Passive vs Active DAC cable: How to Choose?

Passive vs Active DAC cables: how do you select the appropriate type when buying a DAC cable? This blog will provide the necessary insights.

What is a DAC cable?
Passive vs Active DAC cables: What is the difference?
Optcore’s Passive and Active DAC cable
FAQs
Conclusion

What is a DAC cable?

DAC, which stands for Direct Attach Copper cable, is a type of copper twinax cable with different fixed connectors at both ends. DAC cables can be divided into two main categories: Passive DAC cable and Active DAC cable. Depending on the connector type, these DAC cables are called 10G SFP+ DAC, 40G QSFP DAC, 100G QSFP28 DAC, 200G QSFP56 DAC, and 400G QSFP-DD DAC.

These cables are commonly used to connect switches, routers, servers, and other storage devices within a data center or between adjacent racks. DAC cables are more cost-effective for short-distance applications than optical transceivers and AOC cables (Direct Attach Optical Cable).

Passive vs Active DAC cables: What is the difference?

#1 Main difference

It’s hard to see the difference between these two threads from the outside. The essential difference between active and passive DACs lies in signal conditioning. Active DACs use electronics for signal conditioning, while passive DACs do not.

#2 Cable length difference

Passive DAC does not contain electronic components, so its transmission distance is relatively short. AWG24 copper wire can only transmit up to 7 meters. Suppliers also produce 10 meters of passive DAC, but it is recommended not to use such a long passive cable; the signal transmission is poor.

The signal quality is better because electronic devices are used for signal conditioning. The longest transmission distance for the AWG24 Active DAC cable is 15 meters.

#3 For different types of devices

For proper signal processing, it’s essential to ensure compatibility between the type of DAC used and the networking equipment. Most equipped switches support Passive DACs.

The remaining some perform no signal conditioning and must be fitted with substantially more expensive Active DACs if copper interconnection is desired. However, since these switches do not contain the signal conditioning on each SFP+ port, they are considerably cheaper.

So, when you choose a DAC cable for your device, it is essential to check which kind it supports.

#4 Cost difference

Length, cost, and performance requirements are important considerations when choosing between passive and active DACs. Passive DACs are suitable for short connection distances and are a more affordable and cost-effective solution for projects with limited budgets. Active DACs, on the other hand, are more expensive, especially for high-bandwidth and data-intensive applications that require higher performance and reliability.

If you are on a budget and want to save money, you may consider purchasing a third-party compatibility DAC. Optcore’s compatible Active and passive DACs are more cost-effective than branded products and are compatible with multiple brands, such as Cisco, Arista, Juniper, Extreme, and more.

Optcore’s Passive and Active DAC cable

FAQs

Q1: Can I use Active DAC for cable length within 7m?

A1: Yes, of course. If you require a higher level of transmission performance, or if your switch can only support Active DAC, then you can also choose short-range Active DAC, such as Brocade XBR-TWX-0301 and Juniper QFX-SFP-DAC-3MA, which are short Active DACs.

Q2: If my transmission distance exceeds 15M, which cable should I choose?

A2: In the actual application of 1-7M distance is recommended to use Passive DAC, 7-15M is recommended to use Active DAC, 15-100M is recommended to use AOC active optical cable, 100M or more is recommended to use optical modules and optical cable connection.

Q3: Can the 40G port and 10G port be connected using DAC?

A3: Yes, 40G DACs are available as QSFP+ to 4*SFP+Breakout cables, which are suitable for interconnecting 40G and 10G devices with a 40G interface at one end and four 10G interfaces at the other end.

Q4: Can I use 10G SFP+ DAC cable to SFP port of switch?

A4: Yes, you can plug the SFP+ DAC cable into SFP ports. However, the SFP cable can’t be used in SFP+ ports. It can be plugged into SFP+ ports, but that won’t work. When you use the 10G SFP+DAC cable, please turn auto-negotiation off for both devices for linked ports.

Q5: Can I use one DAC cable to connect two different brands of switches?

A5: If you purchased DAC cables from one brand supplier, such as Cisco SFP-H10GB-CU1M, they can only be used with Cisco brand devices and can’t connect to other special brand devices(such as Arista, Juniper, Extreme), which need special codes. Some devices that don’t require special compatibility codes don’t matter. Optcore can provide Customized DACs with different compatibility on both connectors if you need one DAC cable to connect two special devices.

Conclusion

The decision to use passive or active DAC cables depends on factors such as cost, distance, performance, and the requirements of different devices. Passive DACs are affordable and appropriate for short distances but have poor signal integrity over long distances. In contrast, active DACs provide better performance over longer distances and are suitable for high-bandwidth applications despite being more expensive.

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