Migration from G(E)PON to NGPON

Economic feasibility was the main obstacle for the fast implementation of FTTH networks. But nowadays, when there are more than 30 million FTTH connections in the world, it is clear that the previous settings amended. In this paper, we discuss how and where to find the economic efficiency; the answer is PON networks. After that, it will be shown why GPON has a small advantage over GEPON. At the end of paper, there is presented an analysis of wavelength spectrum of classical PON and NG PON and we have showed that the upgrade from the classical PON to NG PON is possible. This upgrade has two main requirements from ODN (Optical Distribution Network). It is the coexistence of two types of PON, classical PON, and NG PON, on the same PON tree; and using of optical infrastructure (without any intervention) of classical PON.