100G DAC has become an indispensable connectivity solution in high-speed data centers and HPC networks. With their high bandwidth, low latency, and cost-effectiveness, they have become the preferred choice for short-distance connections between switches, servers, and other devices. This article will provide a detailed understanding of what a 100G DAC is, its performance, and application scenarios, helping you understand whether you need a 100G DAC when deploying your network.

What is a 100G DAC

A 100G DAC is a copper cable with non-removable QSFP28 connectors at both ends, primarily used for short-distance data transmission. It consists of high-quality coaxial copper wire and supports parallel transmission of four 25G channels, achieving a total rate of 100Gbps. Its outer sheath has a shielding layer, effectively resisting electromagnetic interference and preventing signal transmission from being disrupted.

Unlike optical modules, the DAC does not involve photoelectric conversion; the signal is transmitted directly in electrical form, resulting in extremely low latency and lower power consumption. The transmission distance of a 100G DAC is typically within 3 meters, while 6COM can provide 100G DAC up to 5 meters long.

Types of 100G DAC

100G DAC are generally divided into two types: 

Passive DAC: Passive DAC have no internal signal amplification or equalization circuitry, relying entirely on the electrical compensation capabilities of the device ports. They are suitable for short-distance connections of 1-3 meters, such as interconnecting servers within the same rack to a TOR switch.

Active DAC: Active DAC integrates equalization or retiming chips at both ends of the cable to enhance signal integrity. They can achieve connection distances of up to 5-7 meters and are commonly used for inter-rack interconnects.

Because passive DAC lack internal signal amplification or equalization circuitry, their power consumption is almost negligible compared to active DAC, resulting in lower costs. You can choose based on your specific link length.

Performance Advantages of 100G DAC

While price is one reason for the widespread adoption of DAC, its advantages extend far beyond that.

Low Latency: DAC eliminates the photoelectric conversion stage, resulting in latency typically only a few nanoseconds. This offers significant cost-effectiveness for latency-sensitive applications such as financial transactions or AI clusters.

Low Power Consumption: Compared to 100G optical modules, passive DAC consume negligible power because they require no photoelectric conversion or signal amplification. Even an active DAC consumes only about 0.5W.

High Reliability: Because DAC lack complex optical components, and the copper cable structure is more robust than fiber optics, they are more durable than modules and patch cords in long-term operation.

Plug and Play: DAC require no additional configuration; compatibility is confirmed at the time of purchase, facilitating deployment and subsequent maintenance.

How to Choose the Right 100G DAC

When selecting a suitable DAC, transmission distance, device compatibility, and cabling flexibility need to be considered comprehensively.

For transmission distances less than 5m: Passive DAC are preferred due to their lowest cost and optimal performance.

For transmission distances between 5 and 7m: Active DAC can be chosen because they can compensate for signal loss and support longer transmission distances.

For transmission distances exceeding 7m: 100G AOC or optical module connection solutions should be considered, as DAC typically only supports connections within 7 meters.

Select a compatible DAC based on the equipment being used: Different manufacturers (such as Cisco, Arista, and Juniper) have specific requirements for EEPROM information. You need to select a compatible DAC when ordering; otherwise, connection problems may occur.

Minimum bending radius and cabling density: When deploying DAC in high-density environments, the minimum bending radius and volume occupied by the DAC need to be considered. Excessive bending can degrade signal transmission quality or even damage the product. Excessive density can also cause poor air circulation, leading to heat dissipation problems and interference with signal transmission.

Applications of 100G DAC

Top-of-Rack (TOR) connectivity: DAC are frequently used in TOR connections. With switches deployed at the top of the server rack, using DAC offers greater cost-effectiveness and ease of maintenance.

In-Rack Switch Interconnection: Switches within a rack can also be interconnected using DAC because they are cheaper and consume less power than modular interconnect solutions.

In AI computing clusters, hyperconverged infrastructure, and hyperscale data centers, 100G DAC is also a common solution for interconnecting GPU nodes.

Conclusion

100G DAC, with their low cost, low latency, high reliability, and ease of deployment, occupy a central position in modern data centers and high-performance network architectures. Understanding their characteristics and applicable scope not only helps optimize network performance but also significantly reduces overall construction and operation costs. In the era of high-speed, low-power data centers, the proper use of 100G DAC will be a key step for enterprises to achieve efficient interconnectivity.