When we launch our portfolio of 200G and 400G optical transceiver solutions later this month, the available options may seem unfamiliar at first. Many of the operating standards are new, and so are the form factors. In this article, we’ll talk through the differences between the two leading contenders, and why it might make sense to pursue one over the other.

What are my form factor options?

There are two primary options available: QSFP-DD and OSFP.

QSFP-DD and OSFP optical transceivers

The two form factors differ very slightly in size. The OSFP is slightly wider and deeper than the QSFP-DD. As such, the OSFP has a lower port density on a standard 1RU faceplate than the QSFP-DD (32 and 36, respectively).  

What differences should I look out for?

Let’s start with what’s the same. The electrical interface on each form factors uses 8x50G lanes with PAM4 modulation. On the optical side, depending on the standard, you will see either 8x50G or 4x100G PAM4.

Other than the size, the biggest differences are in power consumption and heat dissipation. The maximum power consumption of the OSFP is 15W, while the QSFP-DD’s is 12W. The OSFP also incorporates thermal management directly into the form factor, while the QSFP-DD does not. The port density and power consumption differences may make the QSFP-DD a more attractive option for data center customers.

Which one should I choose?

Beyond the technical pros and cons, the decision may largely depend on your deployment timeline; in other words, how much you need to look backwards vs. how much you can (or want to) look forward. The QSFP-DD offers direct backward compatibility with both QSFP and QSFP28 optical transceivers, while the OSFP requires an adapter to support QSFP optics in an OSFP cage. As such, if you’re planning on rolling out 400G sooner and phasing it in gradually, the QSFP-DD options will make a lot of sense.

However, if your 400G needs are not immediate, you may want to consider OSFP. Because many industry experts anticipate that OSFP will offer an easier pathway to 800G (with associated backward compatibility), OSFP may be a stronger contender in the long-term.

Want to explore the ins and outs of these new optics even further? Our experts are available for a complimentary consultation.

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