BT have three possibilities with the current FTTC rollout, none of which they can do yet:
- Use up to 30MHz frequencies, instead of the current limit of 17MHz.
This is feasible today, but needs to be agreed by a standards committee (part of Ofcom). However, they've only just gone from 8MHz to 17MHz (going to 40/10 to 80/20), so there will probably be a while of lab checks & trials before they get the go-ahead for this.
This will only benefit the houses close to the cabinet (say, within 300-400 metres or so).
- Add the G.Vector standard.
The main limitations of speed in FTTC come from crosstalk between the various subscribers, whose signals are all interfering with each other. G.Vector is an additional standard that allows the cabinets to "undo" this interference with some very clever firmware.
This feature gets speeds of almost everyone back to the theoretical best for the line distance, and makes it likely that BT could offer speeds of 100-120 Mbps at peak, and retain that within 400-500 metres.
Those are 17 MHz speeds, so adding both features may make even higher speeds available.
This is standardised, and chip companies are currently ironing out compatability issues with their implementations. See
this TBB news report.
- Add bonding.
This makes use of multiple pairs in parallel.
I've seen Ericsson report speeds of 500Mbps using this, and just seen a comment that Alcatel are getting up to 1Gbps (vectored & bonded). It is still a manufacturer-led area, which I don't think has been standardised.
This relies on having spare copper out in the streets. Many houses have 2 pairs coming in from the nearest DP, but perhaps not all the way from the cabinet. It is more likely to be done on a needs-only basis for a few businesses - and even then, FTTP-on-demand might be a better solution for them.
Where will all this eventually lead? I suspect (by nothing more knowledgable than sticking my finger in the air) that speeds of 100-120 will be fairly common. 150+ will be rare.
The EU has a target, for 2020, that 50% of people will be able to get 100Mbps if they choose. It is plausible that FTTC alone could support that, and the option to get FTTP-on-demand when you're in an FTTC area will guarantee it anyway.