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Noise Margin

Toenex
Grafter
Posts: 40
Registered: 25-01-2009

Noise Margin

Hi all,
My downstream noise margin recently went from a stable 6dB to a massive 17dB - upstream is sitting nicely at 5dB.  Downstream line attenuation is 24dB.  I've not had any noticeable problems with sync rate and I still get 7000 Kb. 
Who do I need to talk to to get this changed?  Is it plusnet or BT?  Are there any tests on the line I can perform?
-tony
9 REPLIES
scootie
Grafter
Posts: 4,799
Registered: 03-11-2007

Re: Noise Margin

The new line mangment on 21cn is alot more responsive and if your line stays pretty stable over the next week or 2 the noise margin should reduce hopefuly back to 6db  on the first target change if not it will do it in steps.
iam on 50db atten and been up an down the noise margin ranges a few times now with out having to get BTw to reduce it like on 20cn
did you plug any thing in to the phone line or hav a thunder storm ect that might of caused the DLM to up your target
VileReynard
Seasoned Pro
Posts: 10,797
Thanks: 241
Fixes: 10
Registered: 01-09-2007

Re: Noise Margin

I've got similar problems.
I've just received a rather promising response from Plusnet (RA at BOT - DSL Logged Faults).
Quote
I've now sent the fault to BT for further investigation and we'll keep you updated. We'll see if they can reduce the SNR and remove any banded profile first.

Does anyone know what a "banded profile" is?

Toenex
Grafter
Posts: 40
Registered: 25-01-2009

Re: Noise Margin


Nothing new plugged into the line, obviously had a few thunderstorms over the last few weeks but couldn't tell if there was any evidence of causality.
I'm running RouterStats and have been monitoring the SNR over the last 24hrs and it is now down to 14dB and hasn't actually been as stable as I thought.  It's jumped around a bit between 17 and 12 quite a lot overnight before settingly back to 17 until 9 am when it dived down to 14 and has stayed there (maybe a graph would have been more appropriate than all that I'll investigate).
I've also installed a DGTeam firmware on my dg834g box as it is, apprently,  less buggy and provides a few linetest options, however I've no idea what to run or why.
VileReynard
Seasoned Pro
Posts: 10,797
Thanks: 241
Fixes: 10
Registered: 01-09-2007

Re: Noise Margin

Does the noise margin change noticeably when you make/receive phone calls?
Are you using the BT master socket?

Toenex
Grafter
Posts: 40
Registered: 25-01-2009

Re: Noise Margin

No change on the phone.  Connected to the master socket and even tried the BT test with no change.
Is there any way to find out if BT have done any work in our area?  I guess it could be the local loop.  I'm connected to the HEATON MOOR exchange if by chance anyone else is connected to that.
scootie
Grafter
Posts: 4,799
Registered: 03-11-2007

Re: Noise Margin

mr evil take a look here for banded profile  Wink http://community.plus.net/forum/index.php/topic,77267.0.html
Toenex
Grafter
Posts: 40
Registered: 25-01-2009

Re: Noise Margin

There certainly appears to be some parallels there, plus it fits with my natural desrire to blame BT for the problem!  Angry  Nice detective work asbo dog.
In my case I did have a much better downstream sync or around 11-12Mbs and my upstream (since uncapping) has remained pretty stable at 1.2Mbs (thank you PN!) so I'm pretty sure my line is basically solid.  I suspected that something was imposing a limit either automatically, such as some random decision by the DSLAM for who know's what reason, or manually by BT.  Banding certainly appears to fit that.
Is there someone at PN I can contact to look into this?
itsme
Grafter
Posts: 5,924
Thanks: 1
Registered: 07-04-2007

Re: Noise Margin

You have to monitor the Interleave depth as well. What I have noticed is that the DLM will increase the SNRM but then switch the interleaving off, Also it has nothing to do with the DSLAM as ADSL2+ lines are connected to a MSAN  Wink
Community Veteran
Posts: 1,169
Thanks: 7
Registered: 01-08-2007

Re: Noise Margin

I had trouble with our noise margin being increased to around 15db iirc and after investigation PlusNet eventually got BT to lower it to 9db.
After months on that, we had a power cut last Wednesday so the line reconnected and it looks as though the noise margin has dropped back to around 6db, which is where it used to be with ordinary ADSL. (Of course there's now an increase in the connection speed though the stable rate hasn't gone up up as yet.)
The point of this is that given time it seems it eventually goes back down to where it should have been all along, though in our case it was a via resynch caused by something beyond our control.
Plusnet user since November 2003
Currently on Unlimited Fibre Extra and Unlimited UK & Mobile Calls