ed on TDMA. Recently WDMA has also been considered and a couple of products appeared on the market using this technique. Differently from TDM PONs that are standardized in detail by ITU-T and IEEE, no con- solidated standard still exists for WDM-PON, and this is an obstacle for the development of this kind of access system. In any case, ITU-T also works on WDM-PON standards and a first set of elements have been already defined, even if we are far from a rich standard like those for TDM PONs. 11.2.1 TDM PON Classification An extended standardization activity has been carried out on TDM-PON by a dedicated group of ITU-T, called full service access network (FSAN). Different standards follow the evo- lution of both optical technology and switching protocols, passing from APON and BPON, based on ATM, to GPON, capable of conveying multigigabit signals using either ATM or Ethernet protocols, thanks to its adaptation layer called GEM (GPON encapsulation method). The New Access Network Systems and Enabling Technologies TABLE 11.1 Summary of the Main Parameters of the ATM PONs, Ethernet PON, and GPON Channel Protocol Data Rate Reach Split Ratio Standard Insertion Loss Ethernet 1.25 Gbit/s 1000BASE-PX10-10km IEEE802.3ah (Power budget) symmetrical Normal PX-10U-23 dB 1000BASE-PX20-20km PX-10D-21 dB Permitted PX-20U-26dB PX-20D-26 dB 622 or Maximum 20km ITU-T 983.3 Class A: 20 dB 155 Mbit/s Maximum Class B: 25 dB Downstream Class C: 30 dB @1490 nm 155 Mbit/s Upstream @1310nn ATM or 2.488 or Maximum physical ITU-T 984.2 Class A: 20dB Ethernet 1.44 Gbit/s reach km Maximum Class B: 25 dB Downstream Class B+: 28 dB 2.488 or Typical Class C: 30 0dB 1.44 Gbit/s or 622 or 155 Mbit/s Upstream Several North American carriers are looking to GPON to advance their FTTx rollout efforts SO that GPON access is under deployment besides the older BPON infrastructure that is present in few local areas. A different situation exists in Europe, where incumbent carriers generally have not yet committed to a clear strategy. However, a great number 