DAC: Direct Attach Cable

Acronym Series

Written by: Scott Hammond, Senior Security Engineer
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In our Acronym Series, Nexum’s expert engineers define the industry’s most popular topics.

Acronym: DAC – Direct Attach Cable

Definition: DACs are a low-cost, high-speed connection option for short distances meant to replace optical modules.


For all our love of wireless, we still must physically plumb hardware devices for connectivity to a network. Traditionally that is done via fiber for long distances and copper for shorter requirements. Optical transceivers tend to be expensive, but copper is much more cost-effective. DACs comprise a copper twinaxial wire of varying lengths that terminates at a modular transceiver on each end.

It was only recently that 10GBase-T ports became commonplace. DACs have helped leverage modular ports for speeds up to 40G/100G /400G (and likely will be beyond that in the not-too-distant future).

There are two available types: Passive DACs and Active DACs. Passive DACs support lengths of .5 to 5 meters, while Active DACs support 5-10 meters. If you need something beyond that, it’s time to buy some optics. Active optical cables (AOCs) are similar to DACs in that they are prefabricated to length and share the cost advantage over traditional optical modules.

The modules used in DACs are known as small form-factor pluggable (SFP) and quad small form-factor pluggable (QSFP).

We see DACs in use wherever you find physical hardware requiring a high-speed connection. High Availability between devices would be a prime example of where one might expect to find a DAC in play.


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