DAC, ACC, or AEC?

Steffen Dammel 28. Aug 2026

The Guide to Choosing the Right Copper Connection for Your Rack

Servers, switches, and routers all need to be connected, but not every connection needs fiber. For short to medium distances within or between neighboring racks, direct-attach copper is often the smarter choice: cheaper, more power-efficient, and lower-latency than optical solutions. But "copper cable" isn't just one thing: DAC, ACC, and AEC are three different technologies hiding behind similar-looking connectors, and picking the right one comes down to reach, power draw, and operational reliability.

The shared principle

All three are what's known as direct-attach cables: a continuous twinax copper cable permanently attached to the connectors on both ends (SFP, QSFP, OSFP, and so on), with no separate transceiver and no pluggable fiber patch. That holds true whether or not there's active electronics inside the connector. "Direct attach" simply describes the fixed cable-to-connector assembly, not what happens to the signal along the way. The real difference between DAC, ACC, and AEC comes down to how much electronics sits inside the connectors and what that electronics does to the signal.

DAC – Direct Attach Cable (passive)

The simplest and cheapest option: pure twinax copper with no active signal processing at all. The signal travels from sender to receiver unchanged.

Signal processing: none (fully passive)
Reach: heavily dependent on data rate and cable gauge (AWG), up to 5 m at 25G/100G depending on gauge, typically only 1–2 m at 800G
Power draw: very low, since it's a purely passive cable with no active components
Latency: no added processing latency, since there's no redriver or retimer in the signal path; just the raw propagation delay through the cable
Cost: the most affordable option
Breakout: also available as a breakout cable, e.g. 400G to 4× 100G

As data rates climb, copper's signal loss quickly becomes the limiting factor. That's why passive DACs get shorter, thicker, and stiffer at higher data rates.

Best for: the shortest links in the rack, e.g. top-of-rack switch to server.

ACC – Active Copper Cable

ACC adds a small piece of active electronics inside the connectors: a redriver/equalizer. It boosts the electrical signal and compensates for copper loss: it "refreshes" the signal rather than regenerating it from scratch.

Signal processing: analog conditioning (redriver/equalizer), no retiming
Reach: longer than passive DAC, typically up to about 5 m at high data rates
Power draw: low, usually in the low single-digit watt range
Cable design: thinner and more flexible than a passive DAC at the same reach
Breakout: also available as a breakout cable, e.g. 800G to 2× 400G

Worth noting: a redriver doesn't generate a new clock signal. It compensates for cable-induced distortion (inter-symbol interference), but it also amplifies incoming noise and jitter along with the signal, rather than resetting the jitter budget. That makes ACC the middle ground between DAC and AEC.

Best for: a bit more reach or a more manageable cable, without the full complexity of a retimer.

AEC – Active Electrical Cable

The most sophisticated copper option: instead of a redriver, AEC uses a DSP-based retimer inside the connectors. It fully recovers clock and data (Clock Data Recovery) and transmits a completely regenerated signal.

Signal processing: full retiming with CDR
Reach: the longest of the copper options, up to 7 m. The maximum depends on the form factor combination: longest when both sides use the same form factor (e.g. OSFP↔OSFP), somewhat shorter in breakout configurations that mix form factors (e.g. OSFP↔QSFP-DD)
Power draw: noticeably higher than DAC/ACC, since the DSP retimer is actively processing the signal rather than just boosting it. At 800G, that's roughly 10–13 W per cable end depending on form factor, or about 21–26 W for the full cable. At 400G it's markedly lower, around 4 W per end (~8 W total)
Flexibility: available as a breakout cable too, just like DAC and ACC (e.g. 800G to 2× 400G). Breakout isn't an AEC exclusive; it's common across all copper and AOC variants

Because the retimer rebuilds the signal from scratch, AECs can be made thinner and more flexible than a passive copper cable of the same reach, a real advantage in densely packed, modern racks.

Best for: 400G/800G links within the rack or between neighboring racks, when DAC's reach falls short but a full optical solution would be overkill.

