do these graphs show sudden drop offs, when the frequencies above the power back off run out? thats what I would expect. I suspect 10mbit would be about right if there was no power backoff on the adsl frequencies, it would seem the estimate took no account of that.

BTO say nothing wrong with the line,

Back to adsl2 I guess

I'm confused, I thought VDSL2 was supposed to work just as well as ADSL2 at the same distances?

Is this perhaps a profile issue? Surely 8b would make more sense for such a long line than 17a.

In reply to a post by alexatkin:

Is this perhaps a profile issue? Surely 8b would make more sense for such a long line than 17a.

Presuming you were referring to the original 8c profile, I did seem to achieve higher speeds on my "up to" 1000m line.

Using 8c, all the 40Mb DS speed was crammed in below tone 1627 (around 7 MHz):-

Discovery Phase (Initial) Band Plan
US: (0,95) (696,1183)
DS: (32,687) (1192,1627)

With 17a it's spread out over higher frequency tones (around 8.5 MHz):-

Discovery Phase (Initial) Band Plan
US: (0,95) (868,1207) (1972,2783)
DS: (32,859) (1216,1963) (2792,3959)

My connection stops bitloading at around tone 1750 leaving some DS speed "missing".
I could use all the way up to tone 1627 on my 8c profile & achieved up to 35Mb sync speed.

These days using 17a, I'm lucky if I can achieve 27Mb to 30Mb sync speed.
So, yes. The 8c profile did seem better suited to longer lines that simply can't use the higher frequency tones.

The band plan tones mentioned above are from a Huawei DSLAM.
They are slightly different from an ECI DSLAM.


We can see the original poster is connected to an ECI DSLAM & due to high attenuation over the mile long connection can only use the lowest DS band plan tones.

I have however seen users achieve up to around 10Mb on that sort of distance on their FTTC connections, again only using the lowest frequency band plan tones:-

Max: Upstream rate = 558 Kbps, Downstream rate = 8568 Kbps
Path: 0, Upstream rate = 542 Kbps, Downstream rate = 9627 Kbps

Discovery Phase (Initial) Band Plan
US: (0,95) (880,1195) (1984,2771)
DS: (32,859) (1216,1959) (2792,4083)
Medley Phase (Final) Band Plan
US: (0,95)
DS: (32,859)

Edited by deleted (Sun 27-Jan-13 22:28:49)

It just seems puzzling to use the 17a profile on a long line as its common sense that those higher frequencies are going to be useless.

Just a thought though, is it actually possible to force ADSL2 from a VDSL cabinet by unticking VDSL in the options of the HG612? Or is the DSLAM locked to VDSL to prevent crosstalk with exchange connections?

I await correction from someone more knowledgeable than I, but I'm pretty sure BT Openreach run all their VDSL2 on profile 17a and prohibit negotiation of any form of ADSL to an FTTC cabinet. I don't want to unplug my HG612 or risk my FTTC DSLAM port disabling itself and needing to be reset. If you have an FTTC line and are feeling brave, you could try connecting an ADSL2+ device (or disabling all flavours of VDSL on a hacked HG612) and see what happens.


In theory, VDSL2 should perform roughly the same as ADSL2 on long lines. However, to protect the weaker ADSL signals that have come from the exchange from strong VDSL2 signals generated at the cabinet, the UK frequency plan limits the allowable power on the lower VDSL frequencies which are shared with ADSL2+. This means FTTC a long way from the cabinet can land up performing worse than ADSL, because there isn't much usable bandwidth above the ADSL2+ frequencies and the power is limited on the shared frequencies.

If you could negotiate ADSL2+ to an FTTC cabinet, it wouldn't help because you'd be subjected to the same power cut-offs as a VDSL2 device. You may find the discussion in this thread interesting, especially this post of mine.

Edited by deleted (Mon 28-Jan-13 03:35:46)

Very interesting, but I am on Digital Region which supposedly ARE removing their 70Mbit limit on the Max service soon.

Although considering they seemed to originally plan to offer a proper Max service from day one of Max being available,then pulled back. Iit makes you wonder what the specific problem was with the line cards preventing full speed?

It makes you wonder if it was an issue with interference with ADSL lines or something.

Getting back on-topic though, how do the ADSL2 bands compare to VDSL2?

Edited by alexatkin (Mon 28-Jan-13 03:00:06)

In reply to a post by alexatkin:

Getting back on-topic though, how do the ADSL2 bands compare to VDSL2?

VDSL2 profile 17a uses 4096 carriers at 4.3125kHz spacing. ADSL and ADSL2 uses the bottom 256 of these carriers. ADSL2+ uses the bottom 512 of these carriers. The higher the frequency, the greater the attenuation, so the lower the signal to noise ratio on a longer line.

All forms of ADSL put the upstream on the lowest frequencies. VDSL2 uses a more complicated structure, with up to three blocks of upstream and downstream frequencies spread through the available frequencies. This tries to ensure that available downstream and available upstream bandwidth decrease in proportion to each other.

In reply to a post by alexatkin:

Just a thought though, is it actually possible to force ADSL2 from a VDSL cabinet by unticking VDSL in the options of the HG612? Or is the DSLAM locked to VDSL to prevent crosstalk with exchange connections?

No. I tried that a long time ago & a connection couldn't be established.

I have also tried forcing it back to 8c via telnet commands & that didn't work either.