QSFP-DD vs OSFP: From 400G to 800G and Beyond in the Data Center

400G isn’t just for hyperscale data centers anymore. With newer Intel and AMD architecture machines on the market, it is not uncommon for each server to push more than 10G northbound. In turn, Top of Rack (ToR) or End of Row (EoR) switches need enough uplink capacity to the Spine/Leaf or Core switches to ensure that there are no network bottlenecks.

Great, so you have a need for 400G in your Spine/Leaf or traditional L2 network. Which technology do you choose?

On the Spine/Leaf and Core network switch side, there are two main options: OSFP (currently championed by Arista) and QSFP-DD. The latter has a slight operational advantage today. In most cases, QSFP-DD is directly backward-compatible with current QSFP28 (100G) optics, while OSFP requires an adapter to plug into legacy QSFP28 ports.

QSFP-DD and OSFP optical transceivers for 400G applications in the data center.
400G OSFP and QSFP-DD Optical Transceivers

However, this capability will depend on the switch or router vendor, as ports will have to negotiate lower speeds. You will need to check with your switch or router vendor to ensure that 400G ports will support 100G QSPF28 optics, copper Direct Attach Cables (DACs), and Active Optical Cables (AOCs). Some switches are even backward-compatible to 40G QSFP+ as well (again, subject to specific switch/router capabilities).

800G and Beyond

So how does 800G or Terabit Ethernet factor into this decision?

Most enterprises operate on a 3-5 year equipment replacement lifecycle. In 3 years, 800G will be a reality, and 1.x Tbps per port may even be available as well. Servers are only going to increase in capability. Today, 25G server ports are becoming more common, especially in Hadoop/HBase or other BI, datamining, and reporting applications.

The advantage OSFP has over QSFP-DD is its power per port, which may come into play when using longer-haul optics, e.g., CWDM and future products like ZR and ZR+. It is not clear if QSFP-DD will be a viable option for these longer-haul 800G applications, or any application beyond 800Gbps due to power constraints. If this is indeed the case, the extra power/heat dissipation characteristics of OSFP would offer a bit of insurance.

The good news is that these form factors can interoperate. For example, a Spine switch with an OSFP port and optic can communicate with the QSFP-DD port on a Leaf or ToR switch. Both interface types operate electrically at 8 X 56G SERDES (usable 8×50), and can be broken out to 4x100G, 2x200G or 8x50G with the appropriate cabling solutions.

The Champion ONE family of brands specializes in helping our customers transition their networks into the future and avoid potential barriers to the right network evolution. Ready to start preparing your network for 800G and beyond? Schedule a meeting with our experts to learn more.

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