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Technology evolves at a rapid-fire pace. That’s why we’ve built an easy-to-use glossary to help you better understand the terms, technologies and trends that impact your business.


What is QSFP-DD?

QSFP-DD represents the advancement of the QSFP form factor, with "-DD" denoting double density. This latest iteration is the next-generation of this high-density, high-speed pluggable module form factor. In the case of QSFP-DD, its electrical interfaces utilize eight lanes, with each lane operating at a speed of 50 Gbit/s using PAM4 modulation. 


Why is QSFPDD important?

QSFP-DD meets the industry demand for higher-density, higher-speed networking solutions, and its physical format is designed to be compatible with QSFP ports from earlier generations. 


What are the advantages of QSFPDD?

Enhanced speed

QSFP-DD transceivers achieve a 4x increase in port speed (as compared to QSFP28) by combining double density and PAM4 modulation. As a result, QSFP-DD extends the capabilities of the QSFP form factor to support higher speeds of 400G, 800G, and 1600G. 

Increased lane density

When it comes to system port densities, QSFP-DD and QSFP28 transceivers offer identical performance. However, the key distinction lies in the fact that each QSFP-DD port can support 8 electrical lanes instead of only 4, effectively doubling the number of ASIC ports it can support for existing interfaces like CAUI-4. 

Backward-compatible form factor

QSFP-DD transceivers share the same form factor as QSFP28 and QSFP+ optics. This means that network elements such as switches and routers can be software upgraded to support higher rates (e.g., 400G). Consequently, these elements are fully prepared to incorporate QSFP-DD transceivers into existing systems to achieve their necessary media and reach requirements. 


Learn more: 

Blog post: Data centers and the move to 400G 

Discover EXFO’s solutions for testing QSFP-DD optics:

FTBx-88480 Series: compact, dual-port 400G testers 

FTBx-88800 Series: 800G test solutions for the lab