The abbreviation QSFP28 means Quad Small Form-factor Pluggable 28. A four-lane hot-pluggable form factor commonly used for 100G Ethernet, typically with four 25G electrical lanes. Its practical scope is defined by how it is applied in 100G SR4, CWDM4, LR4, ER4, not by the abbreviation alone.
For QSFP28, interoperability and acceptance start with the governing specification. The mechanical, electrical, thermal, and management requirements normally come from the relevant MSA and host-platform specification. Project documentation should identify the edition, host assumptions, and any vendor-specific limits that apply.
A useful boundary is the difference between QSFP28 and QSFP56. The former describes a four-lane hot-pluggable form factor commonly used for 100G Ethernet, typically with four 25G electrical lanes. The latter describes a four-lane PAM4 form factor supporting 200G through four 50G electrical lanes. Keeping that distinction clear prevents an interface, performance value, or commercial condition from being assumed where it was never specified.
When selecting or documenting QSFP28, verify cage type, electrical lane mapping, power class, cooling, firmware, and backward compatibility. A common mistake is to assume that support for SFP automatically confirms support for QSFP28; the exact data sheet, host configuration, and test conditions must show that relationship.
Frequently Asked Questions
What separates QSFP28 from QSFP56?
The scope is different: QSFP28 is a four-lane hot-pluggable form factor commonly used for 100G Ethernet, typically with four 25G electrical lanes. QSFP56 is a four-lane PAM4 form factor supporting 200G through four 50G electrical lanes. The applicable specification and system requirement determine how they interact.
Where is QSFP28 normally used?
Typical use includes 100G SR4, CWDM4, LR4, ER4. The exact implementation still depends on the host equipment, link design, environment, and governing specification.
What should a QSFP28 specification include?
It should state cage type, electrical lane mapping, power class, cooling, firmware, and backward compatibility. These details allow a supplier or engineer to verify the requirement instead of relying only on the term QSFP28.
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