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

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Operation of span-mode APC

Updated: February 5, 2026

Overview

This topic explains how span-mode APC operates in optical networks, detailing its decentralized automatic power control mechanism, key operational behaviors, and restrictions compared to centralized APC. It also covers relevant alarm conditions and configuration guidelines for effective deployment.

Starting with R7.11.1, you can configure APC in span-mode. span-mode APC is a decentralized automatic power control method used in optical networks, where each node independently adjusts its power levels based on changes in span loss.

If there is a discrepancy in the network without any change in span-loss, instead of triggering APC regulation, the system raises the corresponding alarm. For centralized APC, the power correction threshold is 0.7 dB. The threshold for span-mode APC is 0.5 dB.

Unlike centralized power control mode, where the manager node controls power adjustments across the network, each node in span-mode adjusts its own power based on the conditions of its direct connections or spans. There are no APC manager nodes in span-mode. Regulation in span-mode APC takes place when a node detects a change in Rx span loss. Span-mode APC does not perform regulation when there is a change in Rx power as a result of other changes. There are two exceptions to this:

  • Span-mode APC compensates for power changes in the channels that an OLT receives on the ADD ports.

  • Span-mode APC performs power correction when you change the DROP PSD configuration

When a node is unable to compensate for changes that require power correction, it raises the OOR (Out-of-Range) alarm and informs the receiving node of the discrepancy. The receiving node then performs power correction to address the issue.

If there is a power change in the network due to another cause, APC does not perform power correction. However, APC raises the APC-TARGET-PSD-NOT-MET alarm after a configured interval. You can investigate the cause of the change in the network and fix the issues.

APC behavior before R7.11.1 is Centralized APC.

Restrictions for span-mode APC

  • Do not delete channels when APC is in span mode.

  • Do not disable or enable APC, link tuner, or gain estimator after the ALC process is complete and span-mode APC is active.

  • Do not initiate gain estimator application using exec CLI after ALC process is complete and span-mode APC is active.

  • You must configure channel maps on all ILA nodes. Use hw-module location 0/0/NXR0 grid-mode flex [inline-ampli | terminal-ampli] channel-id id centre-freq frequency width width command to configure the channel map for all 32 channels.

  • You must pause span-mode APC before deleting or creating cross-connects.

Configure APC in span mode

Use this procedure to configure APC in span mode on OLT node and ILA node.

Procedure

1.

Use these commands to configure APC in span mode on an OLT node.

Example:


RP/0/RP0/CPU0:ios#configure
RP/0/RP0/CPU0:ios(config)#optical-line-control
RP/0/RP0/CPU0:ios(config-olc)#controller ots 0/0/0/0
RP/0/RP0/CPU0:ios(config-olc-ots)#apc-span-mode RX
RP/0/RP0/CPU0:ios(config-olc-ots)#apc-span-mode TX
RP/0/RP0/CPU0:ios(config-olc-ots)#commit
RP/0/RP0/CPU0:ios(config-olc-ots)#end
2.

Use these commands to configure APC in span mode on an ILA node.

Example:


RP/0/RP0/CPU0:ios#configure
RP/0/RP0/CPU0:ios(config)#optical-line-control
RP/0/RP0/CPU0:ios(config-olc)#controller ots 0/0/0/0
RP/0/RP0/CPU0:ios(config-olc-ots)#apc-span-mode TX
RP/0/RP0/CPU0:ios(config-olc-ots)#commit
RP/0/RP0/CPU0:ios(config-olc-ots)#end

APC operates in centralized mode during automatic link calibration. After ALC completes, it saves a system baseline. If span mode configurations are present, ALC switches APC mode to span mode.

Pause APC in span mode

Use this procedure to pause APC in span mode.

Procedure

Use these commands to pause APC in span mode.

Example:


RP/0/RP0/CPU0:ios#configure
RP/0/RP0/CPU0:ios(config)#optical-line-control
RP/0/RP0/CPU0:ios(config-olc)#controller ots 0/0/0/0
RP/0/RP0/CPU0:ios(config-olc-ots)#apc-span-mode-pause tx 
RP/0/RP0/CPU0:ios(config-olc-ots)#commit
RP/0/RP0/CPU0:ios(config-olc-ots)#end