tes and traditional terrestrial television, and the customers are used to having the first for steadily decreasing prices, and the second for free. Moreover, where a diffused cable TV exists, like in the United States, the IpTV is per- ceived by the customers as something they already have and it is difficult to obtain from it the marginal increase that the carriers need. Finally, the importance that pair-to-pair customer activities are assuming, is something that puts value in the intrinsic bidirectional nature of the telecommunication network; thus, it can be a good opportunity for carriers. This consideration also points the attention toward the weaker aspect of the GPON, as we have seen in the example of the last section. Thus, a great amount of work is being undertaken in the standardization bodies (mainly in the ITU-T FSAN group) to standardize one or more versions of the so-called NG-PON (Next Generation PON). Since the deployment of the GPON in vast areas is considered certain, all the work is based on the assumption that the new access transmission equipment, while providing a much greater capacity, exploits the same ODN deployed for GPON. Besides this simple, but important requirement, a group of carriers in ITU-T have pro- posed that the entire standardization of the NG-PON be based on a much more severe set of requirements targeting a smooth and gradual transition from GPON to NG-PON. This set of requirements, that can be called Compatibility Conditions (CC), can be synthesized as follows [16]: Coexistence: NG-PON systems need to coexist on the same fiber with today's GPON Allows existing GPON subscribers to be individually migrated to NG-PON on an as-needed basis without disrupting other users on the PON Relies on the deployment of G.984.5 compliant ONTs today and NG-PON sys- tems using G.984.5 enhancement band wavelengths Digital capacity: At a minimum, the capacity of NG-PON systems should be 10 Gbit/s downstream and 2.5 Gbit/s upstream. Alternatively, a system that over- lays multiple GPON systems