FEC statistics histogram

To monitor the performance of the Forward Error Correction (FEC) algorithm on the router-receive side of the host interface, SR Linux can display a histogram representation of the number of symbol errors per RS-528 or RS-544 codeword. The FEC codewords are categorized into 16 bins (bin0 through bin15) based on the number of symbol errors detected within each codeword. SR Linux displays how many codewords fall into each symbol-error bin. The per-bin RS-FEC statistics can help monitor link quality and identify when FEC correction is nearing its limit.

While correctable errors can be anticipated, particularly at higher speeds, the FEC histogram can help determine if the FEC algorithm is approaching or exceeding the ability to correct errors on the link. In a well-performing link, corrections are expected to cluster in the lower portion of the range, with higher correction counts becoming exponentially less common.

Hardware support for FEC histograms

The following table lists SR Linux per-platform support for FEC histograms. The platform support can be one of the following:

  • Full – The FEC histogram is available on all PHY ports of the platform.

  • Partial – The FEC histogram is available on a subset of the PHY ports of the platform.

  • Not supported – The FEC histogram is not available on any of the PHY ports of the platform.

Table 1. Hardware support for FEC histograms
Platform Support Notes
7220 IXR-H5 Full
7220 IXR-H5-32D Full
7220 IXR-H5-64D Full
7220 IXR-H5-64O-320 Full
7220 IXR-H6 Full
7220 IXR-H6-64O Full
7220 IXR-H4I Full
7220 IXR-H4-32D Full
7220 IXR-H2 Full Histogram yes; no pre-FEC BER
7220 IXR-D4 Partial

Supported: ethernet-1/1 through ethernet-1/8 (PHY ports 1–8).

Not supported: PHY ports 9–36.
7220 IXR-H3 Not supported
7220 IXR-D1 Not supported
7220 IXR-D2 Not supported
7220 IXR-D2L Not supported
7220 IXR-D3 Not supported
7220 IXR-D3L Not supported
7220 IXR-D5 Not supported
7220 IXR-D5T Not supported
7250 IXR-10e Gen 3 Full
7250 IXR-18e Full
7250 IXR-6e-Gen 3 Full
7250 IXR-X4 Full
7250 IXR-6e/10e (mixed system) Full
7250 IXR Gen 2c+ IXR-10e Partial Supported: PHY ports 1–24, 25, 28, 31, 34, 37, 40, 43 to 60
7250 IXR 10e-Gen 2c+/Gen 3 Partial Same port list as 7250 IXR Gen 2c+ IXR-10e
7250 IXR IXR-6e-Gen 2c+ Partial Same port list as 7250 IXR Gen 2c+ IXR-10e
7250 IXR IXR-6e-Gen 2c+/Gen 3 Partial Same port list as 7250 IXR Gen 2c+ IXR-10e
7250 IXR-X1b Partial

Supported: QSFP28 PHY ports 1 through 24.

Not supported: QSFPDD PHY ports 25 through 36.
7250 IXR-10 Not supported FEC statistics are not available on 7250 IXR Gen 2 platforms.
7250 IXR-6 Not supported FEC statistics are not available on 7250 IXR Gen 2 platforms
7250 IXR-X3b Not supported
7215 IXS Not supported

Displaying the FEC statistics histogram

To display the FEC statistics histogram, use the info from state command in candidate or running mode, or the info command in state mode.

The following example displays a FEC statistics histogram. In the histogram, bin0 indicates the number of codewords containing 0 symbol errors, bin1 indicates the number of codewords containing 1 symbol errors, and so on, up to bin15.

Bins 1 through 15 are shown for RS-544 FEC; bins 1 through 7 are shown for RS-528 FEC.

  • For RS-528 FEC, codewords with greater than 7 symbol errors are classified as uncorrectable. Reception of such codewords also increments the frame-error-count counter.

  • For RS-544 FEC, codewords with greater than 15 symbol errors are classified as uncorrectable. Reception of such codewords also increments the frame-error-count counter.

--{ candidate shared default }--[  ]--
# info from state interface ethernet-2/5 ethernet forward-error-correction 
    operational-host-if-fec cl119-rs544
    statistics {
        host-if-fec-router {
            status locked
            frame-error-count 10        // 10 rs544 codewords were uncorrectable
            pre-fec-ber {
                instant 7.134118E-09
            }
            histogram {
               bin0       1234567891234  // number of rs544 codewords with 0 symbols errors 
               bin1       10             // number of rs544 codewords with 1 symbol error   
               bin2       20             // number of rs544 codewords with 2 symbol errors  
               bin3       30             // number of rs544 codewords with 3 symbol errors  
               bin4       40             // number of rs544 codewords with 4 symbol errors  
               bin5       50             // number of rs544 codewords with 5 symbol errors  
               bin6       0              // number of rs544 codewords with 6 symbol errors  
               bin7       0              // number of rs544 codewords with 7 symbol errors  
               bin8       60             // number of rs544 codewords with 8 symbol errors   
               bin9       0              // number of rs544 codewords with 9 symbol errors   
               bin10      0              // number of rs544 codewords with 10 symbol errors  
               bin11      0              // number of rs544 codewords with 11 symbol errors  
               bin12      0              // number of rs544 codewords with 12 symbol errors  
               bin13      0              // number of rs544 codewords with 13 symbol errors  
               bin14      0              // number of rs544 codewords with 14 symbol errors  
               bin15      0              // number of rs544 codewords with 15 symbol errors  
          
        }
    }

Clearing FEC statistics

FEC histogram statistics are reset to zero when the SR Linux device is started or reset or the counters are cleared. You can clear the counters using a tools command that clears both regular FEC statistics and FEC histogram counters on supported platforms.

The following example clears FEC statistics counters.


# tools interface ethernet-1/1 ethernet forward-error-correction statistics host-if-fec-router clear