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All About 400G QSFP-DD

All About 400G QSFP-DD

When working with data centers, large enterprise networks, or anything else with comparable data demands, you need the best hardware. You can skip looking through bargain bins. You need the type of equipment that pushes the envelope of what engineers can produce at scale.

Naturally, this involves fiber optics for the backbone of your communications, but what kinds of fiber connections will you use?

At the very top of the hierarchy, you’ll find advanced QSFP that can hit data rates well into the hundreds of Gigabits per second. Among QSFP options, 400G QSFP-DD stands supreme.


A quad small form factor pluggable double-density (QSFP-DD) transceiver provides fiber and Ethernet communication for high-density networks. It supports data rates up to 400 Gbps, making it a prime piece of equipment for the very most demanding networks.

As we get into the features and specifications of this communication option (and as we compare it to common alternatives), you’ll see that QSFP-DD caters to top-end performance above everything else.

Key Features

Some of the noteworthy features in play for QSFP-DD include the ability to hot-swap along with backward compatibility with other QSFP form factors. DD is IEEE 802.3 compliant and provides MSA. It’s also known for breakout compatibility, meaning it can interface with plenty of 100G technologies.

Specs to Compare

In terms of hardware specifications, Cisco makes a range of QSFP-DD transceivers. They come in multi- and single-mode. Many transceivers operate with a maximum power consumption of as little as 1.5 W. They are capable of full duplexing, and across the fiber modes, they support cable runs ranging from a few meters to 40km.

Overall, QSFP-DD transceivers provide the raw capabilities you might need in tough environments and high-end applications.

How QSFP-DD Differs from Other QSFPs

To fully understand QSFP-DD, we can make clear comparisons to other QSFPs. Basically, DD is the latest and best version of the technology. The smallest transceivers are DD. They also achieve the highest data rates by a significant margin.


Taking a look at QSFP28, it’s a quad-channel communication stream. It uses the same form factor as DD (and the other version in the next section). Most notably, QSFP28 supports data rates up to 100 Gbps.

Considering these numbers, it won’t surprise you to learn that 28 is the oldest of the QSFP forms we’re discussing today. It also provides the lowest levels of performance.


Next up is QSFP56, and it’s basically an upgraded version of 28. Again, it uses the same form factor, and it runs on quad-channel communication. But, QSFP56 increases networking capabilities, and a few features help with this.

One feature is PAM-4 modulation which allows for better data management and gets total communication speeds up to 200G.

As a quick reminder, QSFP-DD supports 8-channel communication and it can achieve data rates up to 400G.

There are other QSFP versions out there, but these are the most comparable, giving the universal compatibility across the three versions.

Applications for QSFP-DD

Now that you know more about QSFP-DD, we can explore some of the best applications for this technology. As you already know, it’s a high-speed fiber setup, and that makes it great in networks that need the most raw speed and bandwidth.

The applications below won’t surprise you, but it’s important to understand exactly how and why this is a premier high-end technology.

Data Centers

Data centers have to come up first because they require the most bandwidth for communication. Data center networks are always pushing to further extremes in order to squeeze out faster transmissions and more total data movement.

QSFP-DD is perfect for this. You can utilize transceivers that support cable runs the lengths you need. At the same time, 400G is in the top echelon. It can support the most demanding data center networks, and with its cross-compatibility, it’s easy to fold into your existing infrastructure.

Enterprise Core

Another application that requires bandwidth is enterprise network cores. The core layer supports traffic for the entire enterprise network. It’s the layer that communicates between your endpoint devices and the greater internet. You need the best transceivers for this work.

You will also sometimes see QSFP-DD in the distribution layer. It’s the second-most demanding portion of an Enterprise network, so when demands are high enough, the distribution layer also needs 400G technology.

Service Providers

The last major application to consider is service provider systems. The sheer volume of data passing through service provider nodes dwarfs most applications, and you need enough bandwidth to manage it.

The same principles that make QSFP-DD good for enterprise cores apply to service providers. After all, these are ultimately very large professional networks with huge numbers of end users.

In the end, QSFP-DD represents one of the most powerful networking options on the market right now. It achieves gargantuan speeds across an array of distances. If your network needs the best, QSFP-DD should be on your radar.

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