ITU-T achieves industry first with new standards for 40 Gbit/s fibre to the home
ITU-T members have followed the recent approval of the ITU-T G.989 series of standards for 40-Gigabit-capable passive optical networks (NG-PON2) with the first-stage approval (“consent”) of ITU-T G.989.2 Amendment 1, a further update to the NG-PON2 physical layer specification. NG-PON2 is a major milestone in the field of access networking as the first series of standards to provide fibre-optic access speeds beyond 10 Gbit/s.
NG-PON2 is a product of ITU’s standardization expert group for networks, technologies and infrastructures for transport, access and home, ITU-T Study Group 15.
The new series of standards addresses operators’ need for common technologies to support the optical-access demands of homes and businesses, mobile backhaul and fronthaul and other applications. Major operators are testing NG-PON2 systems with the intention of deploying these systems in the near future.
NG-PON2 is based on a multi-wavelength, point-to-multipoint architecture, and its primary solution is time and wavelength division multiplexed PON (TWDM-PON). A typical TWDM-PON consists of four to eight wavelengths in both directions, achieving a maximum rate of up to 80 Gbit/s in each direction. Each wavelength is capable of providing a subscriber with optical access up to a rate of 10 Gbit/s, and the upstream/downstream wavelength is also capable of operating at the lower rate of 2.5 Gbit/s. The typical distance between the optical line terminal (OLT) and an optical network unit (ONU) is 40 km, and one OLT is capable of supporting up to 256 ONUs.
Operators implementing NG-PON2 will have the ability to reuse existing optical distribution networks (ODNs) deployed for previous generations of PONs. The wavelength plan of NG-PON2 provides for co-existence with G-PON (ITU-T G.984 series); XG-PON1 (ITU-T G.987 series); radiofrequency video overlay (ITU-T J.185; ITU-T J.186); and optical time-domain reflectometer (OTDR).
NG-PON2 is a successor to the 1-Gigabit-capable G-PON (ITU-T G.984 series) and the 10-Gigabit-capable XG-PON1 (ITU-T G.987 series), with key enhancements provided by multi-wavelength operation and ONU wavelength tunability in both transmitters and receivers. NG-PON2 specifies a group of physical parameters on ONU wavelength tuning characteristics and a message-based protocol to manage ONU wavelength assignment and switching. ONU management and control for NG-PON2 reuses ITU-T G.988, and its wavelength management follows the guideline in ITU-T G.9802.
ITU-T’s suite of standards for 40 Gbit/s fibre to the home
The NG-PON2 series consists of three standards: ITU-T G.989.1, G.989.2 and G.989.3.
- ITU-T G.989.1 describes the general requirements of NG-PON2 systems.
- ITU-T G.989.2 specifies characteristics of the NG-PON2 physical media dependent (PMD) layer.
- ITU-T G.989.3 specifies the NG-PON2 frame formats, messages, and protocols for data transmission.
The ITU-T standards underlying optical systems for fibre access networks are developed by experts working under the auspices of Question 2 of ITU-T Study Group 15. These experts continue to work in the interests of enhancing the data rates achieved by fibre access networks. A study of 25 Gbit/s per wavelength over PON has been initiated with the aim of enhancing the capacity of PON systems to beyond 100 Gbit/s.
More information on ITU-T Study Group 15 can be found on the group’s homepage.