Originally, the term coarse wavelength division multiplexing (CWDM) was fairly generic and described a number of different channel configurations. In general, the choice of channel spacings and frequency in these configurations precluded the use of erbium doped fiber amplifiers (EDFAs). 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.