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100G vs 400G vs 800G: How to Plan Your Network Upgrade Path

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Network Switches
IT Hardware Experts
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Introduction: Why Upgrade Speeds Matter

Modern workloads such as AI training, cloud computing, video streaming, and HPC (high-performance computing) are pushing networks harder than ever. If the network cannot keep up, servers and GPUs sit idle waiting for data.

This is why many IT teams are planning their upgrade path: moving from 100G → 400G → 800G. Each step offers better performance but comes with new challenges around cost, power, cooling, and cabling.

In this guide, we’ll explain the key differences between 100G, 400G, and 800G, and help you decide when and how to move forward.

100G to 800G Upgrade Path

Network Upgrade Path Overview

What do 100G, 400G, and 800G mean?

  • The number (100G/400G/800G) refers to the total data rate of the port or module.
  • These speeds are delivered by lanes - multiple electrical or optical channels combined: 100G: 4×25G NRZ, or 2×50G PAM4. 400G: 8×50G PAM4 or 4×100G PAM4. 800G: 8×100G PAM4.
  • Newer speeds use PAM4 modulation (4-level pulse amplitude modulation), which doubles throughput compared to NRZ.
  • Common form factors: 100G: QSFP28. 400G: QSFP-DD, OSFP. 800G: OSFP, QSFP-DD800.

100G Optical Modules Overview

Maturity: Widely deployed and well-understood.

Common standards:

  • 100GBASE-SR4: 100m multimode fiber (MPO-12).
  • 100GBASE-LR4: 10km single-mode (LC duplex).
  • 100G CWDM4: 2km single-mode (LC duplex).

Form factor: QSFP28.

Applications:

  • Enterprise data centers.
  • Metro and backbone networks.
  • Smaller-scale AI/HPC where cost is the main driver.

Strengths:

  • Lowest cost per module.
  • Very mature ecosystem.

Limitations: Not enough bandwidth for modern AI/HPC clusters.

400G Optical Modules Overview

Maturity: Rapid adoption in hyperscale and large enterprise data centers.

Common standards:

  • 400G DR4: 500m on single-mode (MPO-12).
  • 400G FR4: 2km single-mode (LC/MDC/CS).
  • 400G LR4: 10km single-mode.
  • 400G SR8: 100m multimode (MPO-16).

Form factors: QSFP-DD, OSFP.

Applications:

  • Cloud data centers, AI pods, leaf–spine fabrics.
  • Enterprises moving from 100G to 400G to handle growth.

Strengths:

  • Cost per bit lower than 100G.
  • Ecosystem growing quickly.

Limitations:

  • Higher power consumption (10–14W).
  • Requires better cooling.

800G Optical Modules Overview

Maturity: Early stage, but quickly being adopted in hyperscale AI/HPC clusters.

Common standards:

  • 800G DR8: 500m on single-mode (MPO-16).
  • 800G FR8: 2km+ single-mode (duplex CS/MDC).
  • 800G 2×FR4: Dual 400G in one module.
  • 800G SR8: 100m multimode.

Form factors: OSFP, QSFP-DD800.

Applications:

  • Hyperscale AI clusters with thousands of GPUs.
  • Long-distance data center interconnect (DCI).
  • Preparing for 1.6T upgrades.

Strengths:

  • Supports the most demanding workloads.
  • Designed with future 1.6T in mind.

Limitations:

  • Expensive.
  • Power draw ~16–20W+, requiring advanced cooling.

Side-by-Side Comparison

100G vs 400G vs 800G

Aspect 100G 400G 800G
Lane Speed 4×25G NRZ / 2×50G PAM4 8×50G PAM4 / 4×100G PAM4 8×100G PAM4
Form Factors QSFP28 QSFP-DD / OSFP OSFP / QSFP-DD800
Power ~3–5W ~10–14W ~16–20W+
Ecosystem Very mature Rapid adoption Early adoption
Cost Lowest Falling quickly Highest currently
Best Use Enterprises, legacy DC, metro links Cloud DC, AI pods, leaf–spine DCN Hyperscale AI, HPC, large-scale DCI

Planning an Upgrade Path

planning upgrade path

Step 1: Assess Workloads

  • Enterprise apps (VMs, storage, ERP) → 100G is often enough.
  • Cloud / SaaS / streaming → 400G for east–west traffic.
  • AI/HPC clusters → 400G now, 800G if scaling to thousands of GPUs.

