 With OS2 fibers the water peak problem is overcome, and all possible 18 channels can be used.WDM, CWDM and DWDM are based on the same concept of using multiple wavelengths of light on a single fiber but differ in the spacing of the wavelengths, number of channels, and the ability to amplify the multiplexed signals in the optical space.EDFA provide an efficient wideband amplification for the C-band, Raman amplification adds a mechanism for amplification in the L-band.