What is DAC Cable? The Definitive Guide

DAC cable is a direct attach copper cable that contains two specific connectors on both ends. This cable allows direct communication between networking devices over copper wire.

As a networking engineer, I want to share my knowledge and help you understand the basics. In this guide, I compiled all the information regarding DAC cables.

Table of Contents

• What is DAC cable
• What is DAC breakout cable
• Differences between DAC cable and Fiber
• Types of DAC cables
• FAQ
• Conclusion

Keep reading to learn more.

What is a DAC cable?

A DAC cable is short for direct attach cable. It is a pre-terminated twinax copper cable assembly with two pluggable connectors, thereby allowing connecting the ports directly within active platforms, such as networking switches, routers, servers, adapter cards, or data storage devices.

Take the SFP+ DAC cable as an example, shown in the below picture; it consists of a fixed length (usually less than 7 meters) Twinax cable and two SFP+ transceivers. The four-pair copper cables were soldered with a circuit board of SFP+ transceivers, finally achieving a max bidirectional 10G high-speed rate.

What is a DAC Breakout Cable?

Sometimes we classify breakout cable as another DAC cable. The DAC breakout cable consists of one connector on one end but multiple (2 or 4) connectors on the other.

In simple words, it splits one connector into multiple connectors. The one connector side provides a much higher speed (such as 40G), while the “split” ends at a lower speed (10G). Therefore, the breakout cable is useful for connecting different speed ports.

In some circumvents, the breakout DAC act as an adapter to upgrade the low speeds ports to higher-speed ports and increase faceplate port density.

DAC Cable vs. Fiber

Fiber is a critical component of modern networks. Combined with fiber transceivers, they deliver a cost-effective ultra-high bandwidth networking transmission solution.

Unlike fiber cable and transceiver, direct attach cable has its advantages and shortages. Now let us make a simple comparison. It will help you make the right decision.

Based on the table’s comparison, you should clearly understand their difference and advantages.

DAC is the better choice for very short-distance connectivity (Typically short than 10 meters) in data centers and storage applications if you have a limited budget and do not care about the cabling space.

But for longer-distance connectivity, fiber cabling will provide better performance and space-saving.

Consider it for the future and calculate the total cost if possible.

How to classify DAC cables?

Based on the different benchmarks, we can divide them into different types.

According to the availability of signal conditioning functions, we can divide them into passive and active DAC.

Passive DAC Cable

Passive DAC does not contain electronics for signal conditioning and amplification. Therefore it provides a lower price but a limited length (typically 7m for 10G). The passive cable will generate many bit errors for long distances.

Active DAC Cable

Active DAC contains a microprocessor and other electronics for signal conditioning and amplification, which provides better performance for longer-distance transmission.

Because of its additional electronics, the price is higher than passive cable and more expensive than AOC cable. Before you purchase an active cable, comparing the total cost with AOC or fiber transceiver will be better. You may find a better cost-saving solution.

Classified by Data Rate and Form Factor

• SFP Cable: SFP to SFP, offers 1G speed for gigabit ethernet SFP port connectivity
• SFP+ Cable: 10G SFP+ to 10G SFP+, suitable for SFP+ port connectivity. This type is the most popular copper cable with a relatively low price, widely used in data centers and enterprise networks.
• SFP28 Cable: 25G SFP28 to 25G SFP28, support typically 25G speed for SFP28 port, usually used in 25GbE Ethernet application.
• QSFP+ Cable: 40G QSFP+ to 40G QSFP+, suitable for 40G QSFP+ port.
• 56G FDR Cable:56G QSFP+ to 56G QSFP+, provides 56G (4x14G) speed, suitable for InfiniBand in the enterprise data center.
• QSFP28 Cable:100G QSFP28 to 100G QSFP28, provides 100G (4x25G) speed, suitable fo
• QSFP56 Cable:200G QSFP56 to QSFP56, , support 200G (4x50G) speed.
• 400G QSFP-DD Cable: 400G QSFP-DD to 400G QSFP-DD, support 400G (8x50G) speed.
• 800G QSFP-DD Cable: 800G QSFP-DD to 800G QSFP-DD, support 800G (8x100G) speed.
• 40G Breakout Cable: 40G QSFP+ to 4x 10G SFP+
• 100G Breakout Cable: 100G QSFP28 to 4x 25G SFP28
• 200G Breakout Cable: 200G QSFP-DD to 2x 100G QSFP28, 200G QSFP56 to 4x 50G SFP56
• 400G Breakout Cable: 400G QSFP-DD to 4x100G QSFP56, 400G QSFP-DD to 2x200G QSFP56

FAQ

Q: Can you provide a compatible DAC cable for cross-brand linking?

A: Sure, we can. We provide customized direct attach cables with different compatibility on a cross-brand switch, allowing for a perfect link.

Q: What is the maximum length of a DAC cable?

A: It depends on their data rate.

• A passive 10G DAC cable can offer a maximum length of 10 meters (~33 feet), while an active 10G cable can reach 15 meters (~49 feet).
• 40G DAC cable can offer a maximum length of 7 meters (~23 feet).
• 100G DAC cable can offer a maximum length of 5 meters (~16 feet).
• 400G DAC cable can offer a maximum length of 3 meters (~10 feet).

You may consider the AOC cable or optical transceiver for long-distance applications.

Final Words

Now I hope you enjoyed my guide to DAC cables.

Are you clear about their meaning and types?

What types of DACs are used in your switches?

Do you plan to upgrade to 100G or 400G DAC?

Are there any topics missed in this post?

Let me know by Leaving a message now.

Read more:

• What is the difference between DAC and AOC Cables?
• What you need to know about Optcore 400G QSFP-DD DAC Cables
• 10GBASE-T Cabling vs. 10G SFP+ DAC, Which One is Better?