OTDR
An Optical Time Domain Reflectometer (OTDR) is a fiber optic measurement device that
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captures real-time data on loss and back reflection across fiber links,
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performs bidirectional analysis by connecting to both transmitter (TX) and receiver (RX) ports, and
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enables assessment and ongoing monitoring of fiber quality and performance.
The NCS 1010 OLT and ILA nodes feature in-built bidirectional OTDR functionality, allowing them to measure loss and back reflection in real time for fiber pairs linked to the TX and RX ports. For the OLT device, the OTDR port can switch between LINE-TX and LINE-RX ports. For the ILA device, the OTDR port can switch among LINE-1-TX, LINE-1-RX, LINE-2-TX, and LINE-2-RX ports.
SOR file
You can view OTDR measurement results in a Standard OTDR Record (SOR) file. The SOR file includes fiber trace details such as distance, reflectance, loss, and fiber attenuation measurements.
You can export the SOR file from NCS 1010 using the command: scp username@device-ip:filename_with_source_location destination-location.
Example:scp test@192.168.0.1:/harddisk:/otdr/ios_OTDR_Ots0_0_0_0_RX_20230301-101927.sor /users/test/
From Release 25.4.1, SOR files from manual and automatic scans are stored in separate folders within the OTDR directory. Automatically
generated SOR files are saved in /harddisk:/otdr/auto/, while manually triggered SOR files are stored in the existing /harddisk:/otdr/ folder.
Benefits
The OTDR offers several key benefits, including:
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Assess the quality of the fiber during system installation, before any live traffic run.
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Monitor the fiber link during operation, including live traffic. You can also monitor the fiber link during troubleshooting after cable cuts or repairs.
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Measure attenuation over the entire fiber link and across individual fiber sections.
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Determine the distance and magnitude of insertion loss and reflection loss.
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Detect fiber events, including concentrated loss events, reflection events, end-of-fiber events, and discontinuities or defects such as pinches or cuts. The OTDR pluggable can also detect loss events from splicing, patch panel connections, and couplers.
OTDR modes
OTDR modes are operational configurations that
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determine how scan parameters (like pulse width and scan duration) are selected and applied,
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optimize measurements for different user needs or fiber types, and
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support both automated and manual control for various operational scenarios.
These modes are designed to address different testing needs and operational preferences:
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Auto: The device automatically selects the optimal values for OTDR pulse width, scan duration, capture start time, and capture end time parameters. This is the default mode and does not require explicit configuration. However, you can manually configure the other scan parameters if needed.
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Expert: You must manually configure all OTDR scan parameters with the valid values that are required for the OTDR measurement. Automatic adjustments are not performed in this mode.
Configure the OTDR scan parameters
Use this procedure to configure the parameters for the OTDR scan. If you do not configure the parameters, the NCS 1010 device uses the default values.
Procedure
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Step 1 |
Enter the OTS controller configuration mode for the port where you want to configure the OTDR parameters. Example:
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Step 2 |
Enter the OTDR mode.
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Step 3 |
Set the required parameters for the OTDR scan. For a complete list of OTDR parameters, refer to OTDR scan parameters. Example:
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Step 4 |
Commit the changes and exit the configuration mode. Example:
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What to do next
Start the OTDR scan manually.OTDR scan parameters
This table provides an overview of key OTDR parameters, including their definitions, measurement units, range of values, and the default values.
