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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:
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:
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
800G Optical Modules
Long-Reach Solutions
These products enable scalable AI networking across data halls, campuses, and metropolitan regions.
DAC vs AOC vs Optical Modules: A Practical Comparison
| Feature | DAC | AOC | Optical Modules |
|---|---|---|---|
| Cost | Lowest | Medium | Highest |
| Power Consumption | Lowest | Medium | Medium-High |
| Latency | Lowest | Very Low | Very Low |
| Cable Weight | Heavy | Lightweight | Fiber-Based |
| Maintenance | Replace Entire Cable | Replace Entire Cable | Replace Module Individually |
| Scalability | Limited | Moderate | Excellent |
| Structured Cabling | No | No | Yes |
| Distance | 0.5-5m | 5-100m | 100m-80km+ |
| AI Deployment Scale | Rack-Level | Cluster-Level | Data Center-Level |
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.
Frequently Asked Questions (FAQ)
Q1. What is the difference between DAC, AOC, and optical modules?
Answer: DAC, AOC, and optical modules are three common solutions for high-speed data center interconnects. DAC (Direct Attach Copper) uses copper cables and is optimized for short-distance, low-cost connections. AOC (Active Optical Cable) integrates optical fiber and transceiver components to support longer distances with better flexibility. Optical modules use pluggable transceivers with fiber cables, providing the highest scalability and supporting long-distance transmission for advanced data center networks.
Q2. Which interconnect solution is best for AI data centers: DAC, AOC, or optical modules?
Answer: The best solution depends on the network layer and transmission distance. DAC cables are ideal for short connections between GPU servers and ToR switches due to their low power consumption and cost efficiency. AOC cables are suitable for medium-distance connections inside AI clusters, while optical modules are preferred for large-scale AI fabrics, spine networks, and data center interconnects requiring higher bandwidth and scalability.
Q3. Why are DAC cables widely used in AI GPU clusters?
Answer: DAC cables are widely used in AI GPU clusters because they provide ultra-low latency, low power consumption, and cost-effective high-speed connectivity. They are commonly deployed for GPU server-to-switch connections within racks or adjacent racks, especially in 400G and 800G AI infrastructure where minimizing power consumption and deployment costs is critical.
Q4. What are the advantages of AOC cables compared with DAC cables?
Answer: AOC cables offer longer transmission distances, lighter weight, better airflow performance, and improved electromagnetic interference resistance compared with DAC cables. They are suitable for rack-to-rack and cluster-level connections where cable management, flexibility, and installation distance are more important than the lowest cost.
Q5. When should I choose optical modules instead of DAC or AOC?
Answer: Optical modules are the preferred choice when networks require long transmission distances, high bandwidth scalability, and flexible deployment. They are commonly used in AI data center spine-leaf architectures, hyperscale cloud networks, DCI (Data Center Interconnect), and telecom infrastructure where 400G, 800G, and future 1.6T optical connectivity are required.
Q6. What is the transmission distance difference between DAC, AOC, and optical modules?
Answer: DAC cables are typically used for short-distance connections from around 0.5m to several meters. AOC cables can extend transmission distances to tens of meters or more while maintaining simple deployment. Optical modules provide the widest transmission range, from short-reach 100m links to long-distance connections spanning multiple kilometers depending on the transceiver type.
Q7. Should I use DAC, AOC, or optical modules for 800G AI networking?
Answer: For 800G AI networking, different solutions are used in different network layers. 800G DAC is suitable for short GPU server connections requiring low power and low cost. 800G AOC is used for medium-distance AI cluster connections with improved flexibility. 800G OSFP and QSFP-DD optical modules are typically deployed in leaf-spine networks and large-scale AI fabrics requiring maximum bandwidth density and scalability.
Q8. Can DAC, AOC, and optical modules be used together in the same AI data center?
Answer: Yes. Modern AI data centers typically use a hybrid interconnect architecture combining DAC, AOC, and optical modules. DAC is commonly used for GPU server-to-ToR connections, AOC for medium-distance rack and cluster connections, and optical modules for spine, backbone, and DCI links. This approach provides the best balance between performance, power efficiency, cost, and scalability.
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