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gfast map June 2017

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

Light blue: Smaller carriers" Germany, Norway, Finland, Japan

Green: Incumbent likely: Belgium, France, Germany, & Poland  Country by country details. 

35b tones200 megabits+, old modems still work. G.fast is headed over a gigabit on short loops  35b was introduced in 2014 as a simple, fast, low cost upgrade that could more than double speeds on existing VDSL lines. It uses 35 MHz of spectrum rather than the 17 MHz of most European VDSL builds but otherwise is nearly the same. Chipmakers - several now out of business - promised chips ready to deploy by 2016. 

Simulations suggested 35b speeds could go up to 350 megabits over short distances. Adtran shared with me test results showing 200-250 megabits+. Alcatel/Nokia had similar results. Both were very confident a year ago. Until DT commented it would be 2018, that seemed reasonable to me. 

In the picture, the green middle row is 17 MHz VDSL, deployed by the millions in Germany and elsewhere. Above that, in red, is G.fast. You can see the G.fast tones are wider than the VDSL. That makes it impractical to do effective noise canceling (vectoring) between the two systems. Unvectored VDSL typically runs at about half the speed.

On the other hand, 35b, the blue line beneath, uses the same tone spacing as the 17 MHz. In theory, that meant they could work well when lines share the binder. Apparently, no one understood the problem. Deutsche Telekom recently said 35b would not be deployed until 2018. Everyone's mum about the cause, but DSLAM vendor Adtran confirms the delay.

Several telcos are enthusiastic because it means they don't have to upgrade their existing customers. Deutsche Telekom is enthusiastic about 35b because they don't want to spend the money upgrading the older modems.

There's an excellent introduction to G.fast by Keith Russell, Paul Spruyt, and Stefaan Vanhastel of Alcatel, now Nokia, from 2014 that remains on target today. The illustration is from that article. Two things have developed since. G.fast has improved the performance at 250-350 meters, to roughly match 35b. In addition, Sckipio believes the 350-500 meter performance of G.fast could be similar to 35b under similar conditions. All this remains to be proven by field tests.  

 
 

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