Every transceiver part number follows the same structure:
[Speed] [Form Factor] [Reach Type + Lane Count]
| Full Name | Speed | Form Factor | Reach + Lanes |
|---|---|---|---|
| 100G QSFP28 LR4 | 100G | QSFP28 | LR, 4 lanes |
| 400G QSFP-DD DR4 | 400G | QSFP-DD | DR, 4 lanes |
| 400G OSFP FR4 | 400G | OSFP | FR, 4 lanes |
| 800G QSFP-DD DR8 | 800G | QSFP-DD | DR, 8 lanes |
The form factor defines the physical housing, connector type, and which port it fits. The reach suffix defines the optical technology, fiber type, and maximum distance. These are independent axes. A QSFP-DD port can hold a DR4, an FR4, or an LR4 — the form factor stays constant while the optics change.
| Attribute | QSFP28 | QSFP-DD | OSFP |
|---|---|---|---|
| Typical speed tier | 100G | 400G / 800G | 400G / 800G |
| Lane count | 4 x 25G | 8 x 50G (or 8 x 100G for 800G) | 8 x 50G (or 8 x 100G for 800G) |
| Max electrical lanes | 4 | 8 (dual-row) | 8 |
| Connector rows | Single | Double (backward-compatible row) | Single (wider housing) |
| Port density (1U 32-port switch) | High | High | Lower (~24 ports typical) |
| Max power per module | ~3.5W | ~12W | ~15W+ |
| Thermal envelope | Low | Medium-high | High (designed for active cooling) |
| Backward compatibility | None | QSFP-DD ports accept QSFP28 modules (electrically) | None |
| Ecosystem maturity | Very mature | Mature, dominant 400G standard | Growing, preferred for 800G hyperscale |
| Typical use case | 100G leaf-spine, enterprise core | 400G spine, AI cluster, DCI | 800G AI cluster spine, hyperscale |
On backward compatibility: A QSFP-DD port accepts a QSFP28 module because the double-row connector's lower row is electrically compatible with QSFP28. The reverse does not work. OSFP uses a physically wider housing and shares no backward compatibility with either.
The suffix after the lane count — SR4, DR4, FR4, LR4, ER4, ZR — defines the optical technology, not the form factor. Here is the full breakdown:
| Suffix | Full Name | Typical Distance | Fiber Type | Connector | Primary Use Case |
|---|---|---|---|---|---|
| SR | Short Reach | Up to 100m (SR4) | OM3/OM4 multimode | MPO-12 | Intra-rack, top-of-rack to aggregation |
| DR | Direct Reach | Up to 500m | OS2 single-mode | MPO-12 | Within a campus or data center building |
| FR | Far Reach | Up to 2km | OS2 single-mode | LC duplex (FR4 uses MPO) | Inter-building, short DCI |
| LR | Long Reach | Up to 10km | OS2 single-mode | LC duplex | Metro DCI, campus-to-campus |
| ER | Extended Reach | Up to 40km | OS2 single-mode | LC duplex | Regional metro links |
| ZR | Zero-dispersion Reach | Up to 80km (ZR) / 1000km+ (ZR+) | OS2 single-mode | LC duplex | Long-haul, coherent DCI |
These three dominate 400G QSFP-DD procurement and they are not interchangeable.
DR4 runs 4 x 100G lanes over parallel single-mode fiber with an MPO-12 connector, up to 500m. It is the lowest-cost 400G single-mode option and the right call for intra-campus or within-building runs where MPO infrastructure is already in place.
FR4 uses 4-wavelength CWDM4 multiplexing over a single LC duplex fiber pair, up to 2km. It costs more than DR4 but eliminates the MPO-to-LC breakout problem and suits inter-building links cleanly.
LR4 uses 4-wavelength LAN-WDM multiplexing over LC duplex single-mode, up to 10km. This is the standard for metro DCI and any link that crosses more than a city block. Expect a meaningful price premium over DR4 at the same speed tier.