DAC,ACC & AEC Compared

Three twinax copper solutions for short data center links - from fully passive to fully active with signal conditioning. Power draw and cost increase from left to right - reach holds up to 5m for DAC and ACC, then extends 7m with AEC.

Direct Attach Cable

DAC

Fully passive twinax copper, with no active electronics at all. The signal passes through electrically unchanged.

Reach≤ 5 m*
Power drawMinimal
Chip technologyNone
LatencyLowest
Cost$

Pros, cons & typical use

Lowest cost, virtually no power draw
Minimal heat, very robust
Lowest latency of the three

Reach drops sharply at higher data rates
Thicker and less flexible to route

Typical use: server ↔ top-of-rack switch, short in-rack links.

Active Copper Cable

ACC

A redriver chip at each end analog-boosts and reshapes the signal to offset cable loss, without full retiming.

Reach≤ 5 m
Power drawVery low
Chip technologyRedriver (1x)
LatencyVery low
Cost$$

Pros, cons & typical use

Better signal integrity than DAC
Thinner & more flexible to route
Still power-efficient vs. AEC/AOC

Needs power, unlike passive DAC
Lower signal quality than AEC

Typical use: medium-distance links, e.g. chassis ↔ rack switch.

Active Electrical Cable

AEC

A DSP-based retimer at each end fully recovers clock & data and re-transmits a clean, regenerated signal.

Reach≤ 7 m*
Power drawLow
Chip technologyRetimer + CDR (2x)
LatencyLow
Cost$$$

Pros, cons & typical use

Best signal quality of the copper trio
Longest reach of the three, up to 7 m
Cheaper & more efficient than AOC

Highest power draw & cost of the copper trio
More complex electronics, more failure points

Typical use: high-density/AI clusters, multi-hop links within a rack cluster.

In short

The more active the cable, the farther it reaches and the better the signal, at the cost of power, price, and complexity.

Choose DAC

For short, low-cost in-rack links with no compromise on latency or power draw.

Choose ACC

As an efficient middle ground: better signal integrity than DAC, at a moderate step up in cost and power.

Choose AEC

When maximum copper reach and signal integrity matter, before AOC becomes necessary.

* Reach depends on data rate and cable gauge (AWG): typically up to 5 m at 25G/100G, around 1–2 m at 800G for DAC. AEC's 7 m maximum applies when both ends use the same form factor - breakout configurations that mix form factors reach somewhat less. Power draw and cost are shown relative to each other - exact values vary by data rate and form factor.

And what about fiber?

When none of these copper options can bridge the distance, fiber comes into play in two forms: AOC (Active Optical Cable), which is permanently attached to its connectors just like DAC/ACC/AEC (and also available as a breakout cable, e.g. 800G to 2× 400G), except it transmits optically instead of electrically; or a classic pluggable transceiver with a separate fiber patch cable, which reaches much further still, from a few hundred meters up to tens of kilometers depending on the transceiver type. AOC typically reaches up to 30 m, sometimes up to 100 m, at a noticeably higher power draw than copper, especially at high data rates. AEC already draws a meaningful amount of power at 800G too (around 21–26 W for the full cable). AOC tends to run a bit higher still at comparable data rates (roughly 24–34 W), so copper's efficiency edge over fiber narrows at the highest data rates, though it doesn't disappear. For short links within and between racks, DAC, ACC, and AEC remain the more efficient and cost-effective choice in most cases.

Roughly speaking, in the data center: the shortest server-to-ToR (top-of-rack) links typically run on DAC, while longer or inter-rack links (ToR-to-spine) are more likely to use AOC, AEC, or ACC.

Making the right call

Shortest distance, maximum efficiency, minimal latency? → DAC
A bit more reach or a more manageable cable? → ACC
Highest speeds (400G/800G) with maximum reach and signal quality? → AEC (though at 800G, that comes with noticeably higher power draw)

Knowing these three technologies, and their trade-offs, means you can cable your rack more reliably, more cost-effectively, and more efficiently. Have questions about the right solution for your setup? Get in touch, we're happy to advise.

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