cal expression of the noise variance. At this point, an algorithm is available relating the parameters to be optimized, that is, the DCF dispersion and dispersion slope and, in case, the span length, with the link qual- ity factor. Thus, a numerical optimization procedure is used to find the optimum parameters com- bination. Among traditional nonlinear optimization methods [35] the Nelder-Mead opti- mization procedure, also called nonlinear simplex method, seems particularly suitable for this case in which the evaluation of the objective function is quite complex [36]. Naturally, due to the fact that any optimization will require several simulation execu- tions, a key point is to use a computationally simple simulation procedure; thus, the expe- rience in balancing accuracy and approximations intended to simplify the computation is a key point for this optimization procedure [37,38]. Generally, when optimizing the system, more than one local optimum exists and the choice is often guided more by the stability of the working point than by extreme optimi- zation of the system length [31]. As a matter of fact, when implementing a design in a practical system, several consider- ations, besides pure performance optimization, lead the implementation choices. One of these elements is the stability of the chosen solution versus small variations of the design parameters, variations that can be caused both by tolerances of the components' charac- teristics and by aging. Telecommunication Networks Another important point is the comparison between NRZ and RZ modulation. In the case of unrepeated dispersion-limited systems, RZ performs better than NRZ. This behav- ior is even more evident in single channel optically amplified links, due to the robustness of RZ modulation to ISI due to pulse spreading. In this case, it is even possible to improve pure RZ performances by transmitting chirped pulses to achieve more robustness to residual dispersion. To give an example, let us consider long-haul system with length of about 4600 km