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DMT and ADSL2+

Community Veteran
Posts: 38,460
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Registered: 15-06-2007

DMT and ADSL2+

http://forums.thinkbroadband.com/btsupplier/f/3610069-snr-margin-tweaking-on-wbc.html?vc=1
Quote
I've recently been switched to ADSL2+ on a WBC enabled exchange. I've always used DMT tool to tweak the SNR margin and get a much improved sync, but now around 3 weeks after the switch to ADSL2+ (which did nothing to improve my sync speed btw), I find that DMT is no longer able to force a lower SNR margin.
Various posts on this forum have suggested that BT now have the ability to prevent margin tweaking on WBC, although speaking to my ISP (Aquiss) they claim this isn't done. I'm at a loss to explain this sudden change in any other way, given that nothing has changed at my end.
Does anyone have any definitive information about this situation? Currently it looks like a move to an LLU provider is my only hope of restoring my line speed.
For reference prior to this change I routinely synced at 5.2Mbit with tweaking. Now it will only sync at a shade over 3Mbit on ADSL2+, which is a fairly substantial drop. If I force an ADSL1 connection it rises to 4.5, but again no tweak is possible.
Have the guinea pigs here seen anything similar
22 REPLIES
James
Grafter
Posts: 21,036
Registered: 04-04-2007

Re: DMT and ADSL2+

I can't recall seeing anything similar from any of the trialists so far.
Superuser
Superuser
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Registered: 06-04-2007

Re: DMT and ADSL2+

I don't think anyone has mentioned that.
David
Euge
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Posts: 502
Registered: 11-10-2007

Re: DMT and ADSL2+

That thread also seems to suggest that for some people adsl2 is better than adsl2+. I assume you'd have to pay extra for the uncapped upstream on adsl2 but is probably worth it for the better line speeds. So when I get moved over to adsl2+ soon and I witness no improvement will it be possible to be moved to adsl2?
Community Veteran
Posts: 38,460
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Registered: 15-06-2007

Re: DMT and ADSL2+

Latest update - I don't know how factual it is http://forums.thinkbroadband.com/btsupplier/t/3612655-re-snr-margin-tweaking-on-wbc.html
Quote
Well I've had confirmation that indeed BT have indeed put the block on tweaking on 21CN. Can't say it surprises me.
VileReynard
Seasoned Pro
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Registered: 01-09-2007

Re: DMT and ADSL2+

Quote from: Euge
That thread also seems to suggest that for some people adsl2 is better than adsl2+. I assume you'd have to pay extra for the uncapped upstream on adsl2 but is probably worth it for the better line speeds. So when I get moved over to adsl2+ soon and I witness no improvement will it be possible to be moved to adsl2?

I can confirm (from personal experience) that if you are making little or no use of the wider frequency spectrum of ADSL2+, that your modem will fall back to ADSL2 (which uses the same bandwidth as ADSL1).
You retain the same upstream bandwith - because low frequencies work well with ADSL. - it would appear that you may lose a small amount of downstream speed though.
I've got a ticket open and BT called today (useless!) - so I'll have to wait before I try a tweak.
I do recall running DMT to force my noise margin down to 4dB a few weeks ago, on ADSL2 - but this was in the midst of a sea of troubles etc...
Perhaps it depends on router model?

scootie
Grafter
Posts: 4,799
Registered: 03-11-2007

Re: DMT and ADSL2+

i would test this out for you oldjim but at the mo my lines holding on to this rate at mo and dont want to rock the boat as you can see there is not much room left with the snr max rate is hovering 4300-4500kbps over  this first night on adsl2. fingers crossed it keeps the snr on the tones at this level.
bitswapping seems to be doing a gd job on the msan's
Noise Margin:     9.2   dB
Connection Rate:  4143  Kbps
Line Attenuation: 50.0  dB
Max Rate:         4352  Kbps
carrot63
Grafter
Posts: 599
Registered: 12-07-2007

Re: DMT and ADSL2+

I think I can confirm this is the case. I bought a Sky DG834GT a couple of months ago and reflashed it with the DGteam firmware, using the SNR tweak to drop the SNR to something more reasonable. The line was generally stable but would lose sync once every couple of weeks - no big deal. Max possible tweak seemed to be about 6db, which seems to fit with what's reported elsewhere. However the last couple of weeks it's all been going a little odd, with the tweak not producing quite the expected results, and now, finally, no change whatever. Irrespective of settings (1%, 50%, 140% - no change), I now get 2848 downstream at about 11.5db SNR. Att is also 2.5 higher than norm at 55db.
Since this is with the iPlate I recently installed (which had initially yielded good improvment), my speed with that removed would work out substantially lower than my pre ADSL2+. I'll try removing the iPlate tomorrow just to make myself really miserable.
BTs pointless, inconsiderate nannying  has at least made LLU finally look good and helped me make a decision;  my association with BT serviced ISPs will be ending with my contract, and along with it 8 years with PlusNet.
VileReynard
Seasoned Pro
Posts: 10,991
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Registered: 01-09-2007

Re: DMT and ADSL2+

My modem reports an attenuation 3dB greater in ADSL2+ mode than ADSL2 mode - which seems appropriate as the bandwidth is double for ADSL2+.

carrot63
Grafter
Posts: 599
Registered: 12-07-2007

Re: DMT and ADSL2+

I don't think that's it in my case. The attenuation used to be 55db on max, occasionally 54, but since I've been on ADSL2+ it's been wandering around from 52 to 54.5 which I something I don't think I've seen before - if I rebooted 3 times in 3 minutes, I'd likely get 3 different figures anywhere on that range. But it now seems fixed on 55.
I suspect the deteriorating performance and occasional bouts of 'noise' (pushing the SNR  up) might well be down to the line from my flat to the street which has deteriorated over time in the past, and I'd thought perhaps this was where the fluctuating SNR came from. I'm not so sure now.
But then the resyncs often seem to coincide with the frequent visits of an openreach van to the manhole over the street.
Having less speed than I did two years ago is tedious in the extreme.
VileReynard
Seasoned Pro
Posts: 10,991
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Registered: 01-09-2007

Re: DMT and ADSL2+

When I was on MAX, my Netgear reported 27.5dB for well over a year - never anything different.
The two routers I've tried on 21CN have always reported
24dB (ADSL2)
37dB (ADSL2)
I had a BT man round yesterday who thought I had an excellent line.
He measured the attenuation to the exchange as 36dB Smiley
I'm on about 6.2Mbps sync, 10dB noise margin - rubbish!

carrot63
Grafter
Posts: 599
Registered: 12-07-2007

Re: DMT and ADSL2+

I'd rather your rubbish than my rubbish  Angry
VileReynard
Seasoned Pro
Posts: 10,991
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Registered: 01-09-2007

Re: DMT and ADSL2+

[gloat]I used to sync at 7.3Mbps when I was on the "slower" ADSL MAX[/gloat]

scootie
Grafter
Posts: 4,799
Registered: 03-11-2007

Re: DMT and ADSL2+

mine just droped after holding up overnight at 12db target now dropped at 14.20 and given me a 15db target. my adsl line stayed synced at the current sync ive got on 12db target for weeks.
time to have play with tweaking.
carrot63
Grafter
Posts: 599
Registered: 12-07-2007

Re: DMT and ADSL2+

Quote from: ASBO
time to have play with tweaking.

If you're on ADSL2+, a fiver says it won't work Asbo.