acing, the link length, the span length, and SO on. This means to position the DWDM product in a well defined category of DWDM systems. Power budget: Starting from the first system specifications the optical power profile along the line is determined, thus selecting the components to use. At the end, the optical SN ratio is determined. 3. Dispersion map: Determining the dispersion map, that is, the distribution of disper- sion compensating elements along the line and, in case, the presence at the trans- mitter and at the receiver of equalization components is a key step. It influences not only the system behavior versus chromatic dispersion, but also the impact of nonlinearities and of PMD, that in the majority of cases is equalized by electronic adaptive equalizers contemporary to chromatic dispersion. 4. Penalties impact: Using the penalty addition rule all the relevant penalties are added to the ideal SNo (driven only by ASE noise) to arrive to a required SNo that takes into account all the relevant phenomena. If the required SNo is smaller or equal to that estimated performing the power budget the design can go on, other- wise some elements has to be changed to match the required performance. 5. Simulation: The design is confirmed via simulation to understand the impact of the numerous approximations. 6.3.2.1 Erbium-Doped Optical Fiber Amplifier Amplified Systems Design 6.3.2.1.1 Power Budget In long-haul systems, EDFA amplifiers work in deep saturation, since this allows both power stabilization along the line and minimum signal distortion. In this condition, in-line amplifiers are characterized by an output saturation power Pout that corresponds to an input saturation power Pin. This means that every in-line amplifier will inject into the line a power equal to ac pout where is the coupling loss that in general is very small. At the amplifier input, the power would not be lower than due to the fact that the saturation condition has to be maintained. Moreover, extra losses that are located before the booster 