We are planning to connect a QSFP28 NIC to an SN4600 switch with QSFP56 ports, but I have come across conflicting information online.
Do these two different technologies work together? If they do, is it appropriate to use a QSFP56 transceiver on the QSFP28 NIC, or should we use a setup where the NIC side remains QSFP28 and the switch side uses QSFP56?
Hi @ugurbas
QSFP28 and QSFP56 technologies are related but have significant differences in their electrical interfaces and data rates. Here is a detailed explanation of their compatibility:
1. Form Factor: Both QSFP28 and QSFP56 share the same physical form factor, allowing them to fit into the same ports physically.
2. Backward Compatibility: QSFP56 transceivers are backward compatible with QSFP28 ports. This means you can use a QSFP56 transceiver in a QSFP28 port, but it will operate at the lower data rate of the QSFP28 standard (100 Gbps instead of 200 Gbps).
3. Electrical Interface Differences:
• QSFP28 uses 4 lanes of 25 Gbps each (totaling 100 Gbps) with NRZ modulation.
• QSFP56 uses 4 lanes of 50 Gbps each (totaling 200 Gbps) with PAM4 modulation. These differences mean that while the form factor is compatible, the electrical signaling and data rates must align for proper operation.
Regards,
Vladislav
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