The International Telecommunication Union, specifically ITU-T Study Group 15, has doubled the best speeds achievable via the new G.fast broadband standard to 2Gbps and added support for coaxial cable. Openreach (BT) are due to begin the commercial UK roll-out of this service in late 2017.
Under the current plan BTOpenreach’s G.fast (ITU G.9700/9701) technology should deliver around 300Mbps (50Mbps) over 300-350 metres of traditional copper line and they intend to make this service, which will be predominantly deployed from extension pods on the side of existing PCP street cabinets, available to 10 million UK premises by 2020 (rising to “most of the UK” by 2025).
At present the G.fast implementation being used by Openreach (see the technical details) is based on the first official standard and as such it will harness up to 106MHz of spectrum frequency (the ‘up to’ 80Mbps capable FTTC / VDSL2 service only needs around 17MHz), which at best could deliver a top speed of 1000Mbps on a very short copper line (less than 50 metres).
However the latest amendments to the ITU’s G.fast standard will allow the full 212MHz to be used, although you’d have to live very close to the local distribution point in order to expect 2000Mbps and in any case Openreach currently has no plans to offer that sort of speed.
The ITU has also enabled G.fast to be used over coaxial copper cables (Virgin Media use these and so do some big buildings) and the wider changes also involved a transmit power tweak (we believe up to +8dBm).
The third amendment of ITU-T G.9701 doubles the aggregate net data rate achievable with G.fast, increasing its capacity to 2Gbit/s using spectrum up to 212 MHz. The update to the standard maintains spectral compatibility with VDSL2. The coexistence of G.fast and VDSL2 offers service providers the agility required to switch customers between G.fast and VDSL2 as business operations demand.
The amendment extends G.fast’s application to coaxial cable, enabling the coexistence of G.fast and satellite signals in coaxial cable infrastructure. The amendment also specifies a mechanism for dynamic time assessment, functionality that enables upstream or downstream transmission to exploit G.fast’s full aggregate net data rate. This functionality will improve users’ broadband experience by increasing upload or download speeds in line with the demands of the applications in use.
The refined standard(s) has already achieved first-stage approval (“consent“) and is expected to see final approval before the end of 2016, which is just in time for Openreach’s pilot. The operator intends to grow their G.fast pilot to 17 UK locations from January 2017, reaching around 138,000 UK premises by the end of March 2017 (here). Initially the service will offer top download speeds of ‘up to’ 330Mbps (50Mbps upload), with a lower tier of 160Mbps (30Mbps upload).
BT believes that it’s theoretically possible to deliver 300Mbps over a 350 metre copper line using G.fast (most other operators are targeting sub-250 metres), although the outcome of their recent trials suggested that more work was needed (here). It will be interesting to see whether the latest developments are able to deliver on that promise, which is important if BT’s fibre-light approach of using existing cabinets is to work its full magic (as opposed to a more expensive a fibre-rich FTTdp deployment).
One thing that would surely turn a lot of consumers off is another round of FTTC style speed variability, which to some extent is inevitable (i.e. advertising top speeds of 300Mbps, but only being able to deliver considerably less to many premises). On the other hand most people would still be happy with less than 300Mbps, although it would be nice if BT could stay in 100Mbps+ territory for all of its G.fast enabled lines.
Elsewhere the ITU has completed new standards detailing commonalities in software-defined networking (SDN) and automatically switched optical networks (ASON). On top of that some revisions to ITU-T G.652 and G.657 have extended and optimized the use of optical fibres beyond their current capabilities.
Finally ITU-T G.654, which traditionally dealt with the characteristics of fibres for submarine cables, has been revised to include a new subcategory of fibre (G.654.E fibre) to support coherent digital transmission systems in terrestrial optical networks at rates beyond 100 Gbit/s.