Configuration Guide for Cisco NCS 1001, IOS XR Release 25.x.x

Configure rx-low threshold for PSM

Updated: October 14, 2026

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Use this task to configure the correct rx-low threshold procedure for a PSM working or protected RX port based on manual or automatic amplifier control mode.

Configure the rx-low-threshold before you enable auto-threshold on PSM ports.

The PSM auto-threshold feature monitors the W-RX and P-RX ports of the PSM module for actual received power. When the received power is stable, the feature sets the rx-low-threshold value of the W-RX and P-RX ports to the current power value. The threshold is then set to three dB lower than the received power. If a loss of signal (LOS) occurs at the W-RX or P-RX ports due to a fiber cut or a temporary power disruption, the feature restores the rx-low-threshold value to the configured value.

RP/0/RP0/CPU0:ios#show controllers ots 0/2/0/1
      Parameter Statistics:
      -----------------------
               RX Power = -4.00 dBm
               Rx Low Threshold Current = -7.0 dBm   <<< current value (auto-threshold)

      Configured Parameters:
      -----------------------
               Rx Low Threshold = -38.0 dBm <<< configured value (user configured)

We recommend configuring both the rx-low-threshold and auto-threshold values of the PSM module according to these guidelines:

Procedure

Configure the working rx-low threshold in manual mode. For details about the working rx-low threshold in manual mode, see Configure the working RX-low threshold in manual mode.
Configure the protected rx-low threshold in manual mode. For details about the protected rx-low threshold in manual mode, see Configure the protected RX-low threshold in manual mode.
Configure the working rx-low threshold in automatic mode. For details about the working rx-low threshold in automatic mode, see Configure the working RX-low threshold in automatic mode.
Configure the protected rx-low threshold in automatic mode. For details about the protected rx-low threshold in automatic mode, see Configure the protected RX-low threshold in automatic mode.

The selected PSM port has an RX-low threshold that matches the amplifier control mode and observed power values.

Configure the working rx-low-threshold in manual mode

Configure the rx-low-threshold for the selected PSM port using the value required by the amplifier control mode.

Procedure

Use the show hw-module slot 3 channel-trail-view active command and identify the required power value.

Example:

Channel Trail View - Active - dBm
          ===========================================
                                                                        BST: 0/COM=>1/LINE              PRE: 1/LINE=>0/COM
          Och Name       Wavelength(nm)Freq(GHz) Width(GHz)Rx pwr(dBm) Tx pwr(dBm) Rx pwr(dBm)  Tx pwr(dBm)
          ------------------------------------------------------------------------------------------------------------------------
          Ots-Och0_2_0_0_1  1528.77    196100.0    50.0     -6.10       -4.90       -2.50         6.20
          Ots-Och0_2_0_0_2  1529.16    196050.0    50.0     -5.90       -4.60       -2.20         6.50
          Ots-Och0_2_0_0_3  1529.55    196000.0    50.0     -6.00       -4.80       -2.30         6.30
          Ots-Och0_2_0_0_4  1529.94    195950.0    50.0     -6.10       -4.90       -2.40         6.20
          Ots-Och0_2_0_0_5  1530.33    195900.0    50.0     -6.30       -5.20       -2.60         6.00
          Ots-Och0_2_0_0_6  1530.72    195850.0    50.0     -6.50       -5.30       -2.80         5.90

Examine the PRE: 1/LINE=>0/COM column in the command output and choose the lowest channel Tx pwr value from all the active channels.

Enter the configuration mode.
Example:
```
configure
```

Use the controller ots command to configure the rx-low threshold value.

Example:

controller ots 0/2/0/1 rx-low-threshold 49

Set the threshold value manually to the lowest channel Tx power minus 1 dBm. In this example, channel Ots-Och0_2_0_0_6 is at the lowest Tx power 5.90 dBm. Therefore, the threshold value on the PSM W/RX port is 5.90 minus 1, which equals 4.90 dBm.

If the system works without any grid mode configuration, the channel-trail-view command is not available because channel mapping configuration is not available.

To identify the lowest channel Tx pwr value, use this show command.

show controllers ots0/3/0/0 spectrum-info

Tx power :
       ----------------------------------------------------------------------------------
       spectrum-slice num                        Tx-power values (dBm)
       ----------------------------------------------------------------------------------
         1 - 8               -47.20 -47.20 -47.20 -36.40     -47.20 -47.20 -47.20 -47.20
         9 - 16              -47.20 -47.20 -43.70 -43.70     -47.20 -36.60 -47.20 -43.20
        17 - 24              -47.20 -35.80 -47.20 -47.10     -41.90 -43.20 -42.20 -40.30
        25 - 32              -40.30 -47.20 -41.70 -41.70     -37.50 -47.20 -47.20 -41.90
        33 - 40              -41.90 -47.20 -45.90 -42.10     -42.10 -46.30 -41.60 -39.10
        41 - 48              -41.20 -47.20 -35.80 -45.10     -45.30 -45.30 -40.10 -40.10
        49 - 56              -45.50 -42.60 -45.30 -47.20     -47.20 -40.50 -47.20 -45.80
        57 - 64              -38.60 -40.30 -40.30 -47.20     -47.20 -39.40 -43.10 -43.10
        65 - 72              -42.20 -42.20 -47.20 -47.20     -38.80 -47.20 -47.20 -41.30
        73 - 80              -47.20 -43.00 -40.10 -40.10     -47.20 -36.10 -39.40 -45.70
        81 - 88              -47.20 -41.50 -39.00 -42.50     -47.20 -47.20 -34.30 -47.20
        89 - 96              -47.20 -47.20 -39.90 -39.70     -47.20 -47.20 -47.20 -47.20
        97 - 104             -47.20 -45.10 -39.90 -41.30     -47.20 -39.80 -37.80 -42.00

All the slice power values are expressed in PSD (Power Spectral Density) units of measure [dBm/12.5GHz]. Each slice value is converted to linear mW using the formula 10^(N/10). For example, -20 dBm is equal to 0.01 mW(calculated as 10^(-20/10)), and 0 dBm is equal to 1 mW (calculated as 10^0).

