at 1,310 nm and 1,550 nm. The channel spacing of Wide Wavelength Division Multiplexing (WWDM) is 50 nm or more. Any channel spacing greater than 50 nm is called wide wavelength division multiplexing. The first optical window at 1,310 nm and the second optical window at 1,550 nm are used for transmission. The two wavelengths are related to the first WDM plans, which provided only these two wavelengths. Transmission is separate over the two wavelengths, which are separated at the end of the transmission link. For comparison, the difference to Coarse Wavelength Division Multiplexing
(CWDM) will be clarified, which works with eight resp. eighteen wavelengths and a channel spacing of 20 nm. Wide Wavelength Division Multiplexing was discussed in the context of the 10 Gigabit Ethernet standardization, 10GbE. WWDM technology is used, among other things, in the non-standardized 10GbE interface 10GBase-EX4.