BT to roll-out superfast broadband to 40% of UK by 2012

BT has announced that it plans to roll-out superfast broadband to 10 million households by 2012 at a cost of £1.5 billion, which will provide broadband connection speeds of up to 100 Mbps. BT plans to use a combination of FTTH (fibre-to-the-home) and FTTC (fibre-to-the-cabinet) to deliver superfast broadband, which are described below.

As its name suggests, FTTH refers to fibre optic cable going all the way from BT's network into people's homes. FTTH will allow broadband connection speeds of 100 Mbps, and BT said that it's possible for this to go up to 1,000 Mbps in future, which is because fibre optic cable can handle effectively any amount of bandwidth that broadband users could throw at it.

FTTH is a lot more expensive to roll out than FTTC in the UK, though, because it requires roads to be dug up to lay the fibre optic cable all the way to homes and business premises. BT has said that it will use FTTH for new-build housing developments and for locations where it's economically viable to do so, which will likely consist of locations such as blocks of flats, because of the high number of households that could be covered in one fell swoop.

FTTH is widely used in South East Asian countries which is due to the fact that a high percentage of peoplein those countries live in blocks of flats. But FTTH is likely to only account for a small minority of all the superfast broadband household coverage BT will provide in the UK, though, because of the far smaller percentage of people that live in blocks of flats.

FTTC will probably be the way that the large majority of households will get superfast broadband from BT by 2012, and BT said that this method will initially deliver speeds of up to 40 Mbps, but BT is working on technologies that could increase this up to 60 Mbps (see below for more details on this).

FTTC consists of fibre-optic cable being laid from BT's telephone exchanges to the roadside telecoms cabinets (so it still requires roads to be dug up, but it will just require less digging than would be needed for FTTH), and from there onwards VDSL2 will be used to carry the data over the final stretch of copper telephone wire that people already receive their ADSL signals on.

The reason FTTC is set up like this can be explained by referring to the figure below which shows VDSL2's theorectical download speed versus loop length, which is the length of the copper wire that the VDSL2 signal has to travel over. All of the DSL variants suffer from the same problem that the download speed drops the longer the loop length is, because the longer the signal has to travel over the copper wire the more the signal strength drops, and this reduces the all-important signal-to-noise ratio (SNR) level at the DSL receiver, which is what determines the maximum transmission speed. With FTTC, fibre is laid from the local telephone exchanges to the roadside telecoms cabinets, which are closer to people's homes, and this reduces the loop length so that the download speeds will be higher.

VDSL2 also provides upload speeds that are comparable to download speeds, which offers a massive improvement compared to ADSL, which provides far higher download speeds than upload speeds — the 'A' in ADSL stands for 'asymmetric' due to the asymmetry between the download and upload speeds. Higher upload speeds would benefit online gamers and file-sharers on P2P networks.

BT said that they will consider rolling out superfast broadband to areas that don't get it by 2012 depending on how much demand there is for it from consumers. BT added that ADSL2+ with speeds of up to 24 Mbps will be nationally available by then because all of BT's telephone exchanges will have migrated to its new 21CN (21st Century Network) by 2011 anyway, and all of the exchanges will support ADSL2+. BT said that "the majority" of ADSL2+ users would see speeds of 10 Mbps.

BT says that it will roll out superfast broadband to both urban and rural areas, although given that rolling out superfast broadband nationally is estimated to cost in the region of £15 billion, and BT is only planning on spending £1.5 billion to cover 40% of the population, it's very likely that BT will try and cover areas with the highest population density, and people out in the sticks are unlikely to get it.

In BT's press release, they also mentioned that they've reduced their charges to other ISPs who pay BT for transporting data over BT's network:

Are you taking action to reduce the congestion caused by services such as the BBC’s iPlayer?

Yes. BT has made it much cheaper for companies to buy extra capacity on the “backhaul” pipes that link exchanges to the core network. This move should ensure Internet congestion is minimised. BT will also invest significant funds in improving core network capacity.

BT still operates over 60% of all broadband lines in the UK, and the LLU (local-loop unbundling) ISPs pay BT to deliver data to their users who're on telephone exchanges that the ISPs haven't unbundled yet. The recent issue where the ISPs were moaning about the amount of bandwidth that the BBC iPlayer was generating was was totally down to the high — some ISPs would say extortionate — cost of BT's "capacity-based charging", where BT charges the ISPs for the amount of data it delivers to the ISPs' subscribers on their behalf. The issue over the iPlayer bandwidth was never about there being any limitations in the underlying technologies that transport data around the Internet, because advances in fibre-optics technologies are far outstripping increases in demand for Internet bandwidth. For example, 1 gigabit Ethernet is typically used by ISPs to transport data on the 'backhaul', but there's a 10 Gbps Ethernet standard that's getting cheaper to use as more businesses start using it, and there are 40 and 100 Gbps Ethernet standards in the pipeline.

So with BT making extra capacity "much cheaper", presumably we won't hear the ISPs moaning about the iPlayer bandwidth any more. It's a shame that BT reducing their charges, and hence sorting out the iPlayer bandwidth issue, hasn't been reported by the press (or at least it hasn't to my knowledge), but it shows that the press is only really interested in reporting on the "Internet to grind to a halt" kind of scare stories rather than reporting on this issue in an even-handed manner.

The technologies that BT is very likely to be investigating to increase the 40 Mbps top download speeds for FTTC up to 60 Mbps are called vectoring and dynamic spectrum management (DSM), which are described here. Dynamic spectrum management will consist of the signal's spectrum being dynamically altered to make best use of the spectrum — for example, higher bit rates will be allocated to frequency bands where the level of noise and interference is lower, and vice versa.

Vectoring uses similar concepts to those used on MIMO antenna arrays on mobile phone systems (and the Wi-Fi 802.11n standard uses MIMO, because equipment has two antennas), where interference is jointly cancelled to improve SNR, and this performs better than attempting to cancel interference on a line-by-line basis.

BT to roll-out superfast broadband to 40% of UK by 2012

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