In reply to a post by Anonymous:

I am not too technically minded compared to some on here so would this "shaping" of the profile around adsl / isdn etc frequencies make it possible for further profiles to be used (albeit with slightly less speeds than could otherwise be?) or would the reduced use of lower frequencies make this pointless for longer lines?

From what I can see, the power-shaping mask for the cabinets has been made to deliberately follow the frequency definitions of VDSL2's band plan 997, except to cut it off at 7.05MHz instead of 8.5MHz. BT's documentation say that it is impossible to mix band plans on any one set of plant, which altogether suggests that we would never see any other band plan introduced.

Could the plans be extended upward from 7.05MHz to 8.5, 12, 17 or 30MHz? There is no reason why not (the mask would need changing to suit), but I do wonder why they capped things at 7MHz when 8.5MHz was both the standard and an "easy" jump.

Extending from 7MHz to 8.5 or 12MHz would improve the bandwidth available on the upstream side. Up to 17Mhz will then improve the downstream side. Graphs I've seen suggest that the biggest improvements do come on the upstream side, eg white paper, but pretty much restricted to distances well under 1km.

I wonder if the extended profiles are really going to end up in blocks of flats, rather than out on the streets. Getting any widespread benefit from them will probably require BT to start distributing their cabinets more, getting shorter distances (FTTKerb instead).

Other than specifying the top-end frequency, the profile mainly specifies the maximum power to be used.

In reply to a post by Anonymous:

From what I have heard the BT option of 2meg uploads actually caps the sync rate not just throughput, so will the current profile (8c?) allow for greater speeds (assuming it is being capped) or is this really it until ofcom / BT agree new frequency plans?

The limit that BT are currently placing is 15Mbps, but you don't see this mentioned much - the packages most visible are 10Mbps and 2Mbps - and the 10Mbps service probably extends about 500m. I suspect the 10 and 15 Mbps services are the limit of the technology at the allowed frequencies, so any expansion will indeed need to use one of the 12MHz profiles, at least.

well i am getting strange speed tests tonight i am on bt infinity option 2
and it was not wireless

http://www.mybroadbandspeed.co.uk/results/89654361.png

Date Download Speed Upload Speed
Today 22:47 36222 kbps (4.53MB/s) 8309 kbps (1.04MB/s) Share
Today 22:31 37488 kbps (4.69MB/s) 6011 kbps (751kB/s) Share
Today 22:28 73253 kbps (9.16MB/s) 8261 kbps (1.03MB/s) Share

anyone else on bt infinity getting strange speeds ?

i am about 180 metres from the Cabnet

Edited by deleted (Thu 14-Apr-11 23:11:14)

What AV/FW system do you have?

sorry bob what is av/fw ?

AntiVirus/Firewall

Trend Micro Titanium i tried it with it on and off and still gave mthe same results

Edited by deleted (Fri 15-Apr-11 12:38:54)

Doesn't VDSL2 equipment chuck out 250Mbps at the DSLAM (If it isn't capped in any way) and if it is set to the right profile?

From Wikipedia: "VDSL2 deteriorates quickly from a theoretical maximum of 250 Mbit/s at source to 100 Mbit/s at 0.5 km (1,600 ft) and 50 Mbit/s at 1 km (3,300 ft), but degrades at a much slower rate from there, and still outperforms VDSL."

Could BT reach this speed in the future?

Edited by chris6273 (Fri 15-Apr-11 06:00:33)

The 8MHz profiles can handle 75/20 at the cabinet, and 45/15 at 500m.
The 17MHz profiles can handle 120/50 at the cabinet, and 75/30 at 500m.
The 30MHz profile can handle 140/140 at the cabinet, and 75/30 at 500m.

My suspicion is that you'll only get the 8MHz variant in today's cabinets. The higher frequencies will only come if BT start putting mini DSLAMs out on poles or in buildings, much closer to the end user. That also reduces the amount of crosstalk each line is subject to.

In reply to a post by RobertoS:

BT's plans are a complete mystery.

Even to themselves I'll wager.

DrT