After a four year gestation period typical of global communications standards, G.fast has reached the point where chipset makers can implement parts against stable specifications. Formal approval of the physical layer spec, G.9701, is expected by the end of 2014. G.9700, dealing with power spectral density issues, was approved earlier this year.
What does G.fast do? Conceptually, it is the evolution of DSL, delivering broadband over copper. It clears the way for a theoretical aggregate bandwidth of as much as 1Gbps, on standard loops of telephone-grade twisted pair wire already in place to most homes and businesses.
Like its predecessors, such as the current VDSL2, G.fast begs the question of FTTx – fiber to the cabinet (FTTC), distribution point (FTTdp), premises (FTTP), node (FTTN), or other entity close enough to the subscriber to complete a short run in existing copper. This is in contrast to fiber to the home (FTTH), which requires similar points of presence but also ripping up yards, driveways, junction boxes, garage walls, and other pieces of a dwelling to provide service. For the last 200m, G.fast can be far cheaper than FTTH, and provide substantial bandwidth.
Faster signals bring with them quality and interference challenges. G.fast is relatively short range. Compared to VDSL2 which can handle several thousand meters with some degradation, G.fast handles at most 250m, and really only performs at shorter ranges. Fortunately, most lines are shorter – BT says 80% of copper lines in the UK are less than 66m. To gain performance, G.fast ups the frequency, operating in a 106 MHz profile with a future of 212 MHz, overlapping FM bands.
With concerns in both power spectral density shaping and far-end crosstalk reduction, DSP comes into play with vectoring algorithms. In the recently announced DP3000 DPU chipset and CP1000 CPE chipset, Sckipio makes heavy use of the CEVA-XC DSP core for G.fast vectoring.
VDSL2 introduced vectoring, and G.fast takes it to a new level of effectiveness. With a wider frequency range, G.fast vectoring engines require advanced algorithms and more calculations. To keep complexity realistic, G.fast limits bit loading to 12 bits per frequency carrier, compared to 15 in VDSL2. The gains in crosstalk reduction using G.fast vectoring are massive.
Among equipment providers, Alcatel-Lucent and Huawei are both pushing G.fast. As with any advanced standard, the driving factor is integrated chipsets to provide performance and reduce costs for volume rollouts. Sckipio has the lead here with G.fast vectoring built in to their solution, with Broadcom still working on multi-chip solutions.
Will G.fast be broadly adopted? The telcos are pitted against DOCSIS 3.1 and cable operators, working a hybrid fiber coax (HFC) architecture. Some say with the need to roll fiber to the last 200m, G.fast may be simply a stop-gap to FTTH. Others say that last 200m is a 20 year project to cover an entire country, and G.fast speeds without tearing up copper are worth it.
It may be longer in the US, lagging behind in broadband with large distances to cover and lack of competition in most markets. By any measure, Akamai or the UN Broadband Commission, US broadband penetration and speed generally sucks. (The UN conclusion that WiMAX would be most cost effective is rather hilarious – in the words of Dr. McCoy: “It’s dead, Jim.”)
Alternatives complicate the picture. Broadband in the US is two-thirds cable. Google Fiber is fast but very selective with build-on-demand instead of metro-wide rollouts – effectively, you have to move to the “fiberhood” to take advantage of it. VDSL2 may represent “good enough” performance with the ability to span longer distances, especially in rural contexts.
It will likely be at least another year of trials before we see if G.fast gets wide scale traction. It seems well suited for dense urban markets in Europe and Asia even if North America is slow to adopt it for other reasons. Improved speed over VDSL2 and the appeal of consumer self-installation and quicker deployment compared to FTTH should spur uptake.Share this post via: