 effects [29,30]. In any case, in-line dispersion compensators have to be used due to the presence of nonlin- earities. In a very long link, not only dispersion, but also nonlinear effects accumulate with the distance. Once a strong nonlinear distortion has been accumulated, the pulse cannot be reshaped via linear compensation and also dispersion compensation is no more possible. Thus, dispersion has to be compensated in-line SO frequently that no sensible nonlinear degradation accumulates between two nearby compensators. In order to evaluate the effectiveness of nonlinear effect accumulation, the effective length Le is often used in unrepeated systems. The same can be done in the presence of amplifiers; since each amplifier rises the power of the optical signal, nonlinear effects could start after each amplifier SO that the effective length of the amplified link is Le=na Leo, where Leo is the effective length of a passive fiber link and na the span number. The only case in which in-line dispersion compensation is not needed is the case in which a new technology called electronic dynamically compensated transmission (EDCT) is used. In this section we will first analyze the approach through in-line linear compensa- tion and after that we will describe EDCT. In practical systems in which in-line compensation through DCF or fiber Bragg grating (FBG) is used, the amplifiers distance is sufficiently short to allow dispersion compensat- ing modules (DCMs) to be located in the amplifiers sites, generally in between the stages of a multistage optical amplifier. Telecommunication Networks TABLE 6.3 Parameters of a DCF Attenuation (dB/km) Dispersion (ps/nm/km) Dispersion slope (ps/nm2/km) Nonlinear index (m ²/W) 2.6 X 10-20 Effective area (um2) Three techniques can be used for in-line dispersion compensation: 1. Pre-compensation: The compensation module is at the beginning of the span; this means that a DCM is placed at the booster site to compensate the first span 2. Post-compensation: The compensation module is at the en