Step 2: Align With Growth Timeline

  • 100G: fine for current, stable workloads.
  • 400G: mainstay for the next 3–5 years.
  • 800G: forward-looking, suited for 5–10 year planning.

Step 3: Cabling & Connectors

  • 100G: LC duplex, MPO-12.
  • 400G: MPO-12/16, LC, CS, MDC.
  • 800G: MPO-16, CS, MDC (new high-density connectors).

Step 4: Plan for Power & Cooling

  • 100G: simple airflow cooling.
  • 400G: requires careful airflow design.
  • 800G: may require liquid cooling in dense deployments.

Step 5: Ensure End-to-End Consistency

  • Match NIC ↔ switch ↔ optical module ↔ cabling.
  • Mixing vendors without validation can cause costly issues.

Use Cases in Data Centers & AI

100G: Enterprises, branch DCs, cost-sensitive deployments.

400G

  • Cloud providers, AI training pods (≤512 GPUs).
  • Large enterprises modernizing leaf–spine fabrics.

800G

  • Hyperscale AI clusters (>2000 GPUs).
  • HPC with ultra-low latency needs.
  • Long-distance DCI with extreme bandwidth.

Scenario to Speed Guidance

Scenario Recommended Speed
Enterprise DC 100G
Cloud leaf–spine fabric 400G
AI training pod (≤512 GPUs) 400G
Hyperscale AI (>2000 GPUs) 800G
Long-distance DCI 400G/800G

Future Outlook

  • 100G: Will remain in enterprise and access layers for years due to cost efficiency.
  • 400G: Expected to dominate as the mainstream for the next 5 years.
  • 800G: Growing fast in hyperscale; prices will drop as adoption increases.
  • Beyond 800G: 1.6T optics are already being developed, likely with co-packaged optics (CPO) for efficiency.

FAQs

Q1: Should enterprises skip 100G and go straight to 400G?
A: If workloads are growing fast, yes. For steady workloads, 100G is still fine.

Q2: Is 400G enough for AI clusters?
A: Yes for mid-sized clusters. Hyperscale clusters increasingly need 800G.

Q3: How to deal with 800G module power consumption?
A: Plan rack design for higher airflow, or adopt liquid cooling.

Q4: Which form factor is better, QSFP-DD or OSFP?
A: QSFP-DD = backward compatibility; OSFP = thermal headroom and future 1.6T.

Q5: How do connectors like MPO/MTP and CS/MDC fit in?
A: MPO/MTP for parallel optics; CS/MDC for high-density duplex optics in 400G/800G.

Q6: Do I need to upgrade cabling for 400G/800G?
A: Yes, often. OM4/OM5 for short reach; OS2 single-mode for DR/FR/LR.

Q7: Are 400G/800G modules backward compatible with 100G ports?
A: No. Ports must support the same speed.

Q8: How to calculate ROI for upgrades?
A: Factor in power savings, GPU utilization gains, and longer lifespan of higher-speed networks.

Q9: Will 1.6T replace 400G/800G soon?
A: Not immediately. 400G/800G will coexist for at least the next decade.

Q10: Is 800G overkill for SMBs?
A: Yes. SMBs can stick with 100G or 400G.

Conclusion

  • 100G: Still relevant for enterprises and cost-conscious deployments.
  • 400G: Today’s mainstream, essential for cloud and AI pods.
  • 800G: Future-proof choice for hyperscale AI, HPC, and DCI.

The right path depends on scale, workload, and budget. The key is to plan upgrades carefully with end-to-end alignment (NICs, switches, optics, and cabling).

👉 For easier planning, providers like network-switch.com offer complete 100G/400G/800G solutions tested for compatibility, helping you deploy with confidence.

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