The International Telecommunication Union (ITU) has gained first-stage approval (“consent“) for a new set of international Fibre-to-the-Home (FTTH/P) broadband standards, which can support both 40Gbps speeds (NG-PON2) and symmetrical 10Gbps speeds (XGS-PON).
Strictly speaking ISPs can already offer similar performance over their existing ultrafast fibre optic networks and indeed we’ve recently seen Singtel in Singapore promote a 10Gbps (Gigabits per second) service using their 10GPON (Gigabit Passive Optical Network) platform (here). Back in 2012 BT also demoed 10Gbps using a similar setup (here).
However the new standards go beyond those (see below for details) and it’s always helpful to ensure that everybody is building / using kit that is created to the same specification, which ensures good general compatibility. Both of the new standards were developed by the ITU-T Study Group 15.
The previous XG-PON standard only ensured an asymmetric speed of 10Gbps download and 2.5Gbps upload, while a symmetric connection like the new XGS-PON can push 10Gbps in both directions and that’s a very significant improvement.
The new XGS-PON is said to reuse “existing PON standards to the maximum extent possible” and its physical layer follows the XG-PON (ITU-T G.987.2) and 10GE-PON (IEEE 802.3) standards. Meanwhile 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 also 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,” said the ITU without twisting its tongue in the process.
The big news today is of course the ITU’s new 40Gbps capable NG-PON2 standard, which mixes together ITU-T G.989.1, G.989.2, G.989.3 and is said to be the “first series of standards” that will provide download speeds beyond the current 10Gbps.
The main enhancements with NG-PON2 are provided by its use of multi-wavelength operation and ONU wavelength tunability in both transmitters and receivers (this reuses some of ITU-T G.988 and its wavelength management follows the guideline in ITU-T G.9802).
ITU Statement on NG-PON2
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.
Apparently major operators are already testing this new system with the “intention of deploying these systems in the near future.” Operators implementing NG-PON2 will be able 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).
Sadly the United Kingdom probably won’t be seeing 10Gbps FTTH/P broadband networks on a truly big national scale for another decade or two and even then it will take a lot of time and money to deploy, although many of the FTTH/P networks that have been built so far (around 400,000+ premises passed) could in theory be upgraded to support the new standards (not that you need or could even fully use such speeds).
It’s worth noting that the ITU are also investigating the possibility of 25Gbps per wavelength over PON and they’re doing so with the aim of enhancing the capacity to beyond 100Gbps in the future, which would bring FTTH/P services it up to the sort of standard that some core network links already deliver.
Separately there has also been a third development today (ITU-T G.709/Y.1331 – “Interfaces for the Optical Transport Network“), which saw the ITU-T grant first-stage approval of a revision to a key ITU-T standard underlying the Optical Transport Network (OTN) that will enable optical transport at rates that go higher than the current 100Gbps. This is of more use for major core network links rather than domestic FTTH/P.
The new standard extends OTN with a flexible n x 100G frame format (OTUCn), which can be used for line-side interfaces up to 25.6Tbps (Terabits per second) over the next 15-20 years. Yes.. Terabits! Apparently the initial n × 100G FlexO standard (ITU-T G.709.1) will be fully approved by the end of 2016 and standards for n × 200G and n/4 × 400G FlexO will be ready for when next-generation 200G or 400G client optical modules become available.
Suffice to say, there’s a lot of capacity left in them thar fibre optic cables.