and the ONU is colorless. Thus, the management of the spare parts and in general the system maintenance is simplified. 11.2.4 XG-PON Another straightforward idea in preparing the network to meet a great increase in bandwidth request is simply to increase the bit rate from 2.5/2.25Gbit/s to, for example, /2.5Gbit/s. Telecommunication Networks This is the way that has been preferred for standardization by FSAN. After finalizing the XG-PON1 basic specification, FSAN successfully carried it to ITU-T and the set of requirements was standardized as in the G.987 series. The important choice in anticipating the standardization of the architecture relying on an higher bit-rate to achieve a greater capacity was not done arbitrarily, on the contrary, all the solutions presented by FSAN members or known in literature have been evaluated especially from the point of view of the asymmetry between the real per user bandwidth, and the XG-PON has been evaluated as the most suitable with the most common bundles of services [19]. Moreover, the design has been built on the requirements of the CCs, SO that an XG-PON can be installed on an ODN where a normal GPON is running without disrupting the GPON operation. These requirements have conditioned the choice of the spectral plan of the XG-PON, bringing us to the solution reported in Figure 11.10. Three classes of XG-PON are foreseen even if the standardization mainly concerns the first class, which is considered the first to be deployed. 1. XG-PON1 a. NRZ both upstream and downstream b. Downstream, =9.95328 Gbit/s C. Upstream, R=2.48832 Gbit/s d. Maximum fiber distance: 20km, with options of 40km (in case with optical amplification) e. Split ratio up to 1:256 f. Loss budgets: 29 and 31 dB FEC in the frame to help correct transmission both upstream (RS(248, 232) ) and downstream (RS(248,216)) 2. XG-PON1 Extended a. As XG1-PON, but with a longer reach; this solution will probably need the so- called extenders, which are amplifiers suitable for remote power feeding 3. XG-PON2 a. Has to t