Configuration Guide for Cisco NCS 1014, IOS XR Releases 26.x.x

ONS-QSFP-OTDR pluggables

Updated: June 18, 2026

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This section explains the function, key attributes, and operational details of ONS-QSFP-OTDR pluggables for fiber network assessment.

The ONS-QSFP-OTDR pluggable is an optical time-domain reflectometer (OTDR) module that

uses a Q-DD form factor and plugs into port 6 of the NCS1K14-EDFA2 line card within the NCS1014 chassis,
enables manual scans to assess and diagnose the condition and performance of an optical fiber network, and
identifies fiber faults and events by sending short optical pulses and measuring the Rayleigh backscatter along the fiber.

Table 1. Feature History
Feature Name	Release Information	Feature Description
ONS-QSFP-OTDR pluggable	Cisco IOS XR Release 25.1.1	The ONS-QSFP-OTDR is a Q-DD form factor module that plugs into port 6 of the NCS1K14-EDFA2 line card, within the NCS1014 Chassis. With this pluggable, you can conduct a manual scan to assess and diagnose the condition and performance of an optical fiber network. CLI commands are: `otdr-start controller ots R/S/I/P {rx\|tx}` `otdr-stop controller ots R/S/I/P {rx\|tx}`

An ONS-QSFP-OTDR pluggable is designed for use with the EDFA2 card and provides real-time measurements of loss and back reflection for the fiber pair connected to the TX and 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.

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

ONS-QSFP-OTDR pluggables offer several benefits:

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.

Limitations

The ONS-QSFP-OTDR pluggable has these limitations:

The OTDR scan feature is supported only on the LINE OTS controller.
Scans are conducted separately for the OTS controller in the RX direction or TX direction.

OTDR modes

In NCS 1014, OTDR works in two modes:

Auto
Expert

Auto mode

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.

Expert mode

You must manually configure all OTDR scan parameters with the required valid values for measurement. Automatic adjustments are not performed in this mode.

Configure the OTDR scan parameters for auto and expert modes

Follow these steps to configure the various parameters for the OTDR scan. If you do not configure the OTDR scan parameters, the NCS 1014 device uses the default values for OTDR scan parameters.

Procedure

Enter the OTS controller configuration mode for the port on which 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

Enter the OTDR mode.


If you want to configure the	then run the command
Expert mode	`RP/0/RP0/CPU0:ios(config-Ots)#otdr scan-mode expert`
Auto mode	Auto mode is the default and does not require explicit configuration.

Set the required parameters for the OTDR scan. See OTDR scan parameters for auto and expert modes for the complete list of OTDR parameters, commit, and exit the configuration.

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 0.2
RP/0/RP0/CPU0:ios(config-Ots)#otdr rx expert pulse-width 6000
RP/0/RP0/CPU0:ios(config-Ots)#commit
RP/0/RP0/CPU0:ios(config-Ots)#exit
RP/0/RP0/CPU0:ios(config)#exit

OTDR scan parameters for auto and expert modes

This table provides an overview of key OTDR parameters, including their definitions, measurement units, range of values and the default values for Auto and Expert modes.

Table 2. **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 –23	–23
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 to 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 99	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	0.5 to 31.0	5.0

Table 3. **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	8 to 50000	20000
otdr {rx \| tx} expert capture-end<value>	OTDR capture endpoint during the expert scan in the Rx or Tx direction.	cm	0 to 11900000	11900000
otdr {rx \| tx} expert capture-start <value>	OTDR capture start point during expert scan in the Rx or Tx direction	cm	0 to 11900000	0
otdr {rx \| tx} expert scan duration<value>	OTDR scan duration during expert scan in the Rx or Tx direction.	seconds	0 to 360	180

OTDR negotiations

An OTDR negotiation is a network coordination process that

uses a message-based handshake between two adjacent network nodes equipped with OTDR devices,
ensures that only one node may initiate an OTDR scan at a time to prevent simultaneous scans on the same fiber, and
helps avoid measurement conflicts to ensure accurate scan results.

You can use force option in the command otdr-start controller ots R/S/I/P to bypass negotiation during the OTDR scan process.

Table 4. Feature History
Feature Name	Release Information	Feature Description
OTDR negotiation	Cisco IOS XR Release 25.2.1	The OTDR scan process has been enhanced to include negotiation with a remote peer before initiating the scan. This negotiation helps prevent simultaneous scans on the same fiber, thereby avoiding measurement conflicts and ensuring accurate scan results. The force option can be used to start a scan without negotiation. However, it should be used carefully to avoid simultaneous scans between the near-end and far-end nodes on the same fiber. Command modified: The keyword force has been added to the otdr-start controller ots R/S/I/P direction command.

