Dense wavelength division multiplexing (DWDM) is a Technology that uses multiple wavelengths to transport a vast number of separate channels. In this monograph, the combined effect of important fibre nonlinearities (stimulated Raman scattering, SRS and four wave mixing, FWM) in the presence of amplifier noise and receiver noise has been studied at different data rates. The optimization of the system parameters has been done considering SNR and BER. The investigations were repeated considering specifications of two commercially available fibres also and these results validated optimized values of system parameters calculated earlier. Subsequently, two general equations have been formulated to calculate SNR from inter-amplifier separation, as well as, system length. To simplify the calculations, specific equations, corresponding to fixed set of inputs, have also been obtained with the help of curve fitting.The advantage of the general equations is their versatility and of the specific equations is less computation complexity. The results presented in work are expected to be useful for the design of an efficient optical DWDM system.