QSFP56 ports accept QSFP28 devices

Hi Mellanox,

according to note 5 in this table:


I assume it is possible to connect the MCX653106A-ECAT-SP ConnectX-6 VPI Adapter Card featuring QSFP56 connector to a Xilinx FPGA with 4x SFP28 connectors, using a QSFP28 to SFP28 breakout cable.

The FPGA can reach 4x25Gb/s using the four SFP28. What is the maximum bandwidth in the connectx 6 in this setup (100 or 50Gb/s) ?

best regards

my concern is related to modulation protocol in use:

  • QSFP56 is using PAM4
  • QSFP28 is using NRZ

does a QSFP56 port switches to NRZ modulation when a QSFP28 cable is plugged ?

Hello Raphael,

Thank you for posting your inquiry on the NVIDIA Networking Community.

The ConnectX-6 VPI adapter supported PAM4 and NRZ. See the following link for all Features available for the ConnectX-6 adapter → https://docs.mellanox.com/display/ConnectX6Firmwarev20292002/Changes+and+New+Feature+History

To connect the cable to the ConnectX-6, you need to use the MAM1Q00A-QSA28 module as mentioned in the f/w RN (Search for MAM1Q00A-QSA28) → https://docs.mellanox.com/display/ConnectX6Firmwarev20292002/Firmware+Compatible+Products

Thank you and regards,

~NVIDIA Networking Technical Support