nication Networks In order to carry out a comparison that should underline the advantages of the hybrid solution with respect to solutions based on EDFA alone, we want also design an ultra-long- haul link completely EDFA-based with the same parameters. In this case the SN is given by (6.82) where the booster amplifier is supposed to be a single-stage EDFA, post-compensation DCFs are used, as in the hybrid case, and the last EDFA is different to arrive with the cor- rect power on the APD. Also, in this case optimization is carried out with two constraints; the maximum power constraint is expressed by Equation 6.74, while the constrain relative to the power on the receiver is GpPMarec = Pred (6.83) After that, the design procedure is identical to the used from the design with hybrid amplifiers. All the results of the hybrid amplification design and of the two stages EDFA design we have achieved up to now are summarized in Table 6.8. The characteristics of the selected components and the output of the draft design allow us to evaluate the SNo at the link output that comes out 25.4 dB for the hybrid solution and 22.8 for the all EDFA solution. In both cases the FEC gain has not been accounted for, it will be considered in the penalties analysis. A first advantage of the hybrid solution is revealed by these figures: the lower noise fac- tor of the Raman amplifier and the automatic compensation of the DCF loss allow the ASE noise to be quite reduced. 6.3.3.2 Ultra-Long-Haul Transmission Systems: Penalties, Evaluation, and Simulation Results Let us now define the target SNo on the ground of the various transmission impairments in both the cases we have considered. The detail of the penalty evaluation in the two cases is reported in Table 6.9, where 21.5 dB is obtained for the hybrid solution and 23.8 dB is obtained for the EDFA solution. Thus, the 10,000 km long link can be realized with the hybrid technique (the draft design SNo was 23.5 dB) but not with a pure EDFA architecture (the design SNo was 21.5 dB). This also 