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Introduction
As data center networks race toward higher bandwidth and lower latency, 400G Ethernet has become the mainstream choice for leaf–spine fabrics and interconnects. Among the different optical standards that enable 400G, the OSFP 400G DR4 stands out for its parallel single-mode architecture, moderate reach, and high density.
Yet confusion abounds. Many engineers new to 400G assume DR4 is multimode or believe OSFP modules can be directly swapped with QSFP-DD. Both are misconceptions that can derail a project.
This article sets the record straight and provides a clear, technically accurate, and practical guide to what OSFP 400G DR4 is, how it differs from FR4/LR4/SR8, how to choose and deploy it, and what to watch for in installation and troubleshooting.
Quick Checking out OSFP 400G DR4 Optical Modules
What is OSFP 400G DR4?
- OSFP (Octal Small Form-Factor Pluggable) is a newer module form factor designed for 400G and beyond. It is slightly larger than QSFP-DD, allowing for higher power budgets and better thermal management.
- 400GBASE-DR4 is an IEEE 802.3bs Ethernet standard that uses: 1310 nm wavelength, parallel single-mode fiber (SMF), MPO-12/APC connector (12 fibers, 8 active for 4 TX + 4 RX, 4 unused), 4 parallel lanes, each 100G PAM4, reach up to 500 m.
Together, OSFP 400G DR4 means a 400G transceiver in OSFP form factor that implements the 400GBASE-DR4 standard.
The Four Common 400G Standards
A common source of mistakes is mixing DR4 with other 400G optics. The table below clears the fog.
Comparison of 400G Optical Standards
| Standard | Medium & Wavelength | Connector & Fibers | Lane structure | Reach | Typical Use Case |
| DR4 | 1310 nm SMF | MPO-12/APC, 8 fibers active | 4 × 100G PAM4 (parallel) | 500 m | Leaf–spine in data halls, cross-row |
| FR4 | 4 λ CWDM @1310 nm SMF | LC duplex | 4 × 100G (wavelength mux) | 2 km | Metro/DC interconnect within campus |
| LR4 | 4 λ CWDM @1310 nm SMF | LC duplex | 4 × 100G | 10 km | Enterprise WAN, metro links |
| SR8 | 850 nm MMF (OM4/OM5) | MPO-16 | 8 × 50G PAM4 (parallel) | 100 m | Short-reach rack-to-rack |
Key takeaways:
- DR4 = single-mode parallel 500 m.
- SR8 = multimode parallel 100 m.
- FR4/LR4 = single-mode wave-division, longer reach.
Why DR4 Uses 1310 nm PAM4 and FEC
PAM4 signaling
- Pulse Amplitude Modulation with 4 levels (PAM4) doubles data capacity per symbol compared to NRZ.
- Each DR4 lane carries 100G PAM4 at ~53.125 GBd.
- Four lanes in parallel achieve 400G.
FEC (Forward Error Correction)
- 400GBASE-DR4 requires RS-FEC (KP4) to meet BER specifications.
- Both ends must use FEC consistently - a frequent cause of “no link” if misconfigured.
Practical note: Many switches enable FEC by default on 400G ports. Always confirm.
OSFP vs QSFP-DD: Not Plug-Compatible
Both OSFP and QSFP-DD can support 400G optics, but they differ.
| Attribute | OSFP | QSFP-DD |
| Dimensions | Larger, better thermal handling | Smaller, higher faceplate density |
| Power envelope | Higher (up to ~15 W/module) | Lower (~12 W typical) |
| Physical intermate | Not compatible | Not compatible |
| Ecosystem | Rapidly growing (400G/800G OSFP modules) | Mature, widely deployed (400G/800G) |
Important: An OSFP module cannot be plugged into a QSFP-DD cage. Compatibility means they can interoperate electrically/optically over the link (if both sides are DR4), not that the modules fit the same slot.
DR4 and Breakout Use Cases
One powerful feature of DR4 is the ability to break out a 400G port into 4 × 100G DR ports.
- A 400G OSFP DR4 on a switch can connect via MPO-12 to 4 × 100GBASE-DR (LC duplex) using a breakout harness.
- Useful when you want flexible port speed mix: e.g., one 400G uplink split to multiple 100G servers.
Choosing DR4 vs Others
Step 1: Distance and cabling
- ≤100 m, multimode pre-installed → SR8 (MPO-16).
- ≤500 m, new single-mode MPO trunks → DR4 (MPO-12).
- 500 m–2 km, existing LC duplex SMF → FR4.
- Up to 10 km → LR4.
