SFP, SFP+, SFP28, QSFP28, QSFP-DD and OSFP explained — lane rates, typical speeds and how to read a port.
Updated October 2026 · AltoChip team · General reference — project specifics are confirmed in each quotation.
The cage on your switch or NIC decides the form factor. A module must physically fit the cage and run at a rate the port supports. Port speed and cage type are on the device datasheet or front-panel label — that is the first line of every optical RFQ.
| Form factor | Electrical lanes × rate | Typical speed | Common use |
|---|---|---|---|
| SFP | 1 × 1G | 1G | Management, legacy access |
| SFP+ | 1 × 10G | 10G | Server NICs, access switches |
| SFP28 | 1 × 25G | 25G | Server-to-leaf |
| QSFP+ | 4 × 10G | 40G | Legacy aggregation |
| QSFP28 | 4 × 25G (or 2 × 50G PAM4) | 100G | Leaf-spine, server uplinks |
| QSFP56 | 4 × 50G PAM4 | 200G | HPC / AI NICs |
| QSFP-DD | 8 × 50G or 8 × 100G PAM4 | 400G / 800G | Spine, AI fabrics |
| OSFP | 8 × 50G or 8 × 100G PAM4 | 400G / 800G | AI fabrics, high-power optics |
Typical values for orientation; the device datasheet is authoritative.
Some cages accept smaller modules (for example SFP+ in an SFP28 port, or QSFP28 in a QSFP-DD port), but the port must be configured for the lower speed and the platform must support it. QSFP-DD and OSFP are not interchangeable with each other. Confirm with the device documentation before mixing generations.