How to Migrate from 100G to 400G Data Centers?

With the surge in demand for AI computing power and the expansion of cloud services, European and American data centers are accelerating the migration from 100G to 400G architectures. This upgrade represents not only a leap in bandwidth but also a paradigm shift in network architecture. The following are key migration paths and solutions based on market practices in Europe and the United States.

Migration Background and Market Drivers

The cost and performance inflection point has arrived

400G module prices: By 2024, they will drop to 2-3 times that of 100G modules, while bandwidth will increase 4x, resulting in a significant price-performance advantage.

Exploding Market Demand: TrendForce predicts that global shipments of 400G and higher optical modules will reach 31.9 million units in 2025, a 56.5% annual increase, primarily driven by European and American cloud service providers (AWS, Google, Meta) and demand for AI computing power.

Business scenarios drive upgrades

AI cluster interconnection requires a 400G RoCE network with a latency requirement of less than 0.5μs.

Edge computing nodes need to handle four times the traffic burst, and 100G SR4 cannot meet this requirement.

Migration Path Planning: Four-Phase Progressive Upgrade

Phase 1: Network Architecture Assessment and Compatibility Design

Topology Reconstruction:

Upgrade the traditional three-layer architecture (access-aggregation-core) to a CLOS leaf-spine architecture to eliminate bandwidth bottlenecks.

Reserve ports to support future 800G hybrid networking (e.g., China Telecom has verified 400G/800G wavelength coexistence technology, which can be used as a reference in Europe and the United States).

Optical Layer Compatibility Verification:

Existing fiber infrastructure must support PAM4 modulation (e.g., single-mode fiber OM4/OM5). Transmission distances greater than 500m require the deployment of EDFA amplifiers.

Phase 2: Module and Cable Selection Strategy

Scenario Recommended Solution Advantages

Intra-cabinet interconnection (<3m): 400G AEC active cables. Costs only 30% of optical modules and is 1/73 smaller.

Inter-cabinet interconnection (<500m): 400G SR8/DR4 optical modules. Multimode fiber reduces cabling costs.

Inter-building interconnection (<10km): 400G LR4/ER4 coherent modules. Supports metro DCI interconnection.

Long-haul backbone network: 400G ZR+ coherent modules. Supports 80km without repeaters (e.g., Arelion’s Hamburg-Stockholm line).

Key Innovation:

Swedish operator Arelion uses a hybrid architecture of 1.6T channels and 400G pluggable modules to double the single-wavelength capacity of its Oslo-Copenhagen backbone network, providing a “high-speed channel” for AI data centers.

Phase 3: Power Consumption and Heat Dissipation Optimization

Module-level: Select 400G FR4 modules based on 7nm DSP chips (such as the Eoptosolar solution), keeping power consumption to 8-9W, a 35% reduction compared to earlier versions.

Cabinet-level: Deploy liquid-cooled cabinets (such as Meta’s OCP open architecture) to address the heat dissipation challenge of 400G switches exceeding 15kW per cabinet.

Phase 4: Testing and Phased Rollout

Traffic Scaling Verification:

First migrate 10% of non-critical services (such as backup storage) and monitor bit error rate (BER < 1E-12) and jitter tolerance.

Use the built-in BERT function in intelligent optical modules to achieve fault prediction accuracy exceeding 90%. 

Key Technology Selection and Supplier Ecosystem

Optical Modules:

QSFP-DD 400G FR4: A mainstream form factor, supporting 4x100G PAM4 channels, with a 2km transmission distance of up to 10km;

Coherent 400G ZR+: Ciena and Cisco solutions already support long-haul transmission distances exceeding 1000km (Arelion has verified this).

Copper Cable Alternatives:

In NVIDIA’s GB200 cluster, the ratio of 400G AEC to GPU is 1:1, with 70-80 modules used per cabinet at a cost of only $140 per module (one-third the cost of an optical module).

European and American Supply Chain:

Chipsets: Marvell (low-cost) and Credo (high-performance retimers) dominate the AEC market.

Equipment Vendors: Ciena’s open RLS system and Cisco’s 800G ZR+ modules have been adopted by leading operators.

Migration Implementation: Best Practices

Case 1: Arelion Scandinavia Upgrade

Using the Ciena 6500 RLS platform and 400G pluggable modules, the Oslo-Stockholm-Copenhagen AI Expressway will be completed in Q2 2025, supporting interconnection between supercomputing centers.

Case 2: Meta’s proprietary ASIC architecture

Deploying 400G AECs in a Trn2 chip cluster, with a chip-to-AEC ratio of 1:1.5, reduces power consumption by 20% through DSP streamlining.

Future Evolution: Smooth Transition to 800G/1.6T

Hybrid-Rate Networking:

China Telecom has achieved 400G/800G wavelength coexistence. European and American operators can reuse existing ROADM networks for gradual upgrades.

Technology Development Directions:

CPO Co-packaged Optics: Shortens the distance between the optical engine and ASIC to 5mm, reducing system power consumption (e.g., NVIDIA’s GB300 is already planned);

LPO Linear Drive: Eliminates the DSP chip, reducing power consumption by 20% in short-reach scenarios.

Summary

The 100G to 400G migration in European and American data centers requires a core strategy of “optical-copper synergy”:

Optical: Utilize 400G ZR+/FR4 modules for backbone/metro areas, complementing the CLOS architecture reconstruction;

Copper: Prioritize AEC within the cabinet to reduce costs and complement optical modules.

With AWS and Google planning to mainstream 800G by 2026, current 400G upgrades must ensure rate compatibility. Only through a combined strategy of module selection, topology optimization, and phased verification can a cost-effective and lossless migration be achieved.