How to Choose Between 10G and 400G DAC and AOC Cables?

With the surging demand for data center interconnects, DAC and AOC cables play a pivotal role as the primary solutions for intra-rack and inter-rack connectivity. In this article, YXFiber analyzes selection strategies for 10G to 400G scenarios and presents a practical implementation plan.

1. What are DAC and AOC cables?

1.1 DAC (Direct Attach Copper)

A DAC is a fixed assembly that integrates copper cabling with connectors at both ends. Signals are transmitted directly through the copper cable in electrical form. DACs can be categorized into passive DACs and active ACCs. Passive DACs contain no active electronic components and have near-zero power consumption, making them the most cost-effective choice for short-range connections. Active ACCs feature built-in signal conditioning chips that extend the transmission distance to 7–10 meters, albeit with slightly higher power consumption.

1.2 AOC (Active Optical Cable)

AOCs utilize optical fibers for signal transmission and integrate photoelectric conversion modules at both ends. While they appear identical to DACs from the perspective of switch or server interfaces, the signals actually undergo an "electrical-to-optical-to-electrical" conversion process. Utilizing optical fiber as the transmission medium, AOCs offer advantages such as light weight, high flexibility, and immunity to electromagnetic interference.

2. Key factors influencing selection

2.1 Transmission distance

For 1G and 10G DACs, the maximum transmission distance is 7 meters; for 25G, 40G, and 100G DACs, it is 5 meters; and for 200G and 400G DACs, it is 3 meters. The maximum transmission distance is 150 meters for 10G AOCs; 100 meters for 25G, 40G, 100G, 200G, and 400G AOCs; and 50 meters for 40G QSFP+, 100G QSFP28, and 200G QSFP56 breakout AOCs.

2.2 Total Cost of Ownership (TCO)

Regarding procurement costs, DAC cables offer a distinct advantage in short-reach scenarios; at the same 400G data rate, 400G DACs are less expensive than 400G AOCs and 400G optical transceivers. Beyond the initial purchase price, hidden costs must also be considered. In terms of power consumption, AOC cables integrate internal photoelectric conversion components, resulting in slightly higher power usage compared to passive DACs. Regarding cabling, AOCs utilize lightweight, flexible optical fibers, allowing for cabling densities three to five times higher than that of DACs.

2.3 Operations, Maintenance, and Reliability

The advantage of DACs lies in their purely physical connection, which ensures an extremely low failure rate and plug-and-play functionality; additionally, connectors can be replaced individually without the need for fiber cleaning or inspection tools.

AOCs offer advantages such as thin, flexible fiber cabling suitable for high-density racks, complete immunity to electromagnetic interference (allowing them to be routed alongside power cables), and light weight, which reduces strain on connectors.

3. Selection Guide by Data Rate

3.110G/25G Scenarios (ToR Access Layer)

Currently, 10G and 25G are the most mature data rates for the data center access layer. They cover the vast majority of intra-rack interconnects, offer excellent cost-effectiveness, and support transmission distances of up to 7 meters.

Typical deployments involve connections between servers and ToR switches. Passive DACs are the primary choice for interconnecting devices within the same rack, balancing low power consumption with low costs. For medium-to-long-distance connections in enterprise campuses or commercial buildings—such as cabling across floors or between server rooms—AOC cables are preferred due to their electromagnetic interference immunity, supporting transmission distances of tens to over a hundred meters.

3.2 40G/100G Scenarios (Spine-Leaf Architecture)

In Spine-Leaf architectures, DAC cables are the preferred choice for short-reach connections (under 5 meters). For medium-reach connections between racks or across rows, DAC cables are suitable for distances of 5–10 meters, while AOC cables are suitable for 10–30 meters. For medium-to-long-reach connections across racks or rows exceeding 30 meters, AOC cables are the appropriate choice.

3.3 400G Scenarios (Hyperscale Data Center Core)

For short-range connections (under 3 meters) within 400G data center racks, 400G passive DACs represent the optimal solution. For longer-range connections, 400G AOCs support transmission distances of up to 100 meters, covering the vast majority of Leaf-Spine interconnect scenarios.

Conclusion

Throughout the evolution from 10G to 400G, DAC cables have consistently remained the most cost-effective choice for ultra-short-range, in-rack connectivity, firmly dominating the short-range sector. Meanwhile, AOCs—leveraging the lightweight, slender, and flexible nature of optical fiber, as well as its immunity to electromagnetic interference and long-distance transmission capabilities—dominate medium- to long-range connectivity across cabinets and rows. Together, these two technologies offer engineers more refined options for selecting the right solution.