 arrive at a total unilateral optical bandwidth of Bo = 20 GHz (0.16 mm at 1550nm wavelength) with The use of a FEC is almost obliged in long-haul systems and we choose the standard ITU-T FEC: the RS (255,239) that in the ideal conditions provides 6 dB of code gain. Using Equations 6.65a and 6.65b it is easy to verify that the power budget equations for the transmitter and the receiver can be satisfied with standard DWDM quality compo- nents (see Chapter 4, the main parameters of transmitter and receiver are summarized in Table 6.1). The total ASE power is -16.4c dBm per channel, SO that the ideal SNo is 24 dB and the ideal SN, = 24 dB (if M22 SN, 2 SN). This gives quite a margin with respect to the required 11 dB (17 from the receiver with = 2 minus 6 dB of code gain) that allows the allocation of more than 8.8 dB for extra penalties due to various impairments. The last thing to do is to select the dispersion map. We have to design quite a standard link, following literature, we will adopt a post-compensation map with a certain degree of under compensation and a per channel FFE-DFE equalization of the residual dispersion at the receiver. Following a simple map optimization, where the only parameter to setup is the under compensation, we will under compensate for 00ps/nm implying a differential delay of 493 ps in the signal bandwidth and will adopt a nine taps FFE-4 tap DFE adaptive equal- izer. This allows the residual dispersion to be almost completely compensated at the receiver and the SPM effect to be attenuated. Transmission Systems Architectures and Performances 6.3.2.1.4 Erbium-Doped Optical Fiber Amplifier Amplified Systems Design: Penalties Impact Once the DWDM system has been specified fixing its main parameters, the system power budget and dispersion map have been designed, and all the tentative specifications for the main components have been set, it is time to start to verify if the design is sufficiently robust versus all the performance impairments to meet the performance requests, that, in genera