G.Fast Delivers Gigabit Broadband Speeds To Customers Over Copper (FTTdp)

Subject: General Tech | August 5, 2013 - 07:10 AM |
Tagged: rf, itu, gigabit broadband, fttdp, fiber, broadband, bell labs, alcatel lucent

Alcatel Lucent has been working on a new broadband technology called G.Fast that is currently undergoing ITU (International Telecommunications Union) scrutiny and may be ready to implement as soon as 2015. G.Fast is a technology that builds upon VDLS2 and is the next step between the currently-popular FTTN (Fiber To The Node) and true fiber FTTH (Fiber To The Home) internet services. Alcatel Lucent’s G.Fast technology is rated for speeds up to symmetrical 1 Gbps over copper lines up to 200 meters and 500 Mbps at up to 300 meters.

G.Fast is currently being tested by Telecom Austria and is being evaluated as a standard by the ITU. G.Fast requires fiber to be pulled closer to consumers, but avoids the massive expense of doing true fiber runs to each individual home. Unlike traditional DSL which is served from a central office up to miles away, or newer VDSL technology like AT&T's U-Verse service that is served from a DSLAM that is located about a mile from customers, G.Fast serves customers from a fiber distribution point that is a maximum of 300 meters away from customers. In the latter two cases, the internet connection is fiber up to the DSLAM or distribution point after which it uses the existing copper phone lines to reach customers' homes. The G.Fast distribution point is about the size of a large shoebox and can be mounted on telephone poles or underground.

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G.Fast implements pair bonding, vectoring, and phantom mode techniques (more information, PDF) in addition to a physically closer fiber connection (internet speeds drop off dramatically as copper cable length increases due to cross talk on the cables, interferrence from other RF sources, and other factors). Specifically, G.Fast is able to use multiple physcal copper pairs (pair bonding) along with multiple virtual pairs per each physical pair (phantom mode), and an active noise monitoring and cancelling system to reduce cross talk and interferrence (vectoring). Additionally, G.Fast uses a surprising 100Mhz of spectrum over the copper pair(s) and fancy modulation techniques to wring all the speed possible out of existing telephone lines. For comparison, traditional old-school DSL that you would get from your local telephone provider uses less than a MHz of spectrum, and the latest VDSL2 technologies use around 1MHz of RF spectrum! There is an interesting problem with G.Fast beyond punching all this through the cables, and that is possible issues with FM broadcasters (radio stations) that use RF spectrum between 87.5MHz and 108Mhz. The Register notes that ISPs that implement G.Fast will have to work around the specific FM frequencies actually used in the local area to avoid interferrence. That suggests that operators may not be able to use the full 100MHz of spectrum in the standard, but it would still be a huge step up from VDSL. The site further explains that even if the copper lines are buried underground, it could still cause issues with FM broadcasts as the 200-300 meter line makes for a massive antenna.

Another point in favor fo G.Fast is that it is designed to be a customer installed technology in the sense that customers will be able to plug in their modems to the standard phone jack and recieve service. (Ideally, this would mean no need for technicans to do so-called "home runs" to get the best speeds, but if it is needed with U-Verse it may still be needed for G.Fast, especially in older apartment buildings.)

The ITU is currently looking at G.Fast and working towards a standard along with developer Alcatel Lucent and various telecoms interested in implementing the technology. According to Frank van der Putten of the ITU, G.Fast could be approved as soon as early 2014 with hardware supporting it available in 2015.

G.Fast is by no means the end-all-be-all of internet connections for home users, but it is a massive performance leap ahead of current DSL technologies and thanks to competition from Verizon FIOS, Google Fiber, local municipalities building out their own fiber neworks, and cable companies (in the US at least, where internet over coax is common), G.Fast may be economical enough that telecos are willing to upgrade their networks to head off these competitors all while moving their true fiber networks all that much closer to people's homes and to the (hopefully/ideal) eventual implementation, and final upgrade to, Fiber to the Home connections.