Cisco NCS 1010 Optical Applications Configuration Guide, IOS XR Release 25.x.x

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Fiber link monitoring and diagnostics using OTDR

Updated: February 5, 2026

Overview

This topic explains how Optical Time Domain Reflectometers (OTDRs) are used for real-time monitoring and diagnostics of fiber optic links, highlighting their ability to measure loss, reflectance, and detect defects to ensure optimal fiber network performance.

An Optical Time Domain Reflectometer (OTDR) is a fiber optic measurement device that

  • captures real-time data on loss and back reflection across fiber links,

  • performs bidirectional analysis by connecting to both transmitter (TX) and receiver (RX) ports, and

  • 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:

  • Assess the quality of the fiber during system installation, before any live traffic run.

  • Monitor the fiber link during operation, including live traffic. You can also monitor the fiber link during troubleshooting after cable cuts or repairs.

  • Measure attenuation over the entire fiber link and across individual fiber sections.

  • Determine the distance and magnitude of insertion loss and reflection loss.

  • 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

  • determine how scan parameters (like pulse width and scan duration) are selected and applied,

  • optimize measurements for different user needs or fiber types, and

  • support both automated and manual control for various operational scenarios.

An OTDR can operate in several modes to suit different network testing requirements. Selecting the appropriate mode helps ensure efficient, accurate fiber characterization by adapting OTDR performance to the specific task or fiber segment.

These modes are designed to address different testing needs and operational preferences:

  1. 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.

  2. 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

1.

Enter the OTS controller configuration mode for the port where you want to configure the OTDR parameters.

Example:

RP/0/RP0/CPU0:ios#config 
RP/0/RP0/CPU0:ios(config)#controller ots 0/0/0/0
2.

Enter the OTDR mode.

If you want to configure the then run this command

Expert mode

 
RP/0/RP0/CPU0:ios(config-Ots)#otdr scan-mode expert

Auto mode

Auto mode is the default and you do not need to configure it
3.

Set the required parameters for the OTDR scan. For a complete list of OTDR parameters, refer to OTDR scan parameters.

Example:


RP/0/RP0/CPU0:ios(config-Ots)#otdr rx auto reflectance-threshold -50
RP/0/RP0/CPU0:ios(config-Ots)#otdr rx auto splice-loss-threshold 200
RP/0/RP0/CPU0:ios(config-Ots)#otdr rx expert pulse-width 6000
RP/0/RP0/CPU0:ios(config-Ots)#commit
4.

Commit the changes and exit the configuration mode.

Example:

RP/0/RP0/CPU0:ios(config)#commit
RP/0/RP0/CPU0:ios(config)#exit

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.

Table 1. OTDR scan parameters in Auto mode
Parameter Description Unit Range Default

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

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

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

otdr { rx | tx} auto back-scattering <value>

The back scattering value in the Rx or Tx direction.

dB

–90 to –70

–81.87

otdr { rx | tx} auto refractive-index <value>

The refractive-index value in the Rx or Tx direction.

-

1.000 to 2.000

1.4682

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

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

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
Table 2. OTDR scan parameters in Expert mode
Parameter Description Unit Range Default

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

otdr {rx | tx} expert capture-end<value>

OTDR capture endpoint during the expert scan in the Rx or Tx direction.

cm

0–15000000

15000000

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

otdr {rx | tx} expert scan duration<value>

OTDR scan duration during the expert scan in the Rx or Tx direction.

Seconds

0–180

60

Start the OTDR scan manually

Manually initiate the OTDR scan to diagnose fiber defects, check fiber quality, or verify proper installation.

Note

The Raman tuning application locks the OTDR scan at both fiber ends before the tuning starts, and releases the lock after the tuning completes. Therefore, when you try to start the OTDR scan when Raman tuning is running, your request gets rejected.

From Release 25.4.1, you can use the label keyword to append a custom substring as a prefix to the SOR file name. This substring helps you identify and retrieve specific SOR files stored in the directory.

Procedure

1.

Use the otdr-start controller ots R/S/I/P direction to start the OTDR scan manually.

Example:

RP/0/RP0/CPU0:ios#otdr-start controller ots 0/0/0/0 rx 
Wed Feb  9 05:49:39.178 UTC
OTS OTDR Scan Started at RX
RP/0/RP0/CPU0:ios#

This example illustrates a rejected OTDR start request. Once an OTDR scan request has been rejected, it will not automatically run after the lock is released. You will need to create a new request to start the OTDR scan again. These examples show that OTDR scan is locked by Raman tuning:

RP/0/RP0/CPU0:ios#otdr-start controller ots 0/0/0/0 rx
Tue Feb 28 10:25:43.379 UTC
OTDR Scan cannot be started as it is locked by Another Entity/Application.
RP/0/RP0/CPU0:ios#
2.

Use the label string keyword, to append a custom substring as a prefix to the SOR file name.

Example:

RP/0/RP0/CPU0:ios#otdr-start controller ots 0/0/0/0 rx label Site1.ABC_xyz-1
Mon Nov 3 09:56:23.278 UTC
OTS OTDR Scan Started at RX
RP/0/RP0/CPU0:ios#

This example appends the string Site1.ABC_xyz-1 to the SOR file name. For example: /harddisk:/otdr/Site1.ABC_xyz-1_ios _OTDR_Ots0_0_0_0_RX_20250306-110133.sor.

The OTDR label must adhere to these limitations: Only the special characters dot, hyphen, and underscore are permitted. The maximum file name length is 255 characters. The maximum label length is 55 characters.

