DAC vs AOC vs AEC vs ACC: Choosing the Right High-Speed Interconnect for 400G/800G Networks

A closer look at their roles in the network infrastructure

Jul 29, 2025

In today’s modern data center, there are many acronyms for devices and connections.  Even if we narrow our focus to the connections between switches, routers, GPUs and servers, we are left with several terms that need definition.  The topic of this article is the family of cables for connecting optical ports on devices.

There are many options for cabled transceivers – fixed length connections with a transceiver ‘form factor’ as their connection point:

• DACs

• AOCs

• AECs

• ACCs

The following article is an overview of these technologies, and a guide on how to choose the correct type of cabled solution based on system and design requirements.

DACs

Direct Attached Cables (DACs) are cables with transceivers as their connectors or end points.  While they are the same form factors as optical transceivers, their transmission medium is copper. These cables are passive, meaning they do not include any active components like a typical transceiver.

These cables are offered in various data rates, and different form factors – from 10G SFP+ through to 800G OSFP form factors.

In addition to point-to-point cable configurations, DACs are also available as breakout cables.  These breakout cables split a higher data rate connection (40G and beyond) into lower data rate lanes.  For example, a 40G to 4 x 10G breakout, or a 100G to 4 x 25G version. These breakout configurations are very helpful for connections to a Top-of-Rack (ToR) switch from multiple servers or network interface cards.

Because of the usage of copper as the transmission medium, the maximum length that a DAC can support will vary depending on the data rate, because of interference/crosstalk issues with such high transmission speeds.  For data rates greater than 400G, a DAC will have a maximum length of around 3 meters.

AOCs

Active Optical Cables (AOCs) are the most like a ‘standard’ fiber optic connection.  They utilize optical fiber as the transmission medium, they convert electrical signals into optical signals, just like a standard transceiver.  However, unlike a standard pluggable transceiver, the fiber cable is permanently attached.  They are less expensive than a pair of fiber optic transceivers because the optical components are coupled to the fiber cabling, and this is a processing benefit that can reduce the costs.

AOCs – like DACs – are also available in a multitude of data rates and form factors.  They are also available as breakout cables.

Active Optical Cables, due to having similar designs of a standard optical transceiver, are able to support lengths of ~100m, though are not typically used for such lengths (the routing of a cable with a transceiver housing attached at one end is prohibitive in many deployments.

ACCs

Active Copper Cables (ACCs) are a variation of traditional DACs. Like a DAC, an ACC uses copper cabling as its transmission medium. Unlike a DAC, an ACC has an active signal driver or equalizer inside. These chips compensate for losses caused by transmission over copper. Because of this, the maximum length for an ACC is 2 to 3 meters farther than the corresponding DAC.

AECs

Active Electrical Cables (AECs) are another variant of a DAC (like an ACC).  However, an AEC not only includes a driver to amplify the signal, but they also feature forward error correction (FEC) and retimer functionality to provide balanced signals for very low bit error rates.  

Consideration 1: Transmission distance

The distance that can be supported by these various cable types is governed by the transmission medium.  Therefore, AOCs will always have the greatest reach.  Both internal crosstalk and external EMI are detrimental to the overall length that a copper-based cable can reach.  The ACC and AEC varieties can compensate for this, but only so much.  

While an AOC can support short distances, and encompasses the lengths that DACs, ACCs and AECs support, other factors will typically steer selection to one of these technologies.  Those are power consumption and cost.

Consideration 2:  Power Consumption

The DAC solution is the shortest reach solution, but it is also the lower power consumption. AOCs as mentioned, can support the greatest reach, but they have the highest power consumption, as they feature optical components, as well as chipsets for signal conversion and retiming occurring onboard.

Lower data rate cabled transceivers were only available in DAC or AOCs. There were ‘active’ DACs but these had interoperability issues, as the host device had to provide functionality that was not always available to support longer lengths. This changed with the development of ACCs, and AECs. ACCs are slightly more power-hungry than DACS (an 800G ACC will require 1.5W per end) and as mentioned in the earlier section, this is due to the additional signal processing chipsets built into the device.  However, there is still the need for the AEC, for greater reach without the optical engine ‘power tax’.  As a result, AECs can run 25-50% lower power than the equivalent AOCs.

Power consumption is an operational consideration, not only for powering of a data center, but also in terms of the cooling requirements, as much of that power goes to thermal energy.

Consideration 3:  Cost

Due to the generally higher cost of optical fibers compared to copper cables, the price of AOC is typically higher than that of DAC (assuming similar data rate/form factor). The cost of AEC falls between DAC and AOC, and higher than an ACC.  The cost of ACC is higher than that of passive DAC due to the presence of active chips internally, and the AEC is slightly more than the ACC equivalent.

Applications

• DAC are primarily used within system racks, connecting compute servers to storage subsystems within a maximum length of 3 meters.

• AOCs can be used in any applications that a DAC, ACC, or AEC, but because they can support longer reaches (at a higher cost) they are typically reserved for the longer links – between racks and even rows in a data center. 

• ACCs, supporting longer lengths than a passive DAC are used in data centers and high-performance computing for linking network devices, servers, and storage equipment

• AEC provides a longer transmission distance compared to DAC or ACC, so they are suited for intra-rack and inter-rack scenarios – usually neighboring racks in a row.

Conclusion

There are a variety of technologies for connections in a data center.  DACs offer lowest cost and power consumption, but the shortest reach.  AOCs can support the longest reach, but will require the most power, and are the highest cost.  Because of this, ACCs and AECs are very helpful for portions of a network where the balance of reach, power consumption, and cost can be critical.