Transmitting signals at multiple wavelengths through the SAME Fiber with close spacing. Channel spacing usually is 200GHz or less in Frequency units, corresponding to 1.6nm in Wavelength units at 1550nm. The Transmission of many of closely spaced wavelengths in the 1550 NM region over a single optical fiber. Wavelength spacings are usually 100 GHz or 200 GHz which corresponds to 0.8 nm or 1.6 nm. DWDM bands include the C-Band, the S-Band, and the L-Band.