Advantage

OTDR negotiations help prevent simultaneous scans on the same fiber, thereby avoiding measurement conflicts and ensuring accurate scan results.

How OTDR negotiation works

To ensure an efficient and conflict-free OTDR scan process, the local node follows these steps:

Before starting any OTDR scan, the local node checks if the fiber is available for scanning.
The local node verifies whether there is an ongoing scan from the remote node.
If no scan is currently running on the fiber, the local node requests a remote span reservation.
If the remote node acknowledges the remote span reservation, the local node initiates the scan.

This process prevents conflicts between peer node scans.

Note

If the link between the nodes is down or OSC pluggable is missing, the negotiation cannot occur, and the scan request will fail. In this scenario, you can still initiate an OTDR scan without negotiation. See Start the OTDR scan manually.

Start the OTDR scan manually

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

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.

Before you begin

Perform the patch cord connection check before starting the manual scan.

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 0/3/0/0 tx Tue Jan 7 04:14:13.712 UTC OTS OTDR Scan Started at TX RP/0/RP0/CPU0:ios#otdr-start controller ots 0/3/0/0 rx Tue Jan 7 04:33:33.326 UTC OTS OTDR Scan Started at RX`
	2.	Use the `force` keyword, to run the manual OTDR scan operation without negotiating with the peer or when the communication channel is not up. Example: `RP/0/RP0/CPU0:ios#otdr-start controller ots 0/0/0/0 rx force Wed Sep 4 08:78:34.186 UTC OTS OTDR Scan Started at RX RP/0/RP0/CPU0:ios#` The forced otdr-start command can fail immediately if the OTDR is already performing a scan on any of the four possible spans associated with the ports (0-TX, 0-RX, 2-TX, 2-RX). In such cases, this error message may appear: OTDR Scan cannot be started as another scan is in progress. To resolve this issue, wait before attempting to restart the OTDR scan until the ongoing scan is complete.
	3.	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_nodename_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 is initiated manually on the selected direction. If a scan is already in progress, wait for it to finish before restarting.

What to do next

Review the OTDR scan results to verify fiber integrity or detect anomalies.
If any issues are identified, take corrective action.

View the OTDR measurements

Use this procedure to view the OTDR scan measurement results.

From Release 25.4.1, the OTDR scan measures Total Measured Loss and Total Measured Length and displays them as part of the OTDR results.

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 0/3/0/0 otdr-info rx
Tue Jan  7 04:37:46.711 UTC
Scan Direction: RX
Scan Status: Data Ready
Optical Return Loss: -90.6 dB
SOR file: /harddisk:/otdr/R1_OTDR_Ots0_3_0_0_RX_20250107-043559.sor
Total Events detected: 1
Scan Timestamp: Tue Jan  7 04:33:33 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 FE                   |  11.9100         |  34.44           |  5.53            |  0.30

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#sh controllers ots 0/3/0/0 otdr-info tx
Thu Aug 21 07:18:27.272 UTC
        Scan Direction: TX
        Scan Status: Data Ready
        Total Measured Loss: 12.05 dB
        Total Measured Length: 1664.3300 m
        Optical Return Loss: 90.0 dB
        SOR file: /harddisk:/otdr/Site1.ABC_xyz-1_ios_Ots0_3_0_0_TX_20250821-070722.sor
        Total Events detected: 7
        Scan Timestamp: Thu Aug 21 07:07:22 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                      |  280.2100        |  5.74            |  0.37            |  0.30
        2           |  NR                      |  353.6900        |  5.74            |  0.42            |  0.30
        3           |  NR                      |  994.0800        |  34.44           |  0.77            |  0.30
        4           |  NR                      |  1106.7600       |  34.44           |  0.41            |  0.30
        5           |  NR                      |  1246.1600       |  34.44           |  1.42            |  0.30
        6           |  NR                      |  1440.9600       |  34.44           |  1.42            |  0.30
        7           |  NR FE                   |  1664.3300       |  34.44           |  2.08            |  0.30

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.

Note

The configured OTDR expert pulse-width value is accurately written to the hardware registers. However, due to the granularity of the hardware, the value may be rounded. This rounding can lead to differences between the provisioned values and the values displayed in the SOR file.

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 status for a list of the different OTDR scan statuses and their definitions.

Stop the OTDR scan

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#

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