https://network-switch.com/pages/about-us
Introduction: Why 400G and 800G Matter?
The rise of AI training, HPC (high-performance computing), and hyperscale cloud services has pushed network bandwidth demands higher than ever. Ten years ago, 40G and 100G were cutting-edge. Today, many data centers are already migrating to 400G, and some are planning or testing 800G.
Optical modules are at the heart of this transition. They convert electrical signals into light and back, enabling servers and switches to communicate over fiber. Choosing between 400G and 800G optical modules depends on your workloads, scale, and budget. This guide breaks down the differences, use cases, and deployment advice in simple but detailed terms.
Optical Modules Overview
What are Optical Modules?
An optical module (or optical transceiver) is a pluggable device inserted into switches, routers, or NICs.
Functions:
- Convert electrical signals ↔ optical signals.
- Provide a standardized interface (SFP, QSFP, OSFP, CFP2, etc.).
- Support different reaches: short-reach (within rack/row), medium-reach (between rows), long-haul (DCI, telecom).
400G and 800G modules are typically in form factors like QSFP-DD and OSFP, which can fit many high-speed lanes into one module.
400G Optical Modules
400G is already widely deployed in modern cloud and enterprise data centers.
Common standards:
- 400GBASE-SR8: multimode fiber (OM4/OM5), up to 100m.
- 400GBASE-DR4: single-mode, 500m reach, often used with breakout (4×100G).
- 400GBASE-FR4: single-mode, 2km, using 4 wavelengths.
- 400GBASE-LR4: single-mode, 10km, for longer links.
Packaging:
- QSFP-DD (Quad Small Form Factor Pluggable – Double Density).
- OSFP (Octal Small Form Factor Pluggable).
Applications:
- Leaf–spine links in data centers.
- AI pods with hundreds of GPUs.
- Enterprise networks needing higher capacity.
Power consumption: ~10–14W per module.
800G Optical Modules
800G is newer, aimed at hyperscale cloud and AI/HPC clusters.
Common standards:
- 800G DR8: single-mode, 500m reach, 8 parallel 100G lanes.
- 800G FR8: single-mode, 2km+, 8 wavelengths at 100G each.
- 800G 2×FR4: dual FR4 in one module, each 400G.
- 800G SR8: multimode, 100m.
Packaging:
- QSFP-DD800 (evolved QSFP-DD standard).
- OSFP (popular for 800G, slightly larger than QSFP-DD).
- COBO (embedded, experimental).
Applications:
- Hyperscale AI training clusters (thousands of GPUs).
- Long-distance DCI (data center interconnect).
- Early preparation for 1.6T upgrades.
Power consumption: 16–20W+, requiring stronger airflow or liquid cooling.
400G vs 800G: Side-by-Side Comparison
| Aspect | 400G | 800G |
| Lane Speed | 8×50G PAM4 or 4×100G PAM4 | 8×100G PAM4 |
| Reach Options | SR8 (100m MM), DR4 (500m SM), FR4/LR4 (2–10km) | DR8 (500m SM), FR8 (2km+), SR8 (100m MM) |
| Packaging | QSFP-DD, OSFP | QSFP-DD800, OSFP, COBO |
| Power | ~10–14W | ~16–20W+ |
| Density | 36–40 ports per 1RU (QSFP-DD) | ~32 ports per 1RU (OSFP, higher cooling) |
| Maturity | Widely deployed, production volume | Early stage, limited suppliers |
| Use Cases | DC leaf–spine, AI pods, mid-scale HPC | Hyperscale AI, large DCI, 1.6T prep |
👉 Summary: 400G is mainstream and cost-effective; 800G is cutting-edge, higher power, higher density, designed for hyperscale needs.
Deployment Considerations
Switch compatibility
- 400G: QSFP-DD and OSFP are both common.
- 800G: OSFP is gaining traction, QSFP-DD800 is an alternative.
Cabling
- 400G DR4: MPO/MTP-12 connectors.
- 400G FR4/LR4: duplex LC, CS, or MDC.
- 800G DR8/FR8: MPO/MTP-16 or duplex MDC/CS.
Power and cooling
- 400G modules need ~10–14W per port.
- 800G modules can draw 20W+, requiring optimized airflow or liquid cooling.
Cost
- 400G optics are dropping in price as adoption grows.
- 800G optics remain premium, early adopter stage.
Migration planning
- Many operators deploy 400G now and design rack layouts to support future 800G upgrades.
- For those planning 1.6T in a few years, 800G may be a better “future-proof” choice.
Use Cases in AI and Data Centers
400G
- Data center leaf–spine fabrics (≤500m).
- AI training pods up to ~512 GPUs.
- Enterprise/hybrid cloud where cost is key.
800G
- Hyperscale AI clusters with 2000+ GPUs.
- Large-scale HPC systems.
- Long-distance DCI at multi-terabit scale.
- Cloud operators preparing for 1.6T.
Typical Scenario Guidance
| Scenario | Recommended Module |
| Standard DC leaf–spine (<500m) | 400G DR4 / FR4 |
| AI training pod (≤512 GPUs) | 400G DR4 + MPO/MTP |
| Hyperscale AI cluster (>2000 GPUs) | 800G DR8 / FR8 |
| Long-distance DCI (10km+) | 400G LR4 / 800G FR8/DCO |
Future Outlook
- 400G: Will remain the mainstream for most data centers and AI pods over the next 3–5 years.
- 800G: Rapid adoption in hyperscale environments; volume production will drive costs down.
- 1.6T: Standards in development, likely using co-packaged optics (CPO). MDC/CS connectors may become the duplex standard, while MPO/MTP handles parallel optics.
FAQs
Q1: Can 400G and 800G modules interoperate?
A: Not directly. They need matching speeds at both ends. Some switches support both but require separate modules.
Q2: Which form factor is better, QSFP-DD or OSFP?
A: OSFP supports more thermal headroom and future 1.6T, while QSFP-DD has backward compatibility with 100G/200G.
Q3: Why does 800G consume more power?
A: Because it doubles lane speeds (100G per lane), requiring more DSP power, PAM4 signal processing, and stronger cooling.
Q4: How do MDC/CS connectors fit in?
A: They replace LC in 400G/800G duplex optics, offering 2× density.
Q5: Is 400G enough for AI clusters?
A: Yes for mid-size clusters. Large hyperscale clusters increasingly need 800G for GPU-to-GPU traffic.
Q6: Should DCI deployments skip 400G and go straight to 800G?
A: It depends. Many deploy 400G LR4/FR4 today. If planning 10+ years ahead, 800G may be more efficient.
Q7: Do I need OM5 multimode for 400G/800G?
A: Not always. OM4 often suffices for SR4/SR8. Single-mode OS2 is required for DR/FR/LR.
Q8: How do I ensure compatibility across vendors?
A: Always buy end-to-end validated solutions (switch + NIC + optics + cables). Vendors like network-switch.com provide tested sets.
Conclusion
400G and 800G optical modules are both essential for modern networking:
- 400G: Today’s mainstream, cost-effective, widely supported.
- 800G: The future of hyperscale AI, HPC, and DCI, with higher power and cost but unmatched density.
How to choose:
- If you run standard data centers or medium AI pods → 400G is ideal.
- If you operate hyperscale clusters or plan for 1.6T → 800G is the strategic choice.
Did this article help you or not? Tell us on Facebook and LinkedIn . We’d love to hear from you!
