Dark Blue: Firm commitments from incumbent: BT (10M), Belgacom, Australian NBN, Swisscom, Austria, Bezeq Israel, Chunghwa Taiwan, Telus Canada, Telekom South Africa, SK Korea, (U.S.) AT&T, Century, Frontier, Windstream, Belgium, Omantel
Mid Blue: Smaller carriers in Germany, Norway, Finland, Japan
- Published: 09 October 2014 09 October 2014
200-600 meg pretty fast so why hype? British Telecom, despite the BBC and other news reports, did not attain a gigabit with G.fast. They merely showed that 104 MHz over a protected standard copper line could reach speeds of 786 megabits down 19 meters, something obvious for years from the basic engineering. The substance of G.fast is significant so the hype is unneeded.
BT's results were not for G.fast. G.fast is a 300 page specification that BT/Huawei didn't even pretend to support. Many features, such as reverse power, are important and were not implemented. Vectoring in G.fast remains totally unproven and will be crucial to any deployment. Several features of G.fast are likely to reduce the speed. The effect may be relatively modest but we won't know until they are tested.
Real deployments will probably have to notch out some of the bandwidth, reducing speeds. Interference with terrestrial radio and possibly other things will require not using the full spectrum.
BT's deployment of G.fast will likely be 20-40% slower because they will have to protect their existing VDSL. Most G.fast deployment plans will have to forfeit the first 21 MHZ or so to protect the existing VDSL service. BT has VDSL to 82%, according to their press release below, one of the widest VDSL deployments in the world. It would be amazing if they turned all that off and wasted the investment anytime soon. I believe BT is only using 17 MHz for VDSL; VDSL goes to 30 MHz and would therefore require sequestering even more.
Broadband speeds are almost always measured in one direction but BT is adding upstream and downstream to get to the "Gigabit" headline. G.fast is time domain, meaning you can switch the ratio between upstream and downstream in software. But you can't go all the way to 100%, which would not merely prevent upstream use but would block the acknowledgement packets required for the Internet. I believe adding the two directions to get a headline began with chipmakers, who called three year old 100 down, 100 up VDSL "200 megabits" and presented a "breakthru. I heard it first from Broadcom but I don't know if they originated the meme.
Adtran put out a press release on a related technology that combines VDSL and G.fast but I choose not to report it because they didn't have even lab results. Adtran is doing much better in Europe than expected two years ago, taking part in BT's coming trials and winning at least some ports in Deutsche Telekom.
The BBC reports "BT said commercial equipment could be available from manufacturers by December 2015." That a useful perspective because several chip vendors have been suggesting revenue from an earlier date. More realistic is that next spring's G.fast conference in Paris will show progress and problems continuing. See you there, I hope.
Thinkbroadband.com and Telecompaper avoided the gigabit spin but most of the mainstream media picked up the story as BT promoted it.