If your fiber plant uses MPO trunks and runs stay under 500m, DR4 is the right choice. Duplex LC between buildings at 2km or less, use FR4. Beyond 2km, move to LR4 or ER4 depending on distance.
| Target Speed | Recommended Form Factor | Notes |
|---|---|---|
| 100G | QSFP28 | Mature ecosystem, lowest cost per port |
| 400G | QSFP-DD | Dominant standard; OSFP also viable for high-power optics |
| 400G (high-density, hyperscale) | OSFP | Better thermal management for coherent ZR/ZR+ |
| 800G | QSFP-DD or OSFP | OSFP preferred for active-cooling chassis; QSFP-DD DR8 widely stocked |
| Deployment Scenario | Fiber Available | Recommended Reach Type |
|---|---|---|
| Intra-rack or top-of-rack | OM3/OM4 multimode | SR4 |
| Within data center building, under 500m | OS2 single-mode, MPO | DR4 |
| Inter-building, 500m to 2km | OS2 single-mode, LC duplex | FR4 |
| Campus-to-campus or metro DCI, 2km to 10km | OS2 single-mode, LC duplex | LR4 |
| Regional metro, 10km to 40km | OS2 single-mode | ER4 |
| Long-haul DCI, 40km to 80km+ | OS2 single-mode | ZR / ZR+ |
These two steps give you the exact part name with no ambiguity. 400G, within-building, MPO plant: 400G QSFP-DD DR4. 100G, metro DCI at 8km, LC duplex: 100G QSFP28 LR4.
Cisco, Arista, Juniper, and Huawei all validate transceiver firmware before allowing a port to come up. A module that is not coded for your specific platform will throw an unsupported-transceiver warning and may disable the port entirely — even when the optical specs are identical to the OEM module.
This is a firmware check, not a hardware incompatibility. Third-party modules coded for your switch platform pass that check and come up clean, no warning messages, the same as an OEM module would.
When evaluating a supplier, confirm they provide platform-specific coding for each module — not a generic firmware load. The coding must match the switch OS version you are running. Arista EOS, Cisco NX-OS, Juniper Junos, and Huawei VRP each run their own validation logic, and a mismatch on any one of them will cause problems.
HYTOPTODEVICE stocks QSFP28, QSFP-DD, and OSFP modules across the full reach spectrum — from 100G QSFP28 SR4 for intra-rack OM4 runs through to 800G QSFP-DD DR8 for AI cluster spine builds. CWDM and DWDM variants are available at 10KM, 40KM, 80KM, and up to 120KM for long-haul and metro DCI deployments.
Every module ships with platform-specific coding for Cisco, Arista, Juniper, and Huawei — drop-in compatible, no unsupported-transceiver warnings. OEM/ODM and white-label options are available for resellers and VARs who need custom firmware or branded packaging. Factory-direct pricing runs 60 to 90 percent below OEM list price at any volume, single-unit or bulk.
Q1:What does DR4 mean on a transceiver?
A:DR4 stands for Direct Reach, 4 lanes. It uses 4 x 100G parallel single-mode lanes over an MPO-12 connector and supports distances up to 500m on OS2 fiber. It is the most cost-effective 400G single-mode option for within-building runs.
Q2:Can I plug a QSFP-DD module into a QSFP28 port?
A:No. A QSFP-DD module is physically larger and uses a double-row connector that will not fit a QSFP28 port. The reverse works in some cases: a QSFP28 module can be inserted into a QSFP-DD port because the lower connector row is electrically backward-compatible, though you will only get 100G throughput on that port.
Q3:Is OSFP backward compatible with QSFP-DD?
A:No. OSFP uses a wider housing and a different connector geometry. It is not mechanically or electrically compatible with QSFP-DD ports. OSFP ports only accept OSFP modules.
Q4:What is the difference between FR4 and LR4 at 100G or 400G?
A:Both use 4-wavelength WDM multiplexing over LC duplex single-mode fiber. FR4 uses CWDM4 wavelengths and reaches up to 2km. LR4 uses LAN-WDM wavelengths and reaches up to 10km. LR4 modules carry a higher price. If your link is under 2km, FR4 is the better value.
Q5:Why does my switch throw an unsupported-transceiver warning for a third-party module?
A:The switch is running a firmware validation check, not detecting a hardware fault. The module needs to be coded with the correct platform identifier for your specific switch OS. A properly coded third-party module passes this check and operates identically to an OEM module.
Q6:When should I choose OSFP over QSFP-DD for 400G or 800G?
A:OSFP is the better choice when your chassis supports active cooling per port and you are running coherent ZR or ZR+ optics that dissipate more than 12W per module. For standard 400G DR4 or FR4 deployments, QSFP-DD offers higher port density and a more mature ecosystem at lower cost.
Once you separate the form factor from the reach type, the naming convention is straightforward. QSFP28 for 100G. QSFP-DD for 400G and 800G in high-density builds. OSFP for 800G hyperscale and coherent applications. Then layer in SR, DR, FR, LR, ER, or ZR based on your fiber plant and link distance. Get both axes right and you will not order the wrong module again.
For factory-direct stock across all three form factors with platform-specific coding for Cisco, Arista, Juniper, and Huawei, visit hytoptodevice.com.
