I was in Munich last week for the FTTH Council Europe conference and engaged in a number of interesting conversations with vendors and operators on the issue of NGPON 2, a technology that could be deployed over fiber networks.
Operators are currently discussing in the FSAN pre standards body which technology will be chosen for NGPON 2. Following the FSAN decision, expected in April, the technology can then go into the standardization process in the ITU and commercial systems can be developed. NGPON 2 will be the most advanced technology for fiber networks beyond today’s widely deployed GPON and EPON systems and the XGPON 1 and 10GEPON systems that are already commercially available.
The choice of technology will have a big impact on vendors who are backing a variety of options and will also have consequences for operators looking to upgrade their networks in future years. The three basic candidates for NGPON 2 are pure WDM PON systems (of which there are a number of variants), hybrid TWDM PON and UDWDM PON. But it is the hybrid TWDM PON and UDWDM PON systems which are leading the race.
Pure WDM PON solutions appear out of the game
Most pure WDM PON systems require alterations to the outside plant, which many operators are loathe to change when it is already providing working services. Generally speaking, they are constrained in reach to around 25km, not much more than today’s GPON systems. WDM PON systems might also suffer in terms of coexistence with existing technologies. For example, the WDM PON systems may use the C band which a number of important FTTH operators such as Verizon, NTT and Portugal Telecom are already using for RF video overlay.
Hybrid TWDM PON and UDWDM PON lead the way
The two leading candidates for NGPON 2 are NSN’s NGOA UDWDM PON solution, using coherent technology from the transport network and seeking to merge the access and aggregation networks and the hybrid TWDM PON system backed by Alcatel Lucent and Huawei. The hybrid system stacks four XGPON 1s onto the same physical fiber. Each subscriber receives all four wavelengths and the technology does not offer a dedicated wavelength to each subscriber, unlike the UDWDM PON system.