Foreword

In the wave of digitalization, data centers bear the heavy responsibility of massive data processing, storage, and transmission, becoming the core hub of the information age. For internal data center connections and short-distance interconnection scenarios, high-speed copper cable technology is crucial. Among these, passive Direct Attach Cables (DACs) stand out from many transmission solutions due to their unique advantages. They do not require external power, transmitting signals directly through copper cables, making them economical and efficient. This perfectly aligns with the urgent need for short-distance, high-speed, and low-power consumption transmission as data centers expand, providing strong support for fast and stable data exchange between devices.

Technical Composition and Characteristics of Passive DACs

Basic Attributes

Passive DACs use a combination of silver-plated copper conductors and foamed insulation core wires. Silver-plated copper conductors have excellent conductivity, effectively reducing resistance loss and ensuring signal integrity; foamed insulation core wires act as isolation, reducing signal crosstalk and improving transmission performance. During operation, they convert digital signals into analog signals for transmission through copper cables. The transmitting device converts digital signals into analog electrical signals suitable for copper cables, which are then transmitted through the copper cable to the receiving end and converted back into digital signals for device processing.

Advantages

Passive DACs offer significant cost-effectiveness, being much cheaper than active transmission technologies. Large-scale deployment can greatly save costs, a clear advantage when data centers connect numerous servers and switches. They have extremely low power consumption; for example, a 25G specification typically consumes less than 0.1W, aligning with the green and energy-saving operational philosophy of data centers. Their simple and reliable structure, with an integrated module head and copper cable, reduces compatibility issues and lowers the probability of failure, making them suitable for data center scenarios with high stability requirements. Furthermore, they have high mechanical stress tolerance, facilitating quick installation and connection during data center construction or equipment upgrades, without complex debugging, thus shortening deployment time.

Disadvantages

Passive DACs have limited transmission distance, generally effective within 10 meters, making them unsuitable for cross-room or long-distance equipment connections. They are susceptible to electromagnetic interference; in high-interference environments, signals can easily be distorted, requiring additional shielding measures, which increases deployment cost and complexity. At the same time, they are not suitable for frequent bending or complex cabling, as frequent bending can damage the internal structure of the copper cable, and complex cabling can easily degrade transmission performance due to cable interference.

Passive DAC: Efficient Interconnection Practices in Diverse Scenarios

Short-Distance Interconnection in Data Centers

In data centers, the connection distance between servers and switches is often 1-5 meters. Passive DACs become the preferred choice due to their low cost and high reliability. A large number of such connections build an efficient data transmission network, ensuring stable operation of data centers. In AI training clusters, computing and storage nodes require rapid transmission of massive data, passive DACs provide high-speed and stable transmission over short distances, powerfully supporting AI training.

Intra-Board and Intra-Rack Connections

In intra-board interconnections, such as high-speed signal transmission between different chips on a computer motherboard, passive DACs can ensure fast and accurate signal delivery, improving motherboard performance. Within server racks, they are also used to connect different equipment modules, achieving efficient communication between devices within the rack.

Passive DAC vs. Other Technologies: A Multi-Dimensional Performance Analysis

Compared to Active Technologies (ACC, AEC)

Passive DACs have a significant cost advantage, being much lower in price than active technologies, but their transmission distance and signal integrity are inferior to active technologies. Active technologies can support longer transmissions and have stronger signal processing capabilities, but they require additional power and have higher power consumption. In energy-sensitive scenarios, the low power consumption characteristic of passive DACs is more competitive.

Compared to AOC (Active Optical Cables)

AOCs have a long transmission distance, while passive DACs are shorter, generally within 10 meters. However, in short-distance and cost-sensitive, high-cost-performance scenarios, passive DACs perform excellently. In terms of weight and volume, AOCs are lighter and more compact, facilitating cabling and transportation, while passive DACs are relatively larger due to their copper material, posing some inconvenience.

Future Development and Challenges

Technological Optimization

Researchers and engineers are committed to improving the signal integrity and extending the transmission distance of passive DACs through material and design optimization, such as developing new copper cable materials to reduce resistance and signal loss, and optimizing cable structures to reduce crosstalk. To address electromagnetic interference, measures include increasing shielding layer design, adopting advanced shielding materials and processes, and enhancing anti-interference capabilities to ensure stable operation in complex electromagnetic environments.

Market Demand

With the continuous expansion of data centers and AI computing clusters, the demand for short-distance high-speed connections is strong, providing broad space for the development of passive DACs. Facing the continuous iteration and updates of hardware architectures, passive DACs need continuous optimization to meet the higher requirements of new-generation data center architectures for device connection density, speed, and reliability, maintaining competitiveness in the field of short-distance interconnection.

Conclusion

Passive DACs, with their advantages of high cost-effectiveness, low power consumption, and flexible deployment, hold an important position in scenarios such as short-distance interconnection within data centers. Despite facing challenges like transmission distance and electromagnetic interference, with technological advancements, through measures such as improving signal integrity and enhancing anti-interference capabilities, they are expected to continue playing a key role in the future, contributing to the efficient operation of data centers and the development of information technology.