nd assuming to use a nine taps FFE and a nine Taps DFE plus a 13 bit look-up table, the system can reach the impressive distance of about 13,000 km and adding also Raman co-propagating pumps in the SSMF in order to avoid excessive signal attenuation that request EDFA amplifiers, it is possible to go over 15,000k However, such a complicated system, using a complex digital signal processor (DSP) per channel at the transmitter, four Raman pumps per site, and no EDFAs has quite a high Transmission Systems Architectures and Performances CAPEX and OPEX and could be applied only in a very small number of cases, at least in terrestrial networks. 6.3.4 Single-Span Systems In practical networks, there are a certain number of systems that have to span a few hun- dred kilometers, too much for unamplified systems, but a short distance for the capabili- ties of long-haul systems with intermediate amplifier sites. It is to remember that increasing the number of points of presence in the network increases the operation expenses due to maintenance and other activities related to the point of presence. Moreover, in submarine networks avoiding submerged amplifiers is even more important, if possible. Thus, it is important to understand what is the potential performance of a system having amplification only at the terminals and no intermediate site. Since these systems have to span the maximum possible length, there are several pos- sible architectures that seem natural: using hybrid EDFA-Raman amplification and using the DCF also for enhancing Raman efficiency, using all Raman amplification to exploit also low Raman noise factor and more distributed amplification, or using complete link pre-compensation and amplifying through single-stage EDFAs. Moreover, the use of differential phase encoding is appealing in this kind of application due to the better receiver sensitivity. As examples we will design three 10 Gbit/s systems: two based on all Raman amplifica- tion, one using IM, the other differential phase shift keying (DPSK), the t