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G.fast: 1 Gigabit per second DSL

DSL, slow old DSL, may yet come back to compete with cable and fibre for the last-mile internet speed championship.

I used to use DSL. It was great in its day, but 6Mbps per second just doesn't cut it these days. So, I turned to cable, where I'm currently enjoying 100Mbps, and dream of Google Fibre's 1 Gigabit per second (Gbps) speeds. However, a new DSL technology, G.fast, may bring old phone lines back into the internet speed race with 1Gbps speeds — even as much as 10Gbps.

G.fast will be competitive with fibre's last-mile internet speeds.


The 1Gbps on copper technology is on its way to becoming a standard. Though there were hopes it would be finalized by now, it now looks like it won't be finished until late this year.

The sponsoring organization, the International Telecommunication Union (ITU), claims that G.fast "combines the best aspects of fibre and ADSL2." By this, the ITU means that consumers will be able to buy a G.fast modem, attach it to their land-line phone connection, and, presto, they'll get 1Gbps speeds. With this kind of speed you'll be ready to watch 4K video.

Today with VDSL2, DSL tops out, practically speaking, at 100Mbps. Far slower speeds are much more common. As the FCC observed in its 2014 report on Consumer Wireline Broadband Performance in the US, "ISPs using DSL technology show little or no improvement in maximum speeds."

This is because, the report says, "DSL, unlike cable and fiber technologies, is strongly dependent upon the length of the copper wire (or "loop") from the residence to the service provider's terminating electronic equipment, such that obtaining higher data speeds would require companies to make significant capital investments across a market area to shorten the copper loops."

Well, that's not going to happen. Indeed some companies, such as Verizon, have been accused of letting its copper network fall into disrepair. If G.fast takes off, those old copper telephone lines will become valuable property again.

G.fast drastically increases speed over copper by using wider frequency profiles than earlier versions of DSL. While VDSL2 uses 17 or 30MHz, G.fast will work on 106MHz and eventually at 212MHz.

To operate at these speeds and bandwidths, crosstalk — interference between adjacent wires — would be a real problem. To take care of it, G.fast uses vector processing to constantly monitor the wire's noise conditions and create an anti-noise signal to cancel it out in a manner similar to the way noise-canceling headphones work.

Still, G.fast isn't a perfect, drop-in replacement for traditional DSL. Its chief problem is it's only capable of delivering 1Gbps to no more than 100 meters. It's being designed to work at up to 250 meters, but it will be slower: 500Mbps. While G.fast is u nlikely to bring 1Gbps to rural areas, it would still work in suburban and urban environments.

Many telecomm equipment vendors, such as Alcatel-Lucent and Huawei are already working on G.fast silicon and modems. The telephone carriers, however, are moving slower. In Europe, Swisscom, Telekom Austria, and German Telekom are testing the technology. AT&T, which has retained its copper network, is believed to be interested in deploying G.fast.

At this time, it appears that G.fast will start being deployed in late 2015 or early 2016. The DSL-based ISPs may want to push that schedule up. Consumer and business want Google Fibre speeds and with the recent approval of DOCSIS 3.1, cable will also soon be able to deploy speeds of 1Gbps and above to home and office.

One way or the other – G.fast, fibre, or DOCSIS 3.1 – we're getting closer to the Federal Communications Commission's (FCC) dream of gigabit internet speeds being available in all US states by 2015. If the DSL-based ISPs want to be part of the conversation, they'll need to move forward with G.fast as quickly as possible.

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