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What you need to know about 400G QSFP-DD DAC Cables?
Knowledge Base + 2024.01.10

A 400G QSFP-DD (Quad Small Form-factor Pluggable Double Density) DAC (Direct Attach Copper) cable is a high-speed interconnect cable commonly used in data centers for short-distance, high-bandwidth connections. Here are some details about the 400G QSFP-DD DAC cable:

Form Factor: QSFP-DD is an evolution of the QSFP form factor, with double the number of lanes. It allows for higher data rates and increased bandwidth.

Data Rate: The cable supports data rates of up to 400 Gbps, making it suitable for high-performance networking applications.

Connector Type: The QSFP-DD DAC cable has QSFP-DD connectors on both ends. These connectors are designed to accommodate the increased number of lanes for higher data transfer.

Cable Type: DAC cables are copper-based, providing a cost-effective and power-efficient alternative to optical transceivers. They are ideal for short-distance connections within a data center.

Length Options: QSFP-DD DAC cables are available in various lengths to accommodate different networking needs. Common lengths include 1m, 3m, 5m, and more.

Compatibility: QSFP-DD DAC cables are designed to be compatible with networking equipment that supports QSFP-DD interfaces. It's essential to ensure that the cable is compatible with the specific devices you are connecting.

Applications: These cables are commonly used for high-speed interconnections in data centers, connecting switches, routers, and other networking devices.

Cost-Effective: DAC cables are often more cost-effective than optical transceivers and fiber optic cables, especially for short-distance connections.

Hot-Pluggable: Like other QSFP cables, QSFP-DD DAC cables are hot-pluggable, allowing for easy and convenient installation and removal without disrupting the entire system.


Features and Specification

The 400G DAC cable can be divided into 400G QSFP-DD to QSFP-DD DAC and 400G QSFP-DD breakout DAC cable. The below table shows the detailed specifications of the 400G DAC cable.

FAQs about 400G QSFP-DD DAC Cable

Q: Can custom 400G QSFP-DD DAC based on customer needs?

400G DAC length can be 100% customized based on customer needs. But please expect a longer lead time for this customized product.

Q: What are the applications of 400G DAC?

The 400G DAC is mainly used for short-haul applications like the link between switches/routers within racks and adjacent racks.

Q: Can I plug 400G QSFP-DD DAC into an OSFP port?

A: No, because they are different form factors. You should plug 400G QSFP-DD DAC into the 400G QSFP-DD port and 400G OSFP DAC into the OSFP port.

Q: Can I plug 400G QSFP-DD DAC into a QSFP28 port?

A: No, 400G QSFP-DD DAC is incompatible with the QSFP28 port.

Q: What’s the difference between 400G AOC and 400G DAC cable?

A: The main difference is the media type. DAC uses a copper cable, while AOC uses fiber cable. 400G DAC is much cheaper than 400G AOC in the market.

Q: What are the QSFP-DD means?

The QSFP-DD means Quad Small Form-Factor Pluggable Double Density, and it is an enhanced version of the existing QSFP form factor.

Q: Is it possible to have an OSFP on one end of a 400G link and a QSFP-DD on the other?

Yes. The OSFP and QSFP-DD describe the module’s physical form factor. OSFP and QSFP-DD modules can communicate with one other if the Ethernet media types are the same (for example, if the link is 400G-DR4 or 400G-FR4, etc.).

Q: What is the difference between a 400G DAC and a 400G breakout DAC?

A: They have a different connector on another end. 400G DAC has a QSFP-DD connector on both ends, while 400G breakout DAC has a QSFP-DD connector and hybrid connector (like QSFP28, QSFP56, or SFP56) on another end.

In addition, the data speed on the other end is also different. Both ends of the 400G DAC support 400Gbps speed, while the 400G breakout DAC splitter 400Gbps to 8x50Gbps, 4x100Gbps, or 2x200Gbps on another end.

Q: Can I use 400G AOC instead of 400G DAC?

A: Yes, if you do not care about the pricing. 400G AOC is much more expensive than 400G DAC. We suggest you use DAC for short links <3m and AOC for the long links.

Q: What’s the benefit of using a 400G DAC rather than a 400G AOC?

A: 400G DAC is much cheaper and easier to deploy than 400G AOC. 400G DAC is also suitable for very short links, while 400G AOC is more commonly used for long-haul applications.

It's important to check the specifications and compatibility of the QSFP-DD DAC cable with your networking equipment to ensure proper functionality. Additionally, advancements in technology may have occurred since my last update, so it's advisable to refer to the latest documentation and specifications provided by the manufacturer. 

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