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Parameter |
Description |
Unit |
Range |
Default |
|---|---|---|---|---|
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otdr { rx | tx} auto reflectance-threshold <value> |
Threshold beyond which a reflective anomaly is reported as an event in the Rx or Tx direction. |
dB |
–50 to –10 |
–40 |
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otdr { rx | tx} auto splice-loss-threshold <value> |
Threshold beyond which a loss anomaly is reported as an event in Rx or Tx direction. |
dB |
0.2 to 5 |
0.35 |
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otdr { rx | tx} auto excess-reflection-threshold <value> |
Threshold beyond which a reflective event is reported as an excessive reflection event in the Rx or Tx direction. |
dB |
–50 to –10 |
–20 |
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otdr { rx | tx} auto back-scattering <value> |
The back scattering value in the Rx or Tx direction. |
dB |
–90 to –70 |
–81.87 |
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otdr { rx | tx} auto refractive-index <value> |
The refractive-index value in the Rx or Tx direction. |
- |
1.000 to 2.000 |
1.4682 |
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otdr { rx | tx} auto excess-orl-threshold<value> |
Threshold below which OTDR-ABS-ORL-EXCEEDED alarm is reported in the Rx or Tx direction. |
dB |
10–60 |
60 |
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otdr { rx | tx} auto excess-attenuation-threshold<value> |
Threshold beyond which a Non-Reflective event is reported as an excessive attenuation event in the Rx or Tx direction. |
dB |
0.5 to 5 |
5 |
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otdr { rx | tx} auto end-of-fiber-loss-threshold <value> |
Threshold based on which the OTDR identifies the fiber's end, distinguishing it from other components like splices or connectors. |
dB |
5–99 |
5.5 |
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Parameter |
Description |
Unit |
Range |
Default |
|---|---|---|---|---|
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otdr {rx | tx} expert pulse-width <value> |
Pulse width to be used during the expert scan in the Rx or Tx direction. |
ns |
5–20000 |
20 |
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otdr {rx | tx} expert capture-end<value> |
OTDR capture endpoint during the expert scan in the Rx or Tx direction. |
cm |
0–15000000 |
15000000 |
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otdr {rx | tx} expert capture-start <value> |
OTDR capture start point during the expert scan in the Rx or Tx direction |
cm |
0–10000000 |
0 |
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otdr {rx | tx} expert scan duration<value> |
OTDR scan duration during the expert scan in the Rx or Tx direction. |
Seconds |
0–180 |
60 |
View the OTDR measurements
Use this procedure to view the OTDR scan measurement results.
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Feature Name |
Release Information |
Description |
|---|---|---|
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Optical Return Loss Reporting |
Cisco IOS XR Release 7.11.1 |
The Optical Return Loss (ORL) is now calculated during the OTDR scan and displayed as part of the OTDR results. You can also set the ORL threshold value. The ORL represents the total reflected optical power from a complete fiber link while accounting for fiber attenuation. When the ORL falls below a user-configured threshold value, the OTDR-ABS-ORL-EXCEEDED-TX or OTDR-ABS-ORL-EXCEEDED-RX alarm is raised. You can troubleshoot fiber transmission issues using the ORL value and OTDR results. To set the ORL threshold value, these keywords are added to the controller ots command:
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From Release 25.4.1, the OTDR scan measurement results show Total Measured Loss and Total Measured Length.
From Release 7.11.1, Optical Return Loss (ORL) is measured during the OTDR scan and displayed as part of the OTDR results. ORL represents the total reflected optical power from a complete fiber link, while considering the attenuation.
This measurement includes the natural backscattered power of the fiber and the reflected power coming from optical connectors, fiber splicing, or other discontinuities along the link. ORL is expressed with a positive number.
![]() Note |
Higher ORL values are desirable for the fiber because they indicate lower back reflection. For example, an ORL of 40 dB is better than 20 dB. |
Procedure
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Use the command show controllers ots R/S/I/P otdr-info direction to view the OTDR scan measurements. Example:
Example:
After you upgrade the FPD of the line card, you may not be able to view the previous OTDR scan results using the show controllers ots Rack/Slot/Instance/Port otdr-info direction. To access results from earlier OTDR scans, locate the .SOR files on the hard disk. You can dynamically raise or clear Excessive Reflection (ER) and Excess Attenuation (EA) events and alarms by modifying their respective threshold values. In contrast, to raise or clear Fiber End (FE) and Reflectance (R) events, change the relevant thresholds and rerun the OTDR scan. See OTDR scan measurement results for various examples. |

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