BTInfinity 'upto' 40Mbps. What speed can we really expect?'

So is BTInfinity/FTTC (Fibre to the Cabinet) a viable practical technology for rural Communities?

Well it really depends on how close you are to the newly laid fibre optic and the new roadside cabinet containing newly installed DSLAMs (the bit that converts the fibre into a copper connection to your premises)

Live over 1km (as the crow flies) from your roadside cabinet (1.5km by cable) - There is not much chance of BTInfinity.

It really does depend on how many new cabinets containing fibre (in addition to the existing ones) are actually deployed 'next to where you live'. The roadside cabinet is what is important here - the nearer the better.

The technology used by BT for BTInfinity is FTTC (Fibre to the cabinet) The technology implemented (modem protocols etc), is VDSL2, this is a copper based technology, like ADSL and ADSL2+. Its copper based? - YES. BT utilise this between the Premises/Home and Cabinet.

Existing ADSL2+ is limited to speeds of approximately 24Mbps and 2.2Mbps, downstream and upstream, respectively. ADSL/ADSL2+ beyond 3.5Km are approx the same in terms of speed - upto 5Mbps, downstream. Therefore ADSL2+ would not provide much improvement outside this distance, ie. beyond 3.5km from the exchange.

VDSL2 can provide theoretical speeds of 100Mbps over copper, both downstream and upstream within 300m from the cabinet containing the backhaul fibre (the technology is also better able to cope with poor lines and offers a more stable connection speed, as it can adapt to line fluctuations better than ADSL).

Note the distance: 300m though- very close to the cabinet, the maximum is 1.5km, it drops off quickly - from 100Mbps theoretical max to 10Mbps at 2km from the cabinet. ADSL2+ is 10Mbps at 2km from the exchange. BT therefore realistically quote upto 40Mbps, because the chance of higher is very slim.

The Roadside Cabinet: The fibre optic cable deployment (FTTC) is extended from the exchange to the cabinet, and the DSLAMs are fitted in the cabinet rather than the exchange, so its a similar technology to ADSL - just where the kit is placed and a better, copper transmitting technology to deliver the final part of the signal, with significantly better upload speeds.

VDSL2 appears to be backwards compatible with ADSL/ADSL2+, whether that is implemented by BT - unsure, but if they did, ADSL2+ seems to be 15% more efficient using this VDSL2 protocol to the roadside cabinet. Whether this is due to the shorter distance because its to the cab, and not the exchange - unsure.

Data rates in excess of 25 Mbps are available for distances up to 1.2Km (by cable) from cabinet, but tail off quickly after this, minimum guaranteed deployment BT offer is 'upto' 15Mpbs/1.5km from the cabinet, below this speed BT don't deploy BTInfinity. Aluminum Cabling as opposed to Copper will affect things a lot too.

In this case, existing technologies will be deployed instead like ADSL2+ and might actually work as well at this distance as VDSL In terms of download speed (10Mbps) you receive, (not what you can upload) and are improved because we're talking distance to the roadside cabinet, not back to your exchange.

To summarise - BTInfinity's potential is looking at between 'upto' 15Mbps (distance 1.5km from cab) and a max of 'upto' 50Mbps (distance-300 metres from the cab), beyond 1.5km from the cabinet- ADSL2+/ADSL will still be deployed.

Problem is FTTC/VDSL2 - beyond 2km, from the cabinet the download speed is similar to ADSL2+ from the exchange - upto 10Mbps. ADSL, ADSL2+ are pretty much identical after 3.5km from the exchange - upto 5Mbps.

I've also read that where speeds likely to be obtained are less than 15Mbps, BT won't accept an FTTC order on that line (approx 1.5km) from the cabinet - so this maybe the current physical limit to its deployment, but might have been imposed to prevent you paying extra for something you couldn't receive in terms of service.

The technology is potentially, capable of faster speeds than the up to 40Mbps (Advertised by BTInfinity)- near to the cabinet (within 300m) but as always its very dependent on distance from the cabinet and realistically 40Mbps-50Mbps is the max. Its the same method BT describe ADSL2+ as an upto 20Mbps technology, though some users could get higher very close to the exchange (upto 24Mbps)

It really depends on how BTOpenreach deploy things - ie. If more roadside cabinets containing fibre are installed nearer to Villages outside the town containing the exchange, then it might be worthwhile method of delivering High Speed Broadband.

If BTOpenreach keep the infrastructure the same, then it is not that good for areas outside the town away the exchange/roadside cab itself - areas more than 1.5km from the roadside cabinet - these will be the new BTInfinity NOTSPOTs.