Each slice group that composes a channel is algebraically added to obtain the integral channel power. For example, the first channel of 50 GHz occupies the slice range 1 to 4, and the second channel occupies 5 to 8. The first channel of 75 GHz occupies the slice range 1 to 5 and 6 to 11. The first channel of 100 GHz occupies the slice range 1 to 6 and 7 to 14.

Each channel power that falls below the rx-low-threshold value is excluded from the list of active channels. The channel that has the least value above the rx-low-threshold value is chosen.

Configure the protected rx-low-threshold in manual mode

Configure the rx-low-threshold for the selected PSM port using the value required by the amplifier control mode.

Procedure

Use the show hw-module slot 1 channel-trail-view active command and identify the required power value.

Example:

Channel Trail View - Active - dBm
          ===========================================
                                                                        BST: 0/COM=>1/LINE              PRE: 1/LINE=>0/COM
          Och Name      Wavelength(nm)Freq(GHz) Width(GHz)Rx pwr(dBm) Tx pwr(dBm)  Rx pwr(dBm)  Tx pwr(dBm)
          ------------------------------------------------------------------------------------------------------------------------
          Ots-Och0_2_0_0_1 1528.77    196100.0    50.0     -6.10       -4.90        -2.50         5.00
          Ots-Och0_2_0_0_2 1529.16    196050.0    50.0     -5.90       -4.60        -2.20         5.20
          Ots-Och0_2_0_0_3 1529.55    196000.0    50.0     -6.00       -4.80        -2.30         5.10
          Ots-Och0_2_0_0_4 1529.94    195950.0    50.0     -6.10       -4.90        -2.40         5.00
          Ots-Och0_2_0_0_5 1530.33    195900.0    50.0     -6.30       -5.20        -2.60         5.00
          Ots-Och0_2_0_0_6 1530.72    195850.0    50.0     -6.50       -5.30        -2.80         4.80

Examine the PRE: 1/LINE=>0/COM column in the command output and choose the lowest channel Tx pwr value from all the active channels.

Enter configuration mode.
Example:
```
configure
```
Use the controller ots command to configure the RX-low threshold value.
Example:
```
controller ots 0/2/0/2 rx-low-threshold 38
```
Set the threshold value manually to the lowest channel Tx power minus 1 dBm. In this example, channel Ots-Och0_2_0_0_6 is at the lowest Tx power 4.80 dBm. Therefore, the threshold value on the PSM W/RX port is 4.80 minus 1, which equals 3.80 dBm.

Configure the working rx-low-threshold in automatic mode

Configure the rx-low-threshold for the selected PSM port using the value required by the amplifier control mode.

Procedure

Use the show controllers ots 0/3/0/0 command and identify the required power value.
Example:
```
Configured Parameters:

          -------------------------
                   Ampli Channel power = 0.00 dBm
```
Examine the ampli-channel-power Tx value in the command output.
Enter configuration mode.
Example:
```
configure
```
Use the controller ots command to configure the rx-low-threshold value.
Example:
```
controller ots 0/2/0/1 rx-low-threshold -10
```
Set the threshold value manually to ampli-channel-power minus 1 dBm. In this example, ampli-channel-power Tx value is 0 dBm. Therefore, the threshold value on the PSM W/RX port is 0 minus 1, which equals -1 dBm.

Configure the protected rx-low-threshold in automatic mode

Set the rx-low-threshold for the selected PSM port using the value required by the amplifier control mode.

Procedure

Use the show controllers ots 0/1/0/0 command and identify the required power value.
Example:
```
Configured Parameters:

          -------------------------
                   Ampli Channel power = 2.00 dBm
```
Examine the ampli-channel-power Tx value in the command output.
Enter configuration mode.
Example:
```
configure
```
Use the controller ots command to configure the rx-low-threshold value.
Example:
```
controller ots 0/2/0/2 rx-low-threshold 10
```
Set the threshold value manually to ampli-channel-power minus 1 dBm. In this example, ampli-channel-power Tx value is 2 dBm. Therefore, the threshold value on the PSM W/RX port is 2 minus 1, which equals 1 dBm.

Enable autothreshold for PSM

Before you begin

Configure rx-low-threshold for PSM

Procedure

Use the hw-module location command to enable autothreshold for PSM.

Example:


configure
hw-module location 0/RP0/CPU0 slot 1 psm auto-threshold
commit
end

The configuration is committed and the optical module uses the requested settings.

Configure a relative switch threshold for PSM

A relative switch threshold lets you configure the delta threshold on PSM that triggers the working path to switch to the protected path. You can configure this threshold only if auto-threshold or revertive wtr are not configured.

Procedure

Use the hw-module location command to configure a relative switch threshold for PSM.

Example:


configure terminal
hw-module location 0/RP0/CPU0 slot 1 psm relative-switch-threshold 120 relative-switch-threshold-offset -150
commit
end

The configuration is committed and the optical module uses the requested settings.

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