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How to use DAC Cables

Fiber optic networking runs the world, but designing and maintaining a network is not a simple task. You’ll have to compare a lot of different equipment choices, and considering the power and equipment demands, it can be easy to go over your budget.

Finding ways to save money without sacrificing performance is essential, and one tool that can help you with this is the DAC cable.

What Are DAC Cables?

Direct attach copper (DAC) cables are designed to work with fiber optic networks. The copper cables typically run around 26 to 28 AWG, and they allow for communication between devices along the copper wires.

DAC cables are designed specifically to integrate with fiber optics systems, meaning you can find DAC cables with a number of standard fiber connections (like QSFP+). This allows the DAC cables to plug and play with the fiber optic hardware, allowing for an additional connection type.

Naturally, copper connections tend to run much slower than fiber connections, and copper cannot cover the same distances. But, when a fiber network has devices or nodes that are close enough together, DAC cables are fast enough to keep up with many fiber applications.

Typically, the effective operating range for DAC cables is going to be in the ballpark of seven meters, so devices need to be relatively close. That said, when DAC cables are applicable, they represent an opportunity for cost savings. DAC cables typically cost far less than their fiber counterparts, and integrating them into a fiber network can save thousands of dollars.

How Are They Used?

If DAC sounds promising for your network, then you might be wondering how you can use them.

In general, you can connect fiber optic nodes that are within the range limitations of DAC cables. For instance, you can connect switches in the same stack to each other using DAC. Each DAC cable in the stack represents money saved by cutting more expensive fiber options.

Still, to properly use DAC, you need to know a little bit more about how the technology works and what some of your choices are. For instance, there are passive and active DAC cables, and they come with different pros and cons. You also want to compare DAC options to optical transceiver modules.

You’ll find a breakdown of both concepts below.

Passive vs Active

There are passive and active DAC cables, and they suit different purposes.

Passive cables are exactly what they sound like. The cables do not utilize external power sources. Instead, they sit passively, and signals can run through them. Because of this, they have very low power consumption. As long as the signal has enough force to get through copper resistances (which will typically consume less than 0.15W), the passive cable works just fine.

But, the passive cable has a short range. They usually max out at around seven meters. Any run longer than that, and the passive cable can inhibit network performance.

Meanwhile, active cables have electrical components that are used to boost the signal. This signal boost requires additional power, but it extends the range to 100 meters (at 40G speeds) and even further for slower speeds. Active cables are more expensive, and they come with additional power costs.

This makes the choice between the two DAC types pretty easy. If passive cables get the job done, they’re cheaper and an obvious option. If you need active DAC, it’s still going to be cheaper than the majority of fiber choices.

DAC and Optical Transceiver Modules

The best way to understand how to apply DAC cables is to compare them to optical transceiver modules. Transceiver modules allow you to connect a number of devices to your fiber optic switch using fiber optic lines. When connecting switches in a stack together, transceiver modules and DAC cables can perform the same function.

Since switch stacks usually keep components relatively close together, intrastack connections are great candidates for DAC cables. In this case, the DAC cables consume far less power and cost a lot less up front.

That is, the best way to use DAC cables is to replace optical transceiver modules when connecting switches in the same stack together.

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