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

Signal span loss control

Updated: June 18, 2026

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This section explains how signal span loss control mechanisms set expected thresholds, monitor loss changes, and trigger alarms to enhance optical link reliability.

The signal span loss control is a funtionality that

enables you to set the expected and threshold values for span loss in a link,
monitors changes in the signal span loss in RX direction, and
raises span loss alarms.

Table 1. Feature History
Feature Name	Release Information	Feature Description
MOLS2.0 Signal Span Loss Control Enhancement	Cisco IOS XR Release 25.4.1	The enhanced signal span loss control enables you to set the expected and threshold values for managing RX signal span loss. The enhancement enables the line system to: monitor the change in RX signal span loss value, compare the current and expected RX signal span loss values, check if the span loss difference is within the set threshold values, and raise the relevant alarms, if the span loss difference is more than the threshold values. New CLI parameters added for span-loss attribute on the LINE OTS controller are: rx-expected-span-loss rx-exp-rel-thr-deg <10…420> rx-exp-rel-thr-fail <10...420> To enable the expected RX signal span loss: `rx-expected-span-loss` To disable the expected RX signal span loss: `no span-loss rx-expected-span-loss` Modified YANG models are: Native YANG Model - Cisco-IOS-XR-olc-cfg.yang Open Config model - openconfig-transport-line-common.yang New alarms are introduced: OLC_SPAN_LOSS_FM_RX_SIGNAL_DEGRADE - Rx signal span loss degraded OLC_SPAN_LOSS_FM_RX_SIGNAL_FAIL - Rx signal span loss failed

Note

In R2541, signal span loss control is supported only in the RX direction in the link.

Signal span loss baseline and thresholds

A signal span loss baseline is the currently measured signal span loss value in the optical link that is

stored automatically when you configure the expected span loss during initial setup, and
updated when you reconfigure the expected span loss after fiber repair or link design changes.
used as the reference for evaluating threshold alarms.

Expected signal span loss is the span loss that you find ideal for the network design.

Measured signal span loss refers to the RX signal span loss that is measured immediately after the RX expected span loss is configured for the network.

Signal span loss thresholds

Signal span loss thresholds define the expected degrade and fail ranges. If the measured RX signal span loss falls outside these thresholds, a corresponding alarm is triggered. The two signal span loss thresholds are:

RX signal span loss degrade: Sets the degrade threshold range for the measured RX signal span loss. The threshold range is calculated based on the configured expected signal span loss. When the measured RX signal span loss falls outside of this range, the system triggers the RX signal span loss degrade alarm. The RX signal degrade threshold can be changed with a new expected signal span loss.
RX signal span loss fail: Sets the fail threshold range for the measured RX signal span loss. The threshold range is calculated based on the configured expected signal span loss. When the measured RX signal span loss falls outside of this range, the system triggers the RX signal span loss fail alarm. The RX signal fail threshold can be changed with a new expected signal span loss.

Key characteristics of signal span loss baseline and thresholds

saves the newly measured RX signal span loss as a baseline value each time the expected span loss value is changed.
enables configuration of span loss degrade and fail thresholds on Line OTS controller.
compares the prevailing RX signal span loss and the configured RX expected signal span loss values whenever there is a change in RX signal span loss value.

Note

Initially, the RX expected signal span loss value is set based on the planning tool design or updated to reflect the newly measured span loss after a fiber cut and repair.

Setting expected span loss degrade and fail

In your network,

If RX expected signal span loss is set to 11.0 dB, the system measures the immediate RX signal span loss and saves this value as the baseline.
RX span loss degrade range = RX expected span loss ± RX expected span loss degrade

If RX expected span loss degrade threshold is set to 6.0 dB, the system defines the acceptable degrade range as ±6.0 dB around the expected signal span loss. Therefore, the valid degrade threshold range is from 5.0 to 17.0 dB. If the measured RX signal span loss is more than 5.0 dB and less than 17.0 dB, then there is no degrade alarm. If the measured RX signal span loss falls outside this range, a degrade alarm is triggered.
RX span loss fail range = RX expected span loss ± RX expected span loss fail

If RX expected span loss fail threshold is set to 5.0 dB, the system defines the acceptable fail range as ±5.0 dB around the expected signal span loss. Therefore, the valid fail threshold range is from 6.0 to 16.0 dB. If the measured RX signal span loss is more than 6.0 dB and less than 16.0 dB, then there is no fail alarm. If the measured RX signal span loss falls outside this range, a fail alarm is triggered.

