FEC FEC gain (RS 255,239) Required SN, This fact alleviates greatly nonlinear effects allowing a longer link to be designed. In both cases, however, nonlinear effects determine the maximum reach in the different situations. An interesting element to further quantify is the reach difference between the two models' results. Telecommunication Networks Optical power per channel (mW) Raman Position along the span (km) FIGURE 6.29 Single-channel power profile in a span of the ultra-long-haul system-based on hybrid amplification. Doing again the dimensioning and the penalty evaluation, but maintaining the link length as a parameter, it is found that at a link length of 8000km, the design SNo of the EDFA alone system comes out to be 23.8 dB, while the requirements coming out from the penalties evaluation is 22.0 dB. In this condition the draft design can be accepted waiting for the simulation results. Thus, with the longer link that can be realized with the EDFA alone technique and with our design choices is on the order of 8000 km long. Naturally, the design can be further optimized, for example, using more effective elec- tronic compensation, introducing pre-chirp to better manage nonlinear effects, optimizing both the duty cycle and the form of the transmitted pulse, besides an optimized dispersion map and better quality amplifiers. All these steps help to improve the system performances above what we have achieved with our simple design, but it is true for both the system architectures and the difference always remains. Moreover, the hybrid architecture presents possibilities that are not available if all the EDFA architecture is chosen. Raman effect can be used in a more distributed way sending the pump also in the SSMF used for transmission, both co-propagating and counter-propagating pumps can be used in the Raman amplifiers and, finally, all Raman amplification can be adopted, eliminating completely EDFA amplifiers and going much nearer to the optimum scheme of distributed amplification. All these steps, further 