in GPON are specified in the standard, SO as to be able to match the required performances. In the case of B+ and C classes, the situation is different. As a matter of fact, modal disper- sion arises in the downstream link [7], constituting a first span limitation. In order to face this effect, two ways are possible. The most diffused solution is to substitute FP with distributed feedback lasers (DFBs), accepting a cost increase. Specific DFB lasers are designed for use in The New Access Network Systems and Enabling Technologies GPON, whose design requirements are relaxed with respect to similar devices used in dense wavelength division multiplexing (DWDM) long haul systems in order to reduce the cost. As a matter of fact, perfect single mode operation is not strictly needed to eliminate modal dispersion. As an alternative to DFBs, the adoption of Electrical Dispersion Compensators (EDC) in the OLT has been also proposed and demonstrated [8]. It is interesting to observe that standard forward error correction is practically ineffective to correct the effects of modal dispersion. As a matter of fact, when the fluctuation in the modal structure of the source causes errors, they are concentrated in long bursts. It is possible to design a code conceived to correct long bursts of errors [9], but these codes are generally not used in optical communications for the decreased effectiveness in correcting random errors. As far as the downstream is concerned, in order to achieve the required power budget with the standardized classes of emitted power, the ONU detector has to be an avalanche photodiode (APD). This also impacts on the cost of B+ and C GPON classes. Another important phenomenon appears when the analog video overlay is present. In this case, due to the relevant power of this new channel, the Brillouin effect arises [10] SO that a careful design of the optics is needed to reach the specified performances. 11.2.2.2 GPON Frame and Adaptation Protocol As in the case of all implementations of the TDM-PON, also in th