50G PON Takes A Step Closer to Reality as ITU-T Standard Achieves Consent
Updated: May 8, 2021
The ITU-T 50G PON standard took a big step towards become a reality as consent was achieved on multiple part of the series during the ITU-T SG15 plenary meeting on April 23, 2021.
ITU-T Study Group 15/Q2 launched the Higher Speed (HSP) PON project in 2016 which was completed and released in February 2018 as ITU-T G.Sup.64. This supplement described the characteristics of optical transmission above 10 Gbps per wavelength between the optical line termination (OLT) and the optical network unit (ONU) and will be applied towards all PON standards above 10G PON.
The 50G PON Standard, G.9804 (also referred to as HSP – Higher Speed PON) is currently comprised of the following series:
G.9804.1 - Higher Speed Passive Optical Networks: Requirements – consent (July 2019), approval (November 2019)
G.9804.1 Amd.1 - HSP - Amendment 1- consent (April 2021)
G.9804.2 - Higher Speed Passive Optical Networks: Common Transmission Convergence Layer Specification – consent (April 2021)
G.9804.3 (G.hsp.50Gpmd) – Physical Medium Dependent Layer for 50G single Channel PON systems – consent (April 2021)
G.hsp.TWDMpmd – Higher Speed Passive Optical Networks: TWDM PMD - understudy
50G PON offers Smooth Evolution Path
With mass deployment of GPON between 2010-2020 and 10G PON from 2020-forward, the need to share requirements with existing systems has been a key characteristic in the development of the 50G PON standard. This means that all HSP systems must operate over a legacy power splitting-based optical distribution network (ODN).
The ability to reuse the existing investment in the optical distribution network is highly attractive to operators – especially when it accounts for a significant portion of the total investments in FTTH networks. Additionally, the ability to reuse the ODN allows for an “ease in migration” rather than a forklift upgrade.
In the Global Service Provider Surveys on 10G PON Deployment Strategies conducted by Broadbandtrends over the past 3 years – coexistence and migration from existing network to new network has been a top concern for the majority of operators in addition to cost concerns, while the ability to reuse the existing ODN has been a top driver.
In short, any new PON standards must support the requirement for ease in network evolution. Specifically, it must support the coexistence of legacy PON systems and HSP systems in the same fiber infrastructure (ODN), while minimizing service interruption of ONUs during evolution and upgrade
Currently deployed PON systems include: GPON, EPON (1G), XG-PON1, XGS-PON, 10G-EPON and NG-PON2. As such, the HSP systems should be able to support operation on the legacy PON ODN infrastructure.
In ITU-T G.9804.1, three generations of PON system coexistence are described offering various upgrade paths, supporting legacy PON generations, such as GPON, XG-PON, XGS-PON, and 10G EPON, to evolve to higher system capabilities.
There are two main methods to achieve PON evolution and upgrade (which have been specified in ITU-T G.9804.1) include (1) by external coexistence elements (CEx) and (2) multi- PON module (MPM) – also referred to as combo-PON card or universal PON card.
The MPM method has certain technical and cost advantages over the external coexistence element option. Its main attraction is offering a simplified deployment method, where operators can simply replace the previous PON OLT line card with a new generation OLT line card, without the need to add/replace existing chassis or perform fiber rearrangement. This reduces engineering planning as well as equipment costs associated with the deployment of a CEx.
The downstream wavelength of 50G TDM PON has been agreed to be 1340– 1344 nm. While the upstream wavelength of 50G TDM PON has been allocated multiple options. This is to allow for the different coexistence requirements of operators globally. At present only support for upstream of 10Gbps and 25Gbps is agreed.
Although it is expected that the majority of operators will be looking for coexistence of 10G PON with 50G PON, it is not unforeseen that in some markets, GPON coexistence may still be necessary. As such the following wavelength plans have been agreed:
Option 1: for coexisting with XG(S)-PON/10G EPON using WDM: wideband, 1290~1310 nm; narrowband, 1298~1302 nm;
Option 2: for coexisting with GPON supporting both narrowband (1300–1320 nm) and reduced (1290–1330 nm) upstream wavelength options: wideband, 1260-1280 nm.
10G PON to Be Defacto Standard Until 50G PON
The industry is currently at the beginning stages of upgrading from GPON to 10G PON, which is expected to last the next 3-8 years. However, given the rate of increase in bandwidth demand and the increasing number of applications that will require faster speeds, it is not an unlikely scenario that 5Gb or 10Gb broadband services will become standard products. As such, the need for higher speed PON systems will be necessary.
The G.9804.x series of standards has been defined to enable an simplified upgrade path for operators that will offer a flexible architecture supporting multiple upstream and downstream rate access, flexible latency control and other capabilities on one single PON infrastructure for residential, enterprises, wireless network and more to offer new opportunities for future optical access networks.
ITU-T G.9804.1 - Higher Speed Passive Optical Networks: Requirements includes overall system requirements, evolution and coexistence, and supported services and interfaces of high-speed PON systems. The standard achieved consent in July 2019 and was officially approved in November 2019. Amendment 1 to Recommendation ITU-T G.9804.1 includes additional requirements for higher speed PON with consent achieved in April 2021.
ITU-T G.9804.2 defines a converged transmission convergence layer for use in all high speed PON systems. This TC layer will have support for a wide range of PMD types, including single and multiple channels, fixed and tunable wavelengths, a range of speeds, low latency and channel bonding capabilities. This standard achieved consent in April 2021.
G.9804.3 (G.hsp.50Gpmd), provides the specifications of the physical medium dependent (PMD) layer for 50G single channel PON systems. This includes the ODN characteristics, the wavelength plan, the power budget, and interfacing to the common transmission convergence layer. Consideration will be given to compatibility and technology reuse between this system and multichannel systems. This standard remains under study.
ITU-T G.hsp.TWDMPMD, Higher Speed Passive Optical Networks: TWDM PMD includes 50 Gbps TWDM PON physical layer architecture, optical layer interface parameters, etc. This is in the early stages of development.