ITU-T Sets New Standards for 40 Gbps Fiber to the Home

  • ITU-T
GENEVA — ITU-T members have followed the recent approval of two new standards: 40-Gigabit-capable Passive Optical Networks (NG-PON2) and 10 Gbps Symmetric fiber to the home.

40-Gigabit-capable Passive Optical Networks (NG-PON2)

40-Gigabit-capable passive optical networks (NG-PON2) with the first-stage approval 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 fiber-optic access speeds beyond 10 Gbps.

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 Gbps in each direction. Each wavelength is capable of providing a subscriber with optical access up to a rate of 10 Gbps, and the upstream/downstream wavelength is also capable of operating at the lower rate of 2.5 Gbps. 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); radio frequency 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.

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 fiber 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 Gbps per wavelength over PON has been initiated with the aim of enhancing the capacity of PON systems to beyond 100 Gbps.

10 Gbps Symmetric Fiber to the Home
ITU-T members have achieved first-stage approval of a new international standard for optical access at the rate of 10 Gbps both downstream and upstream. The new standard will be particularly beneficial to operators as a cost-effective means of upgrading the capacity of the connections provided to businesses in need of symmetrical service.

XGS-PON offers a point-to-multipoint optical access system to support a wide range of broadband and narrowband services to homes and businesses, as well as mobile backhaul and other applications.

XGS-PON reuses existing PON standards to the maximum extent possible and capitalizes on PON development efforts underway in the industry. The physical layer of XGS-PON follows XG-PON (ITU-T G.987.2) and 10GE-PON (IEEE Standard 802.3). The standard fully supports operators’ use of existing 10 Gbps symmetric transceiver components. The design of the XGS-PON protocol layer is based on NG-PON2 (ITU-T G.989.3) and XG-PON (ITU-T G.987.3), and its ONU management and control mechanism is specified in ITU-T G.988.

XGS-PON operates on the same optical distribution network (ODN) as XG-PON. The typical distance between the optical line terminal (OLT) and an optical network unit (ONU) is 20 km, and one OLT is capable of supporting up to 128 ONUs. The XGS-PON wavelength plan provides for co-existence with G-PON, XG-PON and NG-PON2. An XGS-PON system is fully backward compatible with XG-PON ONUs, allowing the operation of both XGS-PON and XG-PON ONUs under a single XGS-PON OLT port.

The ITU-T family of 10 Gbps PON standards now offers both asymmetric and symmetric transmission for broadband services, with XG-PON enabling downstream service at 10 Gbps and upstream service at 2.5 Gbps, and XGS-PON enabling 10 Gbps bi-directional service.

The ITU-T standards underlying optical systems for fiber 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 fiber access networks. A study of 25 Gbps per wavelength over PON has been initiated with the aim of enhancing the capacity of PON systems to beyond 100 Gbps.

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