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We’ve posted a number of blogs about Cisco Optics’s “Single-Lambda 100G” pluggable optics based on PAM4 modulation. At the beginning of the year we announced the first product in this series, the QSFP28 100G FR (Product ID: QSFP-100G-FR-S). We are excited to add a new addition to this series, the QSFP28 100G DR (Product ID: QSFP-100G-DR-S).
Single-Lambda 100G Optics
You may notice that there’s only one letter difference between the two products – “D” versus “F”. They both use Single-Lambda 100G technology based on PAM4 modulation. This means that they are optically interoperable with 400G pluggable optics that support 100G breakout, such as Cisco’s QDD-400G-DR4-S. That makes it easier for network operators to incrementally migrate their architectures from a 100G foundation to 400G. Furthermore, both the DR and FR optical specifications are standardized. Therefore, any future smaller 100G form factor that supports Single-Lambda 100G, such as SFP112, would be optically compatible with them.
DR versus FR
So what’s the difference between the two products? It’s the maximum length of fiber it can support, a.k.a. the reach. FR reach is 2km, while DR reach is 500m. At 500m, DR is great for applications inside data centers such as leaf-spine connectivity, where the fiber length seldom exceeds 100m, let alone 500m. DR complies with the IEEE standard 100GBASE-DR. At 2km, many service providers will find the FR to meet their needs for longer distances that don’t require 10km reach optics. FR complies with the 100G Lambda MSA 100G-FR standard. The IEEE is also close to releasing a 100GBASE-FR1 standard, which this product will also comply with.
If you’re wondering what it is about the DR and FR transceivers that makes them support different reaches, it’s the transmitter signal power levels and receiver sensitivities. They’re tuned for their respective distances over single-mode fiber. Experts in the IEEE and the 100G Lambda MSA thought this through in painstaking detail to come up with the details of the optical specifications. So network operators only have to worry about is the distance of their links.
Special thanks to Cisco engineers, some of whom lead the aforementioned standards bodies, put a lot of blood, sweat, and tears into the design so that you don’t have to.
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Great write up – thanks Pat. Probably one of the most straightforward, easily digestible and understood explanation of this topic that i have read!
Thank you David! Glad it’s helpful.