In short: for connections inside a rack, a direct attach cable (DAC) is the cheapest and simplest option. For a few meters more, or where a thinner, lighter cable helps, an active optical cable (AOC) is the next step. For anything longer – or when you want to change the cable without changing the modules – use two optical transceivers and a separate fiber patch cable.
All three connect the same SFP+ ports. The difference is in distance, cost and handling.
Three ways to connect two ports
| DAC | AOC | Transceivers + fiber | |
|---|---|---|---|
| What it is | copper cable, modules fixed on both ends | fiber cable, modules fixed on both ends | two separate modules and a patch cable |
| Typical length | 0.5–7 m passive, up to 10 m active | 1–30 m | from a few meters to 80 km |
| Cost | lowest | medium | highest per link |
| Cable | thicker, stiffer | thin and light | any standard fiber |
| Best for | inside a rack | between neighbouring racks | across a room, a building or further |
DAC – direct attach copper
A DAC is a copper twinax cable with an SFP+ module permanently attached to each end. There is no laser and no optics, which makes it the most affordable and the most energy-efficient way to connect a server to a top-of-rack switch, or two switches stacked in the same rack.
- Passive DAC cables are the standard for short runs – our range goes from 0.5 m to 7 m.
- Active DAC cables contain a small signal amplifier, which makes longer lengths possible – up to 10 m in our range.
The downside is the cable itself: copper twinax is thicker and less flexible than fiber, which matters in densely packed racks.
AOC – active optical cable
An AOC looks like a DAC but uses fiber between the two ends, with the optics built into the modules. The cable is thin, light and easy to route, and it reaches further than copper – our range goes up to 30 m. AOCs are a good fit between neighbouring racks or across a row, where a DAC would be too short or too bulky.
10G active optical cables from 1 to 30 mThin, light fiber cable with the modules built in.
Optical transceivers and a patch cable
Two separate transceivers and a fiber patch cable are the most flexible solution. The fiber can be any length and can run through patch panels and walls; if the cable gets damaged you replace the cable, not the modules; and you can choose the reach you need – from SR for a few hundred meters to ZR for 80 km. The types are explained in 10G SFP+ types: SR, LR, ER, ZR.
How to choose
- Both devices in the same rack? A passive DAC.
- Neighbouring racks, or the DAC would be too stiff? An AOC or an active DAC.
- Across a room, through patch panels or further? Transceivers and fiber.
- Coding: like any module, the ends of a DAC or AOC have to be accepted by the devices they plug into. If the two devices are from different brands, let us know when you ask for a quote.
Frequently asked questions
Is a DAC faster than a fiber link?
Both carry 10 Gbit/s. A DAC has no optical conversion, so it uses less power and adds a little less delay, which is why it is popular inside racks.
What is the difference between a passive and an active DAC?
A passive DAC is just copper between the two modules; an active DAC has electronics that strengthen the signal, so it can be longer.
When should I use an AOC instead of a DAC?
When the run is longer than a DAC allows, or when a thinner, lighter cable makes routing easier.
