Histogram and ODN Loss History
Optical Signal attenuation changes or degrades over time due to environmental, mechanical, or aging factors. This affects the ability of ONTs to receive and transmit signals reliably.
The following table shows possible field scenarios and how the link budget helps troubleshoot issues.
| Field Scenario | Link Budget May Show |
|---|---|
| Low downstream power | Indicates excessive ODN loss or bad optics |
| High upstream power | ONT is hitting the OLT too hard due to low ODN attenuation |
| LOAi/LOSi alarms | Often caused by link budget violations |
| ONT stuck in ranging | Upstream bursts too weak due to high loss |
| GPON/XGS-PON coexistence | Different wavelengths have different budgets |
The test set assists in monitoring signal stability and detecting intermittent loss or degradation. Scroll through time windows to observe loss trends and zoom in on anomalies. The test set applies ITU-T class limits to flag excessive loss. If the loss exceeds the threshold, the ONT may fail to go online or trigger LOSi alarms.
Select the specific wavelength and ODN (Span) loss histogram tabs to monitor Downstream and Upstream signals. Tap the left and right arrows to scroll through the measurement period. The + and – keys zoom in/out of the time axis.
1310/1270 nm Histogram
-
Shows upstream signal strength from ONTs.
-
Can reveal burst inconsistencies or upstream transmission faults.
1310nm Histogram showing Upstream signals
1490/1577 nm Histogram
-
Displays downstream signal strength over time.
1490nm Histogram showing Downstream signals
ODN Loss
Use the ODN Loss histogram to troubleshoot whether poor ONT registration is due to excessive ODN loss or an upstream burst failure.
The ODN Loss shows the difference between the OLT transmit power and the ONT received power at 1490 nm (GPON downstream wavelength). This helps verify that the total optical loss across the ODN (fiber, splitters, connectors) is within the GPON class budget (e.g., B+, C, C+). Refer to OPM Setup.
Exceeding the range will cause the ONT to fail to go online. The ODN link budget and optical power loss calculation need to be planned in advance.
ODN Loss Histogram