The rapid growth of Artificial Intelligence (AI), Large Language Models (LLMs), and high-performance computing (HPC) has dramatically increased the demand for high-speed networking inside modern data centers.

Today's AI clusters may contain hundreds or even thousands of GPUs connected through high-bandwidth Ethernet or InfiniBand fabrics. While GPUs provide the computing power, network interconnects determine how efficiently those GPUs can communicate.

Choosing the right connectivity technology is therefore critical.

The three most common options are:

• Direct Attach Cables (DAC)

• Active Optical Cables (AOC)

• Optical Transceivers

Each solution offers unique advantages depending on distance, deployment architecture, budget, and operational requirements.

Why AI Clusters Require High-Performance Interconnects

Unlike traditional enterprise networks, AI workloads generate enormous east-west traffic.

Examples include:

• Distributed AI training

• AllReduce communication

• Expert routing in MoE models

• Parameter synchronization

• Storage checkpoint transfers

• GPU-to-GPU communication

In these environments, network performance directly impacts:

• GPU utilization

• Training completion time

• Cluster scalability

• Energy efficiency

• Overall infrastructure ROI

Even a small increase in latency or packet loss can affect thousands of GPUs simultaneously.

This is why selecting the right interconnect solution has become a strategic decision for AI infrastructure operators.

Understanding the Three Connectivity Options

1. DAC (Direct Attach Cable)

DAC is a copper-based solution with high-speed connectors permanently attached at both ends.

Key Advantages

• Lowest purchase cost

• Lowest power consumption

• Extremely low latency

• No optical conversion required

• Easy deployment

Limitations

• Limited transmission distance

• Heavier cable bundles

• Difficult cable management in large deployments

Typical Distance

0.5m to 5m

Best AI Applications

• GPU server to ToR switch

• In-rack GPU connectivity

• Switch-to-switch connections within the same rack

For these scenarios, C-LIGHT provides:

• 25G SFP28 DAC

• 100G QSFP28 DAC

• 200G QSFP56 DAC

• 400G QSFP-DD DAC

• 400G OSFP DAC

• 800G OSFP DAC

• 800G QSFP-DD DAC

These products deliver excellent power efficiency and cost savings for high-density AI racks.

2. AOC (Active Optical Cable)

AOC integrates optical transceivers and fiber into a single cable assembly.

It combines the simplicity of DAC with the transmission advantages of fiber optics.

Key Advantages

• Longer transmission distances

• Lightweight cable management

• Reduced airflow obstruction

• Strong EMI immunity

• Simple plug-and-play deployment

Limitations

• Higher cost than DAC

• Entire cable must be replaced if damaged

Typical Distance

5m to 100m

Best AI Applications

• Cross-rack GPU clusters

• Leaf-to-Leaf connections

• High-density AI server rooms

C-LIGHT's AOC portfolio includes:

• 100G QSFP28 AOC

• 200G QSFP56 AOC

• 400G QSFP-DD AOC

• 400G OSFP AOC

• 800G OSFP AOC

• 800G QSFP-DD AOC

These solutions are widely used in AI fabrics where reducing cable weight and improving airflow are critical.

3. Optical Transceivers

Optical transceivers provide the highest level of flexibility and scalability.

Unlike AOCs, optical modules and fiber jumpers are separate components, making maintenance easier and supporting structured cabling architectures.

Key Advantages

• Long transmission distances

• Flexible deployment

• Easy replacement and maintenance

• Supports structured cabling

• Ideal for large-scale AI fabrics

Limitations

• Higher upfront investment

• Higher power consumption than DAC

Typical Distance

100m to 80km+

Best AI Applications

• Leaf-Spine networks

• Data Center Interconnect (DCI)

• Multi-building AI campuses

• Long-distance GPU cluster expansion

C-LIGHT offers a complete optical networking portfolio including:

400G Optical Modules

• 400G QSFP-DD SR8

• 400G QSFP-DD DR4

• 400G QSFP-DD FR4

• 400G QSFP-DD LR4

800G Optical Modules

• 800G OSFP 2DR4

• 800G OSFP 2FR4

• 800G QSFP-DD 2DR4

• 800G QSFP-DD 2FR4

Long-Reach Solutions

• 100G DWDM Transceivers

• 400G DWDM Solutions

• CWDM/DWDM MUX DEMUX Platforms

These products enable scalable AI networking across data halls, campuses, and metropolitan regions.

DAC vs AOC vs Optical Modules: A Practical Comparison

How AI Data Centers Actually Choose

Most AI operators do not rely on a single technology.

Instead, they deploy a combination of all three.

Inside the Rack

Use DAC.

The short distance makes DAC the most economical and energy-efficient option.

Between Racks

Use AOC.

The lightweight design simplifies deployment while supporting longer distances.

Across Data Halls or Buildings

Use Optical Transceivers.

They provide the flexibility, maintainability, and scalability required for large AI infrastructures.

A common deployment strategy looks like this:

• GPU Server → ToR Switch → DAC

• ToR Switch → Leaf Switch → AOC

• Leaf Switch → Spine Switch → Optical Modules

• Building-to-Building → DWDM Solutions

This hybrid approach balances performance, cost, and operational efficiency.

The Impact of 400G and 800G AI Networking

Modern AI platforms powered by NVIDIA H100, H200, and Blackwell GPUs are accelerating the transition to 400G and 800G networking.

As AI models continue to scale, network requirements include:

• Higher bandwidth

• Lower latency

• Better congestion control

• Greater energy efficiency

C-LIGHT addresses these requirements with a comprehensive AI networking portfolio covering:

400G Solutions

• 400G DAC

• 400G AOC

• 400G DR4

• 400G FR4

• 400G LR4

800G Solutions

• 800G DAC

• 800G AOC

• 800G DR8

• 800G 2×FR4

These products are designed to support Ethernet and InfiniBand AI fabrics while enabling future migration toward 1.6T networking.

Conclusion

There is no single "best" interconnect solution for AI clusters.

The optimal choice depends on distance, architecture, scalability requirements, and operational objectives.

A simple rule of thumb is:

Choose DAC for short-distance, cost-sensitive deployments.

Choose AOC for medium-distance, high-density AI networking.

Choose optical transceivers when scalability, structured cabling, and long-distance connectivity are required.

In practice, the most successful AI data centers combine all three technologies to create a balanced, high-performance network architecture.

With a complete portfolio of DAC cables, AOC solutions, optical transceivers, and WDM platforms, C-LIGHT helps customers build reliable, scalable, and future-ready AI networking infrastructures.