DAC (Direct Attach Cable) looks like AOC in appearance. It is also a wire with two modules tied at each end, but the middle wire is copper Cable instead of optical fiber.

AOC is called active cable, while DAC is divided into active and passive, and the mainstream is passive. Some manufacturers in order to let the DAC can be transmitted farther, which adds a signal amplification chip, this is the active copper cable.

Strictly speaking, DAC is not a category of optical modules; it just looks like optical modules on the outside, but inside, it has nothing to do with optical modules. There are no lasers, no amplifiers, no detectors, and no MCU controller as complex as the optical module. In other words, the most expensive key component in the optical module /AOC, the DAC, does not have a simple control chip for electrical signals, which are transmitted from beginning to end. This is why the price of DAC is much lower than optical modules and AOC.

We know that when the optical module or AOC is plugged into the switch interface, the voltage, current, temperature, receiving and transmitting optical power of the optical module of the interface can be seen by using the command on the switch. But if plugging a DAC doesn‘t usually read this information, why is that? The reason is that both the optical module and the AOC have a DDM store that stores this information. In DAC, on the one hand, there is no concept of receiving and transmitting optical power; on the other hand, there is no MCU chip with strong function to detect temperature, voltage and current. Therefore, DAC usually does not have DDM information. When you see that the DAC can‘t read this information, don‘t doubt the switch, don‘t doubt the DAC, this is a common practice in the industry.

Because DAC is purely electric drive, so the distance is generally not far, because the electrical signal than the optical signal is more likely to be limited by the distance (poor anti-interference ability), generally within 5M, unless the active cable, plus an amplifier. Compared with light, electrical signals are more likely to be interfered by distance, temperature, radiation, cable folding and other issues, so DAC is more prone to compatibility issues than AOC, depending on the driving capability of the devices at both ends. For AOC, the main problem is that fiber breaks easily, and of course, a lot of light today is pretty foldable.

So in general, if the environment is controllable, the distance is not long, the price is sensitive, and the compatibility problems can be eliminated in advance, the DAC is a good choice.