Customers could experience issues setting up 400G links using QSFP56-DD-400G-ZR transceivers plugged into PTX10001-36MR routers.

• The receiver power remains at -40.00 dBm on both sides of all links.
• Laser Output Power:
  • Site 01: 0.115 mW / -9.37 dBm
  • Site 02: 0.128 mW / -8.91 dBm
• Laser Receiver Power:
  • Both Site 01 and Site 02: 0 mW / -40.00 dBm
• Optical signal meter readings:
  • Transmitting power: -9 dBm
  • Signal from other DC: -21 dBm
• Measurements are consistent across all four links at 1550nm wavelength.

PTX10001-Site01> show interfaces diagnostics optics et-0/0/0 | match "Laser output power |Laser receiver power "

Laser output power : 0.115 mW / -9.37 dBm

Laser receiver power : 0 mW / -40.00 dBm

PTX10001-Site02> show interfaces diagnostics optics et-0/0/0 | match "Laser output power |Laser receiver power "

Laser output power : 0.128 mW / -8.91 dBm

Laser receiver power : 0 mW / -40.00 dBm

1. Verify Fiber Connections: Ensure all fiber connections are clean and properly seated. Use an optical time-domain reflectometer (OTDR) to check for any faults or breaks in the fiber.
2. Check Patch Cords: Replace existing patch cords with higher quality, low-loss patch cords to reduce signal loss.
3. Inspect Transceivers: Confirm that the QSFP56-DD-400G-ZR transceivers are functioning correctly. Swap transceivers between ports to rule out faulty modules.
4. Adjust Power Levels: If possible, adjust the transmit power levels on the transceivers to compensate for the signal loss. Ensure that the power levels are within the acceptable range for the transceivers.
5. Use Optical Amplifiers: If the link distance is close to the maximum supported by the transceivers, consider using optical amplifiers to boost the signal strength.
6. Consult JTAC: Our ZR optical supplier confirmed that the current behavior is expected. When RxLOS is asserted, the Rx power monitors are set to -40dBm within the module FW.
7. Review Link Budget: Calculate the total link budget and ensure it is within the specifications for the QSFP56-DD-400G-ZR transceivers. The observed loss of around 11.6 dB might be too high for the link to function correctly.
8. Circuit Provider Assistance: Check if your circuit provider can help reduce the link loss. They might offer better patch cords or other solutions to improve the signal quality.

Alternative Transceivers:

• JCO400-QDD-ZR-M-HP: This transceiver has a 0dBm launch power, providing more power and link budget to span the site.
• JCO400-QDD-ZR-M: Using the 400G OFEC mode can gain an extra 2dBm of margin on the Rx sensitivity, potentially closing the link. Alternatively, the 300G 8QAM mode can be used to close the link at a lower bandwidth
• QDD-400G-ZR: This module has the same -20dBm Rx power limit but often has a higher output power (around -7dBm), which might be enough to span the link/loss. However, this is not guaranteed as the output power is still specified at -10dBm minimum

By following these steps, you should be able to identify and resolve the issue with the 400G links on your QSFP56-DD-400G-ZR transceivers.