The OTDR scan initiates and begins analyzing the fiber. If the scan cannot start, an error message states the reason.

What to do next

Review scan results to identify defects and assess fiber quality.

View the OTDR measurements

Use this procedure to view the OTDR scan measurement results.

Table 1. Feature History
Feature Name Release Information Description

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:

  • otdr rx auto excess-orl-threshold value

  • otdr tx auto excess-orl-threshold value

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

Use the command show controllers ots R/S/I/P otdr-info direction to view the OTDR scan measurements.

Example:

RP/0/RP0/CPU0:ios#show controllers ots 0/0/0/0 otdr-info rx 
Wed Feb  9 05:55:19.791 UTC
       Scan Direction: RX
       Scan Status: Data Ready 
       SOR file: /harddisk:/otdr/IOS_NCS1010_OTDR_Ots0_0_0_0_RX_20220209-055045.sor
       Total Events detected: 11 
       Scan Timestamp: Wed Feb  9 05:50:45 2022 UTC
       Event Type Legend:  NR:Non-Reflective  R:Reflective  FE:Fiber-End  ER:Excess-Reflection
      Event#  | Detected Event(s) | Location(km) | Accuracy(m) | Magnitude(dB)| Attenuation/km(dB)
      1       | R                 | 50.4709      | 52.47       | -39.87       |  0.18            
      2       | NR                | 50.4709      | 52.47       | 1.17         |  0.18            
      3       | R                 | 100.9261     | 102.92      | -37.73       |  0.21            
      4       | NR                | 100.9261     | 102.92      | 1.01         |  0.21            
      5       | R                 | 105.9500     | 107.94      | -38.52       |  0.24            
      6       | NR                | 105.9500     | 107.94      | 0.85         |  0.24            
      7       | R                 | 112.7458     | 114.74      | -40.56       |  0.00             
      8       | NR                | 112.7458     | 114.74      | 1.48         |  0.00            
      9       | NR                | 117.9873     | 119.98      | 0.66         |  -0.02           
      10      | R FE              | 120.1206     | 122.12      | -35.55       |  0.00            
      11      | NR FE             | 120.1206     | 122.12      | 21.65        |  0.00

Example:

These are the sample OTDR measurement results displaying Total Measured Loss, Total Measured Length and SOR file with appended OTDR label. 
RP/0/RP0/CPU0:ios#show controllers ots 0/0/0/2 otdr-info tx
Thu Dec  4 09:28:25.136 IST
        Scan Direction: TX
        Scan Status: Data Ready 
        Total Measured Loss: 11.04 dB
        Total Measured Length: 50746.3000 m
        Optical Return Loss: 25.0 dB
        SOR file: /harddisk:/otdr/auto/ios_OTDR_Ots0_0_0_2_TX_20251203-122210.sor
        Total Events detected: 4
        Scan Timestamp: Wed Dec  3 12:22:10 2025 UTC
        Event Type Legend:  NR:Non-Reflective  R:Reflective  FE:Fiber-End  ER:Excess-Reflection EA:Excess-Attenuation

        Event#      |  Detected Event(s)       |  Location(m)     |  Accuracy(m)     |  Magnitude(dB)   |  Attenuation/km(dB)
        1           |  NR                      |  0.6800          |  2.00            |  0.66            |  0.00            
        2           |  R                       |  10.4800         |  2.01            |  -33.66          |  0.00            
        3           |  R FE ER                 |  50746.3000      |  52.74           |  -15.28          |  0.20            
        4           |  NR FE                   |  50746.3000      |  52.74           |  11.04           |  0.20
Note

The output shows Total measured loss and Total measured length only if a Fiber-End (FE) event is detected.

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.

OTDR scan measurement results

This sample displays the ORL value as part of OTDR status:

RP/0/RP0/CPU0:ios#show controllers Ots 0/0/0/2 otdr-info rx
Mon Oct 2 11:55:48.552 UTC
Scan Direction: RX
Scan Status: Data Ready 
Optical Return Loss: 39.0 dB
SOR file: /harddisk:/otdr/ios_OTDR_Ots0_0_0_2_RX_20231001-110754.sor
Total Events detected: 8
Scan Timestamp: Sun Oct  1 11:07:54 2023 UTC
Event Type Legend:NR:Non-Reflective R:Reflective FE:Fiber-End ER:Excess-Reflection EA:Excess-Attenuation
Event# | Detected Event(s) | Location(m) | Accuracy(m) | Magnitude(dB)| Attenuation/km(dB)
1      | NR EA             | 4.4100      | 2.00        | 0.69         | 0.00 
2      | NR                | 664.3200    | 2.66        | 0.21         | 0.00 
3      | R ER              | 18222.3900  | 20.22       | -33.78       | 0.19 
4      | NR                | 18222.3900  | 20.22       | 0.35         | 0.19 
5      | R ER              | 68674.4800  | 70.67       | -32.25       | 0.20 
6      | NR                | 68674.4800  | 70.67       |  0.36        | 0.20 
7      | R FE ER           | 118765.2600 | 120.76      | -28.55       | 0.23
8      | NR FE             | 118765.2600 | 120.76      | 25.86        | 0.23

Stop the OTDR scan manually

Use this procedure to stop the OTDR scan manually.

Procedure

Enter the command otdr-stop controller ots R/S/I/P direction to stop the OTDR scan.

Example:

RP/0/RP0/CPU0:ios#otdr-stop controller ots 0/0/0/0 rx 
Wed Feb  9 06:03:37.406 UTC
OTS OTDR Scan Stopped at RX
RP/0/RP0/CPU0:ios#