The ITU approved DWDM band extends from 1528.77 nm to 1563.86 nm, and divides into the red band and the blue band. The red band encompasses the longer wavelengths of 1546.12 nm and higher. The blue band wavelengths fall below 1546.12 nm. This division has a practical value because useful gain region of the lowest cast EDFAs corresponds to the red band wavelengths. Thus, if a system only requires a limited number of DWDM wavelengths using the red band wavelength yields the lowest overall system cost.