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What is direct attach cable used for?
Knowledge Base + 2023.12.08

Direct attach cables (DAC) are used for high-speed, short-distance data transmission in network and storage applications. They are commonly used to connect switches, routers, and servers within a data center or enterprise network. These cables offer a cost-effective and power-efficient solution for connecting networking devices and can support data rates of up to 400 Gbps.

What’s the difference between Active DAC and Passive DAC cables?

The main difference between Active DAC and Passive DAC is that Active DAC makes use of electronics for signal conditioning, while Passive DAC does not make use of electronics for signal conditioning.

Passive DAC is used when signal conditioning integrated into a port is provided by a switch. It costs less than Active DAC, but has a higher upfront cost.

Active DAC is used when a signal conditioning integrated into a port is not provided by a switch. Active DAC generally costs more than Passive DAC, but the switch that comes with Active DAC costs less.

Over 80 percent of SFP+ equipped switches that are available for sale support Passive DACs. The rest of the 20% work on no signal conditioning and hence are only compatible with the costly Active DACs along with copper interconnection. The switches that don’t have signal conditioning on each SFP+ port cost much less.

Which Switch is Better for You – One That Supports Active DAC or Passive DAC?

Whether you choose a switch that supports Passive DACs or Active DACs will depend on two factors…

Fiber Connectivity – If the application for which the switch is required makes use of SFP+ transceivers only, then you may not need the switch to support Passive DACs. However, if the

SFP+ ports are compatible with the DACs, then you are going to save more over the long-term with low-cost Passive DACs compared to the more expensive Active DACs, although the switches may be priced higher.

Length of DAC Spans – What is the primary application for which the DACs are used? If it is limited to within racks or between adjacent racks, which means a short distance of 7 meters or less, then you are better off using switches that support Passive DACs. However, if the DACs are more than 7 meters in length, then Active DACs would make for a better choice. In case the switch supports signal conditioning identifies an Active DAC, then it will not make use of its internal signal conditioning circuitry. That application is left to the Active DAC.