With the recent USF Order from the FCC, one of the key takeaways was a discussion between the FCC and engineering firms that are designing Fiber to the home networks. The position of the engineering firms was that the FTTH networks they are designing were more expensive than the funding provided by the Alternative Connect America Model (A-CAM). The engineering firms had designed Gigabit-Passive Optical Networks (G-PON) with centralized splitters. The FCC stated that A-CAM assumes a G-PON with splitters in the field. Therefore the FCC says that the costs for that type of network are much lower than one with centralized splitters. A G-PON with splitters in the field would meet the speed requirements of the USF order of 10 Mbits/s down and 1 Mbits/s up and even the next tier of speed being discussed of 25 Mbits/s downstream and 3 Mbits/s upstream. It seems that this assumption will be driving much of the design considerations service providers make and the future of research to support continued passive optical networks.
G-PON is a mature technology that has been around for many years and has seen many deployments across the world. It supports triple-play services, bandwidth speeds in aggregate of 2.488 Gbits/s downstream and 1.244 Gbits/s upstream. One fiber strand is split to provide services to 32, 64, or even in some cases 128 subscribers. Three wavelengths of light are used, one for downstream data, one for upstream data, and one for video. The fiber strands can be up to 20 km long.
After G-PON, the next standard to come out for passive optical networks was XG-PON1. It provides for 10 Gbits/s downstream and 2.5 Gbits/s upstream and can coexist with G-PON by making use of different wavelengths of light. It has seen limited deployment because it did not meet enterprise needs for symmetrical bandwidth, and newer standards were already in the works that provided more significant bandwidth increases.
The newest passive optical networking standard is XGS-PON. It was created to provide an intermediate step for moving from G-PON to NG-PON2. It uses the same wavelengths as XG-PON1 but provides symmetrical downstream and upstream bandwidth of 10 Gbits/s. It should allow for service providers to meet enterprise needs while still coexisting with existing G-PON deployments. It also uses some of the management standards developed for NG-PON2.
On Thursday we’ll take a look further into the future and see how fiber networks will continue to change.