Step 2: Port form factor
- Confirm if your switch has OSFP cages or QSFP-DD cages. Order the correct form factor.
Step 3: Operational considerations
- Power and cooling budget: OSFP DR4 runs ~10–14 W.
- Density: QSFP-DD can fit more per RU, but OSFP handles power-hungry optics better.
- Breakout needs: DR4 is ideal for 400G → 4×100G DR.
Installation and Maintenance Best Practices
Installing OSFP DR4 modules
- Hot-swappable: no need to power down the switch.
- Protect against ESD during handling.
- Clean MPO-12/APC connectors with an MPO cleaning tool.
- Insert firmly until latch clicks.
- Monitor DOM/telemetry (Tx/Rx power, temperature, FEC counters).
Fiber patching guidelines
- Use the correct MPO-12 APC trunk with matching polarity (A/B/C).
- Verify patch panel polarity scheme matches both ends.
- Avoid bending fibers beyond manufacturer’s minimum radius.
- Label breakouts (400G → 4×100G) clearly.
Maintenance
- Periodic endface inspection and cleaning.
- Monitor FEC error rates: rising counters may indicate dirt or stress.
- Replace any damaged trunks immediately—parallel optics are sensitive to alignment.
Troubleshooting Guide
Common OSFP DR4 Issues and Fixes
| Symptom | Likely cause | Fix |
| Link does not come up | FEC disabled or mismatched | Enable RS-FEC consistently |
| MPO polarity mismatch | Verify A/B polarity scheme | |
| Endface dirty | Inspect & clean connectors | |
| Link flaps | Loose MPO latch | Reseat, check strain relief |
| High BER / FEC corrections | Contamination or bend stress | Clean fiber, reduce bend |
| One lane down | MPO ferrule defect or fiber break | Swap trunk, check lane mapping |
OEM vs Compatible 400G DR4 Modules
OEM
- Guaranteed standards compliance (IEEE, OSFP MSA).
- Vendor firmware support, warranty, TAC coverage.
- Higher upfront cost.
Compatible
- Typically 30–50% cheaper.
- Reputable third-party vendors code modules to be switch-compatible.
- Risk of reduced warranty or firmware lockouts.
- Must test for interoperability and monitor long-term reliability.
Tip: Run pilots and validate before large-scale rollout.
Future Outlook: Toward 800G and Beyond
- 800G OSFP modules already exist (2×FR4, DR8, SR8, etc.), doubling capacity.
- Co-packaged optics (CPO) may eventually bypass front-panel pluggables.
- OSFP form factor is favored for 800G deployments thanks to its higher thermal budget.
- Data centers planning 400G DR4 now should keep 800G OSFP migration paths in mind.
Frequently Asked Questions (FAQ)
Q1: What is OSFP 400G DR4?
A: An OSFP form-factor transceiver implementing 400GBASE-DR4: 1310 nm, 4 × 100G PAM4 parallel lanes, MPO-12/APC connector, 500 m over single-mode fiber.
Q2: What fiber type does DR4 use?
A: Single-mode (SMF). It does not use multimode; that’s SR8.
Q3: How far does 400G DR4 reach?
A: Up to 500 m on SMF.
Q4: Can OSFP DR4 plug into a QSFP-DD port?
A: No. OSFP and QSFP-DD have different cages. They can interoperate optically if both sides run DR4, but the modules themselves are not physically interchangeable.
Q5: Does DR4 require FEC?
A: Yes. 400GBASE-DR4 requires RS-FEC (KP4). Both ends must enable it.
Q6: Can DR4 be broken out to 4 × 100G?
A: Yes. Using an MPO breakout cable, one 400G DR4 can connect to four 100G DR ports.
Q7: What is the power consumption of OSFP DR4?
A: Typically 10–14 W, depending on vendor.
Conclusion
The OSFP 400G DR4 optical transceiver is a workhorse for modern data centers—providing cost-effective 500 m reach over SMF with parallel optics. Correctly deployed, it enables both dense 400G fabrics and flexible breakouts to 100G.
When selecting, focus on form factor (OSFP vs QSFP-DD), distance (500 m SMF), cabling (MPO-12/APC with polarity), and FEC requirements. For operators preparing for AI workloads, spine–leaf fabrics, or multi-rack connectivity, DR4 provides a balanced option between short-reach SR8 and long-reach FR4/LR4.
If you need validated OSFP 400G DR4 optics, breakout cables, or compatibility guidance, the team at Network-Switch.com can help. As an authorized distributor of Cisco, Huawei, and Ruijie, plus our own line of fiber cables and optical modules, we offer both products and expertise to build reliable high-speed networks.
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