As modern networks move from 100G to 400G and even 800G Ethernet, engineers are redesigning short-reach interconnect architectures inside racks and between racks. High-speed data center cables have become a critical part of network infrastructure.

Ten years ago, passive copper cables solved the majority of rack connectivity issues. Today, with 112G PAM4 signaling, copper channels are operating much closer to their physical limits.

Network architects now have four major options for short-distance high-speed connections:

• DAC (Direct Attach Copper)
• ACC (Active Copper Cable with redriver)
• AEC (Active Electrical Cable with retimer)
• AOC (Active Optical Cable)

Each technology addresses different challenges related to signal integrity, cable reach, rack density, and total cost of ownership.

This guide explains how these data center cables work and how to choose the best solution for modern 400G and 800G data center networks.

What Are the Differences Between DAC, ACC, AEC, and AOC?

The primary difference between these cable types lies in how they handle signal integrity and transmission distance.  

In simpler terms:

• DAC depends entirely on the copper channel.
• ACC slightly amplifies the signal.
• AEC regenerates and retimes the signal.
• AOC converts the signal into light.

Selecting the right data center cable depends mainly on reach requirements and available signal margin.

Why 400G and 800G Networks Make Cable Selection More Difficult

Modern Ethernet networks rely on PAM4 modulation to achieve higher bandwidth.

Examples:

• 400G Ethernet → 4 × 112G PAM4 channels
• 800G Ethernet → 8 × 112G or 4 × 224G lanes

PAM4 allows significantly higher throughput compared with earlier NRZ signaling. However, it also introduces new challenges for 400G cables and high-speed data center cables:

• Higher insertion loss sensitivity
• Smaller eye diagrams
• Increased jitter sensitivity
• Reduced signal margins

These factors make cable quality and signal conditioning far more important in modern data center cable design.

Direct Attach Copper (DAC): Simple and Cost-Effective

DAC cables are the simplest form of high-speed data center cable. They are passive copper wires without active electronics.

Signal quality is entirely dependent on the physical cable construction:

• copper conductor size
• insulation materials and shielding
• cable length

Because there are no active components, DAC cables provide two significant advantages:

• lowest cost per port
• lowest power consumption

400G DAC Cable Length Limit

In modern 400G deployments, passive copper cables are often restricted to short distances.

Typical practical ranges:

• 1–2 meters → stable
• 2–3 meters → near the limit
• 3 meters → signal margin decreases rapidly

To maintain signal integrity at higher speeds, manufacturers increase conductor diameter.

Example:

Thicker cables can create challenges in high-density racks, such as:

• reduced airflow
• tighter bend radius
• difficult cable management

When Is DAC the Best Data Center Cable?

DAC is typically the best option when:

• connection distance is under 2 meters
• connections remain within a single rack
• cost per port is critical
• power consumption must be extremely low

For short connections between servers and a top-of-rack switch, DAC cables remain one of the most widely used data center cables.

Active Copper Cable (ACC): Extending Copper Reach

Active Copper Cables (ACC) provide limited signal conditioning.

ACC integrates a linear redriver chip, which compensates for high-frequency loss in copper channels.

The redriver performs:

• signal amplification
• equalization
• channel compensation

However, it does not fully restore the signal. There is no:

• clock recovery
• retiming
• full signal regeneration

ACC Distance Capabilities

In practice, ACC can extend the reach of passive copper cables.

Typical ranges for 400G cables:

• 3–5 meters

This makes ACC useful when links exceed passive copper limits but do not require full signal retiming.

AEC (Active Electrical Cable): Retimed Copper Interconnect

AEC cables use a more advanced active copper architecture.

Instead of a redriver, AEC integrates:

• retimer
• clock data recovery (CDR)

This allows the signal to be fully regenerated before leaving the cable.

Key benefits include:

• restored clock timing
• improved eye diagram
• stable bit error rate (BER)

AEC Cable Distance

AEC cables typically support:

• ~7 meters at 400G

This makes AEC well suited for structured rack-to-rack connections within the same row.

AEC is increasingly used in AI clusters and high-density computing environments, where hundreds of GPU nodes must be connected across short distances.

AOC (Active Optical Cable): Optical Data Center Cables

AOC cables convert electrical signals into optical signals.

Each end of the cable contains an optical transceiver that performs electrical-to-optical conversion.

Because signals travel through fiber instead of copper, optical communication avoids many electrical limitations.

Typical reach:

• 10–100 meters

Advantages of AOC Cables

AOC offers several benefits for longer-distance data center cables:

• longer transmission reach
• lightweight and flexible cabling
• immunity to electromagnetic interference
• easier routing in dense environments

Limitations of AOC

Optical solutions also involve trade-offs:

• higher cost
• higher power consumption
• optical module lifecycle limitations

If the optical module fails, the entire cable assembly must be replaced.

For distances greater than roughly 7–10 meters, optical links such as AOC cables become the preferred solution.

What Cable Type Is Best for AI Data Centers?

Large AI data centers introduce new infrastructure challenges.

Compared with traditional cloud workloads, AI clusters require:

• extremely high port density
• massive east-west traffic
• tightly packed racks
• large numbers of short connections

Cable diameter and airflow become increasingly important.

In many modern AI deployments:

• DAC is used for extremely short connections
• AEC is preferred for structured short-reach links
• AOC is used for longer rack-to-rack connections

Practical 400G Cable Selection Guide

The following guidelines apply to most 400G data center networks.

Actual selection should also consider:

• rack density
• airflow limitations
• power budget
• long-term operational costs

FAQ: AEC vs DAC and Other Data Center Cable Questions

What is the difference between AEC and DAC cables?

DAC cables are passive and rely entirely on the copper channel. AEC cables include retimer chips that regenerate the signal, enabling longer reach and better signal integrity.

Is AEC better than DAC?

Not always. DAC cables are cheaper and consume less power, while AEC cables provide better signal integrity and longer reach.

What is the maximum length of a 400G DAC cable?

Most modern 400G DAC cables are limited to approximately 3 meters due to signal loss in copper channels.

Why are AEC cables becoming more popular?

AEC cables offer an optimal balance between copper cable cost and signal integrity, making them well suited for short-range high-speed connectivity in AI data centers.

Final Thoughts on Data Center Cables

There is no single cable technology that works best in every situation.

Each data center cable type solves a different physical constraint:

• DAC delivers the lowest cost for extremely short connections.
• ACC slightly extends copper reach.
• AEC improves signal integrity for structured short-distance links.
• AOC enables longer connections using optical transmission.

As 400G and 800G networking continues to expand, active signal conditioning will play an increasingly important role.

Understanding the strengths and limitations of each cable type helps engineers design data center networks that balance performance, density, and cost.

Need Help Choosing the Right Data Center Cable?

Designing modern 400G and 800G networks requires balancing distance, signal integrity, power consumption, and deployment density. Whether your architecture relies on DAC, ACC, AEC, or AOC cables, selecting the right interconnect can significantly impact performance and scalability.

Farsince provides a full range of high-speed data center cable solutions for AI clusters, hyperscale infrastructure, and enterprise networks.

👉 Contact our engineering team to discuss your 400G / 800G connectivity requirements.

Author

Franck Yan
Founder | Farsince Connectivity Solutions

Franck Yan is the founder of Farsince and has more than 13 years of experience in the cable and connectivity industry, working closely with global customers on data center, industrial, and network connectivity solutions.