Those who work in data center, switch maintenance, and GPU cluster deployment are often confused by two types of cables: DAC Passive Copper Cable and ACC Active Copper Cable. They look almost identical, have completely interchangeable interfaces, and are both high-speed copper cables, leading many to choose based on intuition alone, resulting in:

1)Excessive signal attenuation and packet loss due to link jitter in high-speed, long-distance interconnection scenarios

2)Port online error, unstable link negotiation

3)Insufficient matching of equipment selection leads to waste of resources and construction rework costs

Today, I'll use this article to thoroughly explain the differences between DAC and ACC, how to distinguish them, and the selection scenarios!

Ⅰ.Core Principles and Technical Characteristics

DAC (Passive Direct Attach Cable)

The DAC cable has no chips, circuits, or signal processing units. Both ends are just standardized metal shells. It directly transmits high-speed electrical signals using high-purity copper differential cables. There is no signal amplification, equalization, or shaping processing throughout the entire process. It is a purely passive transmission medium.

Technical Characteristics:

1. Zero power consumption and extremely low transmission latency, suitable for ultra-low latency computing scenarios.

2. Simple structure, no electronic components, near-zero failure rate, and extremely high stability.

3. Mature mass production, affordable cost , and compatibility with all brands of data communication equipment.

4. Lacks signal compensation capability; transmission attenuation is significant in high-speed scenarios, limiting transmission distance.

ACC (Active Copper Cable)

Based on traditional copper cables, the ACC integrates a Redriver analog equalizer chip at the connector end , which can amplify the gain, compensate for the loss, and equalize the waveform of high-speed electrical signals that are attenuated and distorted during transmission, effectively improving the signal integrity of high-speed links and breaking through the transmission distance limitations of DAC.

Technical Characteristics:

1. Excellent signal compensation capability; transmission distance at the same data rate is far superior to that of passive DACs.

2. Pure electrical signal transmission, with no photoelectric conversion delay, resulting in significantly better delay performance than AOC active optical cables.

3. The interface protocol and physical form are fully compatible with the DAC, and the adapter can be directly replaced.

4. Requires port power supply, has fixed power consumption, and active chips are at risk of device failure.

5. Only supports analog signal compensation, lacks CDR clock reconstruction capability, and cannot completely eliminate high-speed jitter and inter-symbol interference.

Ⅱ.Rapid Engineering Differentiation: Physical Identification + Equipment Verification

1) Physical Appearance Identification (Rapid On-Site Identification)

DAC Passive Copper Cable: Lightweight, Slim Housing; Neat Construction

The module shells at both ends have uniform thickness, the outgoing ports have no injection-molded expansion structure, the entire cable has uniform thickness, the overall weight is light, there are no protruding encapsulation areas, and there are no internal electronic component encapsulations.

ACC Active Copper Cable: Thicker jacket, localized bulges

The single-ended or dual-ended module housing is significantly thickened and raised, with reserved space for PCB and chip packaging inside. The connector weight and volume are significantly larger than those of a DAC of the same specification, and the tail injection molding structure is thicker and heavier.

2) Cable Label Recognition (100% Accurate Identification)

Passive DAC: Passive, Passive Copper, Passive Straight-Through Cable

Active ACC: ACC, Active Copper, Redriver, Active Balancing Copper, Powered Copper

3) Equipment Background Verification (Standardized Operation and Maintenance Verification)

By querying optical module information through switch and server ports, the media type can be accurately determined.

DAC: Device identification type is Passive Copper

ACC: Device identification type is Active/Redriver Copper

Significant differences in characteristics under power-off conditions: The DAC is a purely physical medium, and power-off does not affect the link conduction; the ACC relies on the port power supply driver chip, and the signal compensation function fails after power-off, and the link goes down directly.

Ⅲ.Comparison of Core Parameters

Ⅳ.Engineering Standardization Selection Specification (100 Gb/s PAM4 Signals Per Lane))

1) Distance ≤ 2m, AI low-latency cluster, cost-effective and stable → DAC is a must

With servers located close to each other in the rack, GPUs hop short, and TORs connected nearby, it is the absolute home ground for DACs.

2) For distances of 2-5m, server rack spanning multiple floors, and where fiber optic cables are not preferred, ACC is the preferred option.

It solves the DAC distance bottleneck while retaining the low latency advantage of the electrical port, offering extremely high cost-effectiveness.

3) For distances > 5m, high stability requirements, and cross-rack cabling → directly use AOC/AEC

The ACC compensation capability is limited, and it is prone to jitter and bit errors in long-distance, high-speed scenarios.

That concludes this article! ETU-LINK, as a professional platform offering comprehensive optical network products and services, can provide you with stable, reliable, cost-effective, and efficient optical modules and overall network transmission solutions. If you would like to learn more about optical communication products, please send us a private message or leave a comment. We will reply to you as soon as possible after receiving your inquiry!