 a BER of 5 x 10-4 (i.e., the require- ment for systems using FEC, see Section 5.8.5.5) versus distance for propagation over an SSMF and detection MSE (2) using a PIN photodiode of an NRZIM-DD system using FFE-DFE electronic equalizer at the receiver. Also the performances of a Viterbi algorithm-based MLSE com- pensator are reported. System parameters are reported in Table 6.1 but for fibers parameters that are reported in Table 4.1. (After Xia, C. and Rosenkranz, W., IEEE Distance (km) Photon. Tech. Lett., 19(13), 1041, 2007.) Telecommunication Networks As discussed in Section 5.8.3.1, Viterbi algorithm changes the statistics of errors after the compensator; thus, the effect of the FEC cannot be evaluated assuming independent errors. Several studies are ongoing to determine exactly the impact of this element and to find an optimum design for the overall MLSE + FEC system, and probably this difficulty will be soon overcome with a global design taking into account both the elements together. Even more effective results can be obtained using pre-distortion of the transmitted signal through a look-up table designed to compensate both linear and nonlinear signal distortions. This method is not easy to implement and to control during system working, but it is very high performing, as it is demonstrated, for example, in [18]. The performance of a mix look-up table and linear electronics equalizer are reported in Figure 6.11 [18], where a maximum distance of more than 500 km is foreseen with only signal pre-distortion in pure linear propagation. Let us now assume that chromatic dispersion has been completely canceled. In this case limitations arise to the transmission reach from PMD and SPM. Let us start to assume transmission at low power, SO that SPM is negligible, and to oper- ate with a fiber installed before the discovery of the importance of controlling the PMD (a lot of fiber installed before the years 2000 are manufactured with processes that can produce a high PMD). Thus, let us assume the parameters of an SSMF