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Spirent TestCenter: What is the auto tune feature and how to configure it?

  • PX3-400G-T2 module, PX3-QSFP-DD-X module or appliances
    • 400G, 200G, 100G, 50G 
  • 5.18 (or higher)
  • STC-L1 mode (aka L1 Services)
  • Auto tune (emphasis settings)
  • New or "unknown" (by STC) optical transceivers, DAC, AOC with no or marginal link

Auto tune is a new feature introduced in 5.18 release (Jan 2021) for L1 Services, and it is via the command sequencer, this is intended to address most of the problems seen on the field related to new cables and/or optical transceivers that get plugged into our equipment and we have no link.

Usually, without this tool, the process of finding optimal emphasis values is painful and often requires engineering support, so this feature will overcome this issue by finding the correct emphasis values automatically.

  • This script helps find the optimal emphasis values for the "source" port (i.e., emphasis values help shape the electrical signal on the transmit or "source" port).
  • The settings found, can be used on transceivers/interconnects of the same kind.
  • If different transceivers/interconnects are used, please run the Auto Tune command using the different transceivers as "source" ports.

  1. Make sure TestCenterIQ is enabled under TestCenter IQ Settings
  2. Connect the STC port to each other using the transceivers/interconnects needing to be tuned.
    1. The script runs on pairs of ports. A "source" and a "destination" port.
    2. In each iteration, changes to the "source" port's settings (e.g., pre and post emphasis, and main tap swing) is made.
    3. The effect of the changes is then measured by checking the pre-FEC BER (i.e., "raw," uncorrected bit error rate) on the "destination" port.
    4. After multiple iterations, the settings that correspond to the lowest pre-FEC BER is reported.
  3. Set the ports you want to run the Auto Tune feature on to STC-L1 Mode Performance Mode and hit "Apply"

  1. Open Command Sequencer, either under "Sequencer" button at the top tool bar (almost all the way to the right), or under "Command Sequencer" Tab at the top right of STC GUI
  2. Click on "Edit Sequence.." and find "L1 Transceiver Auto Tune Command" under L1Test section, then just add it
    • enlightenedEach command will tune a pair of ports that are directly connected to each other. You can add as many such commands needed depending on how many pairs of ports you want to tune.

  1. Right click on the command, select "Edit sequence" and select the pair of ports you want to tune, and click OK
  1. Then start the sequence
    • enlightenedEach command would take ~10 minutes to complete
  1. Once the sequencer finishes, you will see a log messages indicating the Emphasis values configured and you will see the ports UP

Questions related auto-tune:

  1. After running the auto-tune, are the settings stored somewhere in memory or so, to remember that particular optic has been already auto-tuned?
    • if auto-tune command is completed successfully, the tuned values are already configured to the chip, and the display in the GUI will also be auto-refreshed.  If a user wants to save it for re-use, they need to do one more step: click the “save as New Emphasis File” button under the “Transceiver Setting.”
  2. Where are these settings stored?
    • The settings will be stored in a file located in chassis:  /mnt/spirent/testmodule/slot$ /ccpu(CCPU_ID)/l1_trained_emphasis.  Please note that after the chassis upgrade, the saved file will be gone
  3. And, what is stored, the number/part number of the module?
    • The number/part number of the module and the associated emphasis values will be stored.


Product : Spirent TestCenter