Napatech A/S : QSFP-DD, the new ‘kid’ on the block

Backward Compatibility and shared form factors between speed tracks

The CFP2 form factor was introduced as a dense successor to the CFP. As mentioned in the 100GBASE-LR4 case study above, the CFP2 form factor supports both the CAUI-10 and the CAUI-4 host side interface, making it the first form factor to span two speed tracks in the Ethernet roadmap, the 'Highly Parallel Speeds'- and the 'Quad Speeds' track. Being a new form factor, the CFP2 however didn't do well in terms of backward compatibility with existing link speeds. The newly introduced QSFP-DD form factor spans the same two-speed tracks, but is additionally also backward compatible in the 'Quad Speeds' track with previous QSFP standards, QSFP+ and QSFP28. Backward compatibility is enabled by a brilliant doubling of the supported number of host interface lanes through a 2^nd row of contacts in the module interface, as seen in Figure 3.