 Prior to the relatively recent ITU standardization of the term, one common definition for CWDM was two or more signals multiplexed onto a single fiber, with one signal in the 1550 nm band and the other in the 1310 nm band.In 2002, the ITU standardized a channel spacing grid for CWDM (ITU-T G.694.2) using the wavelengths from 1270 nm through 1610 nm with a channel spacing of 20 nm.ITU G.694.2 was revised in 2003 to shift the channel centers by 1 nm so, strictly speaking, the center wavelengths are 1271 to 1611 nm.