DAC vs AOC vs AEC vs ACC: Choosing the right high-speed interconnect for 400G/800G networks

Interconnect Options at a Glance

The right interconnect depends on the physical link requirement, platform, power budget, thermal environment, and deployment goal. Axiom Engineering evaluates these options by link rather than applying one cable type across an entire network.

DACs

Direct Attached Cables, or DACs, are cables with transceiver-style connectors or endpoints. While they use the same form factors as optical transceivers, their transmission medium is copper.

DACs are passive, meaning they do not include active components like a typical transceiver. They are available across multiple data rates and form factors, from 10G SFP+ through 800G OSFP.

In addition to point-to-point cable configurations, DACs are also available as breakout cables. These breakout cables split a higher data rate connection into lower data rate lanes, such as 40G to 4 x 10G or 100G to 4 x 25G. Breakout configurations are useful for connections from a Top-of-Rack switch to multiple servers or network interface cards.

Because copper is the transmission medium, the maximum length a DAC supports varies by data rate due to interference and crosstalk at higher transmission speeds. For data rates greater than 400G, a DAC will typically have a maximum length around 3 meters.

AOCs

Active Optical Cables, or AOCs, are the most similar to a standard fiber optic connection. They use optical fiber as the transmission medium and convert electrical signals into optical signals, similar to a standard transceiver.

Unlike a standard pluggable transceiver, the fiber cable is permanently attached. AOCs are often less expensive than a pair of separate fiber optic transceivers because the optical components are integrated with the cable assembly.

AOCs, like DACs, are available in multiple data rates and form factors. They are also available as breakout cables.

Active Optical Cables support longer lengths than copper-based options, often around 100 meters depending on data rate and platform. They are not always used for the full distance because routing a cable with an attached transceiver housing can create deployment challenges.

ACCs

Active Copper Cables, or ACCs, are a variation of traditional DACs. Like DACs, ACCs use copper cabling as the transmission medium. Unlike passive DACs, ACCs include an active signal driver or equalizer.

These active components compensate for losses caused by transmission over copper. Because of this, the maximum length for an ACC is typically 2 to 3 meters farther than the corresponding DAC.

ACCs provide an option when passive copper does not provide enough reach, but the deployment does not require an optical connection.

AECs

Active Electrical Cables, or AECs, are another variant of DAC. An AEC includes a driver to amplify the signal and also features forward error correction, or FEC, and retimer functionality to provide balanced signals for low bit error rates.

This makes AECs useful in high-speed 400G and 800G environments where signal integrity and reach requirements exceed passive copper capabilities but the deployment does not require an optical link.

Consideration 1: Transmission Distance

The distance supported by each cable type is governed by the transmission medium. AOCs generally have the greatest reach. Copper-based cables are more affected by internal crosstalk and external EMI, which limit maximum supported length. ACC and AEC designs compensate for some of these limitations.

While AOC supports distances that include the typical DAC, ACC, and AEC ranges, other factors often steer selection toward one of the copper or active electrical technologies. Those factors include power consumption, cost, cable density, and the surrounding rack design.

Axiom Engineering typically starts interconnect selection with the actual physical link requirement. A 400G or 800G connection inside a rack presents a different set of requirements than the same data rate running between racks or rows.

Consideration 2: Power Consumption

DAC has the shortest reach but also the lowest power consumption. AOCs support the greatest reach but have higher power consumption because they include optical components and chipsets for signal conversion and retiming.

Lower data rate cabled transceivers were traditionally available primarily as DACs or AOCs. There were active DACs, but those experienced interoperability issues because the host device had to provide functionality that was not always available to support longer lengths.

The development of ACCs and AECs expanded the available design options. ACCs consume slightly more power than DACs. An 800G ACC may require approximately 1.5W per end due to the additional signal-processing chipsets built into the device. AECs address the need for greater reach without the optical engine power requirement. As a result, AECs can run 25 to 50 percent lower power than equivalent AOCs.

Power consumption is an operational consideration for both electrical capacity and cooling because much of the consumed power contributes to thermal load. Axiom's engineering approach considers power and thermal impact as part of the interconnect decision, especially in high-density 400G and 800G environments.

Consideration 3: Cost

Because optical fibers are generally more expensive than copper cables, the price of an AOC is typically higher than a DAC at a similar data rate and form factor. The cost of an AEC falls between DAC and AOC and is higher than an ACC.

ACC costs more than passive DAC because of the active chips inside. AEC is usually slightly more expensive than the corresponding ACC because of its added signal integrity and retiming features.

In Axiom's interconnect selection process, these cost differences are evaluated alongside reach, signal integrity, power, and host-platform requirements. Choosing solely on cable price can create problems if the selected interconnect does not meet the requirements of the physical link or host environment.

Applications

Across Axiom's 400G and 800G interconnect planning, the cable type is matched to the individual link rather than applying one technology across the entire network. Rack layout, port speed, host platform, link distance, power budget, thermal conditions, and interoperability requirements all influence the final selection.

Conclusion

There are several technologies available for connections within a data center. DACs offer the lowest cost and power consumption but the shortest reach. AOCs support the longest reach but require more power and carry a higher cost. ACCs and AECs fill important positions between those two options where balancing reach, signal integrity, power consumption, and cost is critical.

Axiom's approach to high-speed interconnect selection is to evaluate reach, signal integrity, power, thermals, host compatibility, and cost together. At 400G and 800G, the right choice depends on the specific link and deployment environment rather than choosing one cable technology as the default across the network.

For engineering teams planning high-speed infrastructure, the goal is to select the right technology for each link and validate the choice under the conditions the network will experience in production.

DAC, AOC, AEC, and ACC FAQs