In terms of transmission technology, 400GbE relies on optical fibers, both multimode fibers and single- mode fibers. The CWDM method is used for wavelength division multiplexing. The possible distance ranges are between 100 m with multimode fibers and from 2 km and 5 km with monomode fibers. The bridgeable distance with single mode fibers depends on the OS class. Transmission takes place with wavelength division multiplexing according to CWDM over 4 lanes with 100 Gbit/s, 8 lanes with 50 Gbit/s or 16 lanes with 25 Gbit/s. The corresponding interfaces have the designations 400GBase-SR8 and 400GBase-SR16.