Every compliant ONU exposes Tx/Rx power in dBm through OMCI, which the OLT then makes available upward through SNMP, gNMI or the vendor's NMS API.

Why the data is under-used

Three reasons: (1) most NMS tools poll at 5- or 15-minute intervals, which is far coarser than optical drift needs; (2) very few tools retain per-ONU historical baselines, so operators have no reference against which "1 dB degradation" means anything; (3) the alarm rules are usually generic thresholds, not per-unit baseline offsets.

What "instrumented properly" means

1. 1Per-ONU sampling every 60 seconds during business hours, at 5 minutes off-hours.
2. 2Per-ONU installation baseline captured at ONT authorisation time; re-baseline on a physical work-order that touches the fibre.
3. 3Alarm rule: 2 dB drift from baseline, sustained across 5 samples. Not "Rx power below −25 dBm" in the abstract.
4. 4Correlate with weather + temperature at the OLT site; humidity and freeze-thaw drive most seasonal drift.

The operational payoff

Splices degrade slowly. A typical outdoor splice failure looks like: month 1 baseline, month 4 begin drift, month 6 threshold cross, month 7 hard failure. Two-to-three months of warning is the norm, not the exception. Netxol NMM captures per-ONU history by default; see [Netxol NMM](/products/modules/nmm) and the [OLT management solution](/solutions/olt-management).

A note on vendor differences

OMCI exposes the primitive; how OLT vendors surface it upward varies. Huawei via MA5800 exposes it well through the U2000 API; ZTE C620 has slightly different attribute paths; FiberHome depends on OLT firmware version. A vendor-neutral abstraction (Netxol's or otherwise) collapses this — for the vendor-abstraction detail see the [multi-vendor OLT / GPON scaling study](/blog/multi-vendor-gpon-scaling-study).