Feel the noise (and silence)
Noise is reduced by a scheme called vectoring. Most consumers’ phone lines are bound together when they reach the kerb. This close proximity between wires causes “crosstalk” - where receivers on one line can hear what is being said on the other line. With digital signals this is highly problematic, as the modem needs to distinguish between signals belonging to its connection and "noise".
Vectoring, which is part of the VDSL specification, works a little bit like noise-cancelling headphones. It looks at what noise is leaking into the individual subscriber’s pair by sending a known symbol (with the receiving end looking for it) and then, using DSP code at the transmitting end, cancels out the interference. This is clearly a fantastically compute-heavy task.
In the scenario with a lot of noise the standard has a narrow channel called the Robust Management Channel, which works to fill in the missing bits and keep the data flowing; specifically, by improving the communication and reduces the frequency that links are lost by. If that fails there is rapid reconnection with a protocol called Fast Online Reconfiguration.
This restores the connection much faster than the VDSL specification, and in turn, establishes the vectoring (something VDSL 2.0 has as well) very much faster as the effect multiplies up depending on how many customers are being served.
Keep off the grass
A lot of the emphasis on G.fast is to keep installers out of people's houses. Weissman claims that even in low labour cost countries where it's economic to install fibre to the home, people so dislike the workmen digging up and relaying gardens and routing cables inside their homes that they would rather stick with what they have.
Fortunately, in the distribution point model, the bit that gets replaced with fibre is the legacy copper (which will have degraded and cause the noise), while copper inside people's homes tends to be in better condition.
Where next for Sckipio?
Sckipio will have to take on the established players with its chipsets, notably Broadcom and Ikanos, and while it makes the chips other vendors will have to pick those up to build the boards and customer equipment.
Sckipio has produced reference designs which are targeted at (mainly Chinese) OEMs but really the company needs a big win, such as Huawei, Netgear, Cisco or Alcatel. The bigger brands are favoured by the telcos who actually buy the equipment.
Sckipio has partnered with fabless chip company Lantiq to build reference boards.
It’s been said that BT has more copper in the ground than many copper mines, and G.fast will certainly add value to that. However, it’ll be really interesting to see if Sckipio can extract the value. ®