Note

The degrade and fail alarms have a hysteresis of 0.5 dB. For example, if the fail threshold is 5 dB and the alarm is active, the alarm will clear only when the difference between the expected and measured span loss drops below 4.5 dB.

Note

The degrade and fail alarms are mutually exclusive. If the span loss fail threshold is crossed, the degrade alarm is cleared and the fail alarm is raised.

Configure RX signal span loss for MOLS 2.0

This procedure enables you to set the expected and threshold values for RX signal span loss.

Follow these steps to configure the span loss baseline and its thresholds to monitor span loss.

Before you begin

Line system is physically connected, powered on, and its components are provisioned.
Fiber type is provisioned.
Amplifier APC is enabled.

Enter the configuration mode using the configure command.

Procedure

	1.	Enter optical applications configuration mode and select the controller using optical-line-control controller ots R/S/I/P The span loss can be configured only on OTS controller R/S/I/0. Example: `RP/0/RP0/CPU0:ios#configure Mon Sep 18 13:11:53.812 UTC RP/0/RP0/CPU0:ios(config)#optical-line-control controller Ots 0/0/0/0`
	2.	Enable the expected span loss value using span-loss rx-expected-span-loss. Example: `RP/0/RP0/CPU0:ios(config-olc-ots)#span-loss rx-expected-span-loss 65` The RX expected span loss is configured as 6.5 dB and the measured span loss is stored automatically as the baseline.
	3.	Set the degrade and fail threshold values for expected Rx signal span loss. Example: Note By default, span-loss rx-exp-rel-thr-deg and span-loss rx-exp-rel-thr-fail are set to 3.0 and 5.0 dB respectively. `RP/0/RP0/CPU0:ios(config-olc-ots)#span-loss rx-exp-rel-thr-deg 40 RP/0/RP0/CPU0:ios(config-olc-ots)#span-loss rx-exp-rel-thr-fail 60 RP/0/RP0/CPU0:ios(config-olc-ots)#commit` The OTS controller commands consider the inputs to one decimal place for the parameter values. Here, the system sets the span-loss rx-exp-rel-thr-deg as 4.0 dB and `span-loss rx-exp-rel-thr-fail` as 6.0 dB.
	4.	Verify the saved baseline, threshold, and current values using show olc span-loss baseline. Example: `RP/0/RP0/CPU0:ios#show olc span-loss baseline controller ots 0/0/0/0 Controller : Ots0/0/0/0 Neighbour RID : 1.1.1.2 Baseline Timestamp : 2025-06-17 18:00:07 Rx Expected Span Loss Rel Thr Deg : 4.00 dB Rx Expected Span Loss Rel Thr Fail : 6.00 dB Rx Expected Span Loss : 6.50 dB Rx Signal Span Loss : 6.56 dB Rx Calibration Baseline Signal Span Loss : 6.53 dB`
	5.	(Optional) Disable the expected span loss setting. Example: `RP/0/RP0/CPU0:ios(config-olc-ots)# no span-loss rx-expected-span-loss` Disabling this setting clears all outstanding alarms but retains the calibration-baseline-span-loss value.

The system uses the configured threshold values to monitor span loss. Alarms are triggered if loss exceeds the set thresholds.

What to do next

Review alarm status, monitor signal degradation, and adjust baseline values as needed.

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Signal span loss control

Signal span loss baseline and thresholds

Signal span loss thresholds

Key characteristics of signal span loss baseline and thresholds

Setting expected span loss degrade and fail

Configure RX signal span loss for MOLS 2.0

Before you begin

Procedure

Example:

Example:

Example:

Example:

Example:

What to do next