Configuration Guide for Cisco Optical Site Manager, IOS XR Release 26.x.x

PSM card protection mechanism

Updated: October 14, 2026

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This section explains pSM card protection mechanism, including key behavior and operational context that help you understand when to use the feature in Cisco Optical Site Manager.

PSM card protection switching is a high-availability mechanism that automatically transfers optical traffic from a primary Protection Switching Module (PSM) card to a redundant standby PSM card in the event of a failure or degradation of the active card.

It provides automatic failover, ensuring continuous operation and minimizing service interruption.
It enhances the overall reliability and uptime of the optical transport network.
It is typically implemented in one-plus-one or one-to-one protection schemes to maintain optical signal integrity.

Types of Protection Switching

The PSM card supports the following types of protection switching:

Revertive Protection Switching: Traffic automatically returns to the working path from the protection path once the fiber issue is resolved and the Loss of Signal (LOS) alarm is cleared on the working path.
Non-Revertive Protection Switching: Once traffic is switched to the protection path due to a signal failure, it remains on the protection path even after the failure on the working path is resolved.

Enable the revertive protection switching

Protection switching offers a safeguard against optical fiber faults. When a failure is detected, the system automatically switches live traffic from the working path to the protection path. This process ensures uninterrupted data transmission.

Revertive switching is one of the two protection switching modes. In non-revertive mode, traffic remains on the protection path even after the working path is restored. The revertive mode includes a configurable Wait to Restore (WTR) timer that delays the switch back to the working path to ensure stability.

Before you begin

Follow these steps to enable revertive protection switching on the PSM card:

Procedure

Click the Maintenance tab.
Click the Protection section to expand it.
Click the Edit button.

The fields in the table become editable.
Select true from the drop-down list under the Revertive column.
Specify the time in seconds under the Wait to Restore column.

Wait to Restore (WTR) is the time delay (in seconds) applied after a Loss of Signal (LOS) alarm on the working path is cleared. Once the WTR timer expires, traffic is switched back to the working path.
Click Apply.

Revertive protection switching is enabled on the card.

Revertive protection switching automatically switches traffic back to the working path after the fault is cleared and the WTR timer expires. This process minimizes service disruption and optimizes network performance.

What to do next

Configure the non-revertive protection switching

Non-revertive protection switching ensures that, once traffic is switched to the protection path due to a signal failure, it remains there even after the failure on the working path is cleared.

Non-revertive switching contrasts with revertive switching, where traffic automatically returns to the working path after fault resolution. Non-revertive mode is often used to maintain traffic on the protection path until a manual switch is performed or other conditions are met. It is also applicable in MPLS-TE path protection and EVPN configurations to control failover behavior.

Before you begin

Follow these steps to enable or disable non-revertive protection switching on a PSM card interface:

Procedure

Click the Maintenance tab.
Click the Protection section to expand it.
Select the check-box corresponding to the PSM switch and then click Protection Switch button.

The New Switch Command dialog box is displayed.
Complete these steps to enable non-revertive switching in the New Switch Command dialog box:
1. Select the interface you want to lockout from the Target Interface drop-down list.
2. Select Lock-Out from the Switch Command drop-down list.
3. Click Apply.
Complete these steps to disable non-revertive switching:
1. Select Release from the Switch Command drop-down list.
2. Click Apply.

Traffic remains on the protection path after a failure is cleared. This behavior avoids potential disruptions that can result from switching paths repeatedly. When non-revertive mode is disabled, traffic reverts automatically to the original working path once it is restored.

Perform a manual switch

A manual switch lets you transfer traffic between the working and protection paths. Typically, this switch is used during scheduled maintenance or when manual intervention is necessary.

Before you begin

Follow these steps to perform a manual switch:

Procedure

Click the Maintenance tab.
Click the Protection section to expand it.
Select the check-box corresponding to the PSM switch and then click Protection Switch button.

The New Switch Command dialog box is displayed.
Select the interface you want to manually switch to from the Target Interface drop-down list.
Select Manual-Switch from the Switch Command drop-down list.
Click Apply.

The system status shows the manual switch state and confirms that the traffic is switched.

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