x situations arise when dynamic devices as some optical add drop multiplexers (OADMs) are used. Thus, at the end both loss and dispersion are compensated, respectively, by optical amplifiers and DCFs. Now we will apply all the methods introduced in the last sections to assess the perfor- mances of the system sketched in Figure 6.18 when EDFA amplifiers are used. The noise contribution at the receiver will be mainly caused by amplifiers amplified spontaneous emission (ASE) accumulation, since the presence of a preamplifier will make the received signal quite more powerful than in unamplified cases. Moreover, a PIN is Transponder Transponder Demux Booster In line-amp Pre-amp Transmitted Received Optical power distribution along the line FIGURE 6.18 Block scheme of a long-haul DWDM system and optical power distribution along the line. Telecommunication Networks generally used at the receiver since further amplification after the preamplifier is not needed. In order to determine the electrical noise, let us consider the transmission line like a cas- cade of amplifying and attenuating elements. In this simple model, let us imagine that all the in-line amplifiers are equal and that the net gain resulting from the two stages and the attenuation due to the interstage loss exactly compensate the loss of one span. In real systems, the amplifiers are generally hosted in preexisting locations where the carrier has a point of presence. These locations could not be at the same distance, one from the other; thus, a more complicated situation arises. We will evaluate later the characteris- tics of a chain of amplifiers that are not at the same distance. A single double stage amplifier with an interstage loss has a noise figure NFtotal=NF1 (aG1) (compare Section 4.3.1.4) and it is optimized SO to minimize the overall noise figure for the considered loss. Thus, we will assume that all the in-line amplifiers are optimized for the correct value of the DCF loss and have a noise figure equal to NFil. The system will have also a booste