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

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

FEC

Updated: June 18, 2026

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This section explains how forward error correction methods add redundancy during data transmission, enabling receivers to detect and correct transmission errors without retransmission.

Forward Error Correction (FEC) is a method for controlling errors during data transmission that:

  • adds data redundancy to the transmitted message using an algorithm, and

  • enables the receiver to detect and correct a limited number of errors occurring anywhere in the message, thereby eliminating the need for the transmitter to resend the message.

This feature can be enabled on 1.2T and 2.4T cards. FEC is automatically enabled on the pluggables installed in the NCS 1014.

Note

When you upgrade the software of an NCS 1014 with pluggables in the FEC disabled mode, traffic is affected.

FEC states for CoherentDSP controller

This table lists the FEC states for the coherentDSP controllers.

Table 1. FEC state for CoherentDSP controllers

State

Description

EnhancedSD15

FEC Soft-Decision 15. (Default)

Q-Margin support

Q-margin is an important optical parameter that characterizes the health of an optical link. The Q-margin value is calculated based on the average bit error rate (BER) in the optical link.

Enhanced Q-Margin support

Enhanced Q-Margin is supported for Forward Error Correction (FEC) and Performance Monitoring on CoherentDSP controllers for 2.4T cards. Enhanced Q-margin provides a better error free signal in the optical link. The enhanced Q-margin value is calculated based on the maximum number of errors per frame.

An attribute that is called instantaneous Q-margin is displayed in the output of the show controllers coherentDSP command. The lower the delta value between the instantaneous Q-margin value with the Q-margin value, the better the FEC performance of the NCS 1014 system.

The instantaneous Q-margin values thus help you to optimize the system with continuous error correction in subsea transport networks.

Configure FEC on the Ethernet controller

Use this task to configure FEC on the CoherentDSP controller.

Procedure

Run the controller { HundredGigECtrlr | fourHundredGigECtrlr } R/S/I/P fec { none | standard } command.

Example:

This sample shows how to configure FEC on the Ethernet controller. 


RP/0/RP0/CPU0:ios#configure
RP/0/RP0/CPU0:ios(config)#controller HundredGigECtrlr 0/1/0/6/ fec standard
RP/0/RP0/CPU0:ios(config)#commit

This sample shows the running FEC configuration on the Ethernet controller.


RP/0/RP0/CPU0:BH-SIT2#show controller HundredGigECtrlr 0/1/0/6
Tue Jul 16 15:30:30.165 IST
Operational data for interface HundredGigECtrlr0/1/0/6/2:

State:
    Administrative state: enabled
    Operational state: Down (Reason: State undefined)
    LED state: Red On
    Maintenance: Disabled
    AINS Soak: None
      Total Duration: 0 hour(s) 0 minute(s)
      Remaining Duration: 0 hour(s) 0 minute(s) 0 second(s)
    Laser Squelch: Disabled

Phy:
    Media type: Not known
    Alarms:
        Current:
            Loss of Frequency Sync Data
    Statistics:
        FEC:
            Corrected Codeword Count: 0
            Uncorrected Codeword Count: 0
Autonegotiation disabled.
Operational values:
    Speed: 100Gbps
    Duplex: Full Duplex
    Flowcontrol: None
    Loopback: None (or external)
    BER monitoring:
        Not supported
    Forward error correction: Standard (Reed-Solomon)
    Holdoff Time: 0ms

From Release 24.2.11, the show controllers command output displays post FEC BER and pre FEC BER for the Ethernet controllers of the 2.4T and 2.4TX cards.


RP/0/RP0/CPU0:ios#show controllers fourHundredGigEctrlr 0/1/0/2
Thu Jan 18 18:58:03.846 UTC
Operational data for interface FourHundredGigECtrlr0/1/0/2:
State:
    Administrative state: enabled
    Operational state: Up
    LED state: Green On
    Maintenance: Disabled
    AINS Soak: None
      Total Duration: 0 hour(s) 0 minute(s)
      Remaining Duration: 0 hour(s) 0 minute(s) 0 second(s)
    Laser Squelch: Disabled
    Insert Idle Ingress: Disabled
    Insert Idle Egress: Disabled
Phy:
    Media type: Not known
    Statistics:
        FEC:
            Corrected Codeword Count: 358543                   Valid: True       Start time: 18:54:03 Thu Jan 18 2024
            Uncorrected Codeword Count: 0                      Valid: True       Start time: 18:54:03 Thu Jan 18 2024
        PCS:
            Total BIP errors: 0                                Valid: True       Start time: 18:54:03 Thu Jan 18 2024
            Total frame errors: 0                              Valid: False      Start time: 18:54:03 Thu Jan 18 2024
            Total Bad SH: 0                                    Valid: False      Start time: 18:54:03 Thu Jan 18 2024
Autonegotiation disabled.
Operational values:
    Speed: 400Gbps
    Duplex: Full Duplex
    Flowcontrol: None
    Loopback: None (or external)
    Pre FEC BER: 9.1E-10
    Post FEC BER: 0.0E+00
    BER monitoring:
        Not supported
    Forward error correction: Standard (Reed-Solomon)
    Holdoff Time: 0ms

Configure FEC on CoherentDSP controllers

Use this task to configure FEC on the CoherentDSP controller.

Procedure

Run the controller coherentDSP R/S/I/P fec {EnhancedSD15} command.

Example:

This sample shows how to configure FEC on the CoherentDSP controller.


RP/0/RP0/CPU0:ios#configure
RP/0/RP0/CPU0:ios(config)#controller coherentDSP 0/0/0/0
RP/0/RP0/CPU0:ios(config-CoDSP)#fec EnhancedSD15
Tue Feb 25 11:25:52.670 UTC
WARNING! Changing FEC mode can impact traffic
RP/0/RP0/CPU0:ios(config-CoDSP)#commit

Verify FEC on CoherentDSP controllers

This sample shows the FEC configuration on the CoherentDSP controller.


RP/0/RP0/CPU0:ios#show controllers coherentDSP 0/0/0/0                                                                                    
Tue Feb 25 11:26:08.235 UTC                                                                                                                                    

Port                                            : CoherentDSP 0/0/0/0
Controller State                                : Up                 
Inherited Secondary State                       : Normal             
Configured Secondary State                      : Normal             
Derived State                                   : In Service         
Loopback mode                                   : None               
BER Thresholds                                  : SF = 1.0E-5  SD = 1.0E-7
Performance Monitoring                          : Enable                  
Bandwidth                                       : 50.0Gb/s                
Alarm Information:
LOS = 1 LOF = 0 LOM = 0
OOF = 0 OOM = 0 AIS = 0
IAE = 0 BIAE = 0        SF_BER = 0
SD_BER = 0      BDI = 0 TIM = 0   
FECMISMATCH = 0 FEC-UNC = 0       
Detected Alarms                                 : None
Bit Error Rate Information
PREFEC  BER                                     : 0.00E+00 
POSTFEC BER                                     : 0.00E+00 
Q-Factor                                        : 0.00 dB  
Q-Margin                                        : -5.00dB
Instantaneous Q_margin                        :  0 dB
TTI :
Remote IP addr                                  : 0.0.0.0
FEC mode                                        : Soft-Decision 15

AINS Soak                                       : None
AINS Timer                                      : 0h, 0m
AINS remaining time                             : 0 seconds