Noise Margin jumped up to 15dB today (Exchange enabled for 21CN)

[#1]

My exchange apparently has been 'upgraded' to 21CN, the consequence appears to be that my ADSL noise margin has jumped from 12dB which it has been sitting at for months, to 15dB, this has resulted in a drop to 2528 kbps from 3000 previously.
"BT Wholesale has set an enablement date of 30/04/2008 for their 21CN Wholesale Broadband Connect product at the Dunfermline exchange"

Can I get PlusNet to get BT to sort this ?

[#2]

If BT stuck to their deadlines, your ADSL connection would have received a short disconnection (and reconnection).

[#3]

Accepted - but normally my Noise margin stays at 12dB.
I have raised a ticket to get PN to ask BT to lower my Noise Margin.
cp:quote

[#4]

While your exchange may have been 21CN enabled, your connection has not as the 21CN is still in an alpha trial which PN are not involved in, so your connection should not have been affected by the upgrade.
So it will just be a coincidence that your connection has changed or some BT engineer pressing the wrong buttons.
You will need to raise a speed fault but specify you want the target noise margin reduced.

[#5]

Thanks Peter, that is what I have done. Yes it may have been coincidence that this happened on the very day they were fiddling at the exchange, but I doubt it. 

[#6]

Just found this thread after having discovered my exchange is now due to be 21CN enabled at the end of the month and looking to see what the latest was from PlusNet on the subject.
I've been wondering why our noise margin had gone up from its usual 5db or so to nearer 15db, with a resultant drop in speed but as we have a guest staying for a couple of weeks, I didn't want to be messing around testing the connection till she's gone. Also, we're now often being connected with the mysterious 15.5db line attenuation that sometimes occurs, instead of our usual 30db or thereabouts.
After reading this, I think I'll just wait and see what happens and only raise a ticket if it's not back to normal when they've finished what they're dong at the exchange!

[#7]

I've had troubles...
Eventually got good sync(7700Kbps), good noise margin, even got PlusNet to give me a good profile (6500Kbps)
BT speedtester showed the same.
However, PN speedtester showed 1400Kbps any time of the day or night,
This was in accordance with general speed of websites.
Raised tickets with PN.
Eventually got back at a decent data rate (3-5Mbps in the afternoon).
My exchange boasts to be going 21CN in the next couple of weeks

[#8]

Am I missing something here?
My broadband is more reliable the HIGHER the noise margin. eg. 5dB would be virtually unusable, 12db ok, but 18db excellent. Noise margin is the DIFFERENCE between wanted signal and noise. The higher the margin the better.
I suspect the drop in speed is only temporary?
In ANY communications system, engineers strive to achieve the highest signal/noise ratio (noise margin)that is possible.
Robin

[#9]

If you are happy with a fixed speed 512 kbps speed you can have a really high noise margin but if you want the highest speed then you want the lowest noise margin which doesn't create problems.
The whole point of the system is to give you the highest stable speed possible not the highest noise margin.

[#10]

Quote from: francoise

Am I missing something here? I suspect the drop in speed is only temporary? In ANY communications system, engineers strive to achieve the highest signal/noise ratio (noise margin)that is possible. Robin

Yes: Noise margin is different to signal/noise ratio.
Noise margin is - roughly "minimum allowed S/N ratio"
The more you hold in reserve, the slower the line (and up to a point) the more stable the line.
So your speed reduction is permanent, unless you do something about it.
Choose a value (6dB is mostly OK) and 18dB ludicrous that allows a few occasional errors.

[#11]

Thanks Jeremy.
That explains all. BTW, I am on a fixed 2M, s/n is usually around 22db. If it dropped to say 10db, i may get problems. This is what i was (incorrectly) basing my comparison on. I always strive for best s/n.
Well, I learnt something today!
OP, good luck with your request!
Robin

[#12]

Quote from: francoise

Am I missing something here? My broadband is more reliable the HIGHER the noise margin. eg. 5dB would be virtually unusable, 12db ok, but 18db excellent. Noise margin is the DIFFERENCE between wanted signal and noise. The higher the margin the better. I suspect the drop in speed is only temporary? In ANY communications system, engineers strive to achieve the highest signal/noise ratio (noise margin)that is possible. Robin

Our noise margin has only recently increased to approx 15db from 5db and suddenly, for no apparent reason. It was fine before, with no disconnections or anything after problems last year that were fixed by a BT chappie cleaning out the connection box at the top of the telephone pole. The line doesn't seem to have developed noise again, which it had with the previous problem.
As I said earlier, I discovered our exchange's switch to 21CN is imminent and then saw here that someone else had a similar sudden increase in noise margin in similar circumstances, so wondered if the two were connected.

[#13]

Quote from: Mad

As I said earlier, I discovered our exchange's switch to 21CN is imminent and then saw here that someone else had a similar sudden increase in noise margin in similar circumstances, so wondered if the two were connected.

Yes - I feel sure that this was the cause of a recent speed dropfor me. However, a ticket to PlusNet has fixed it.
It doesn't seem possible to make a major change and not have it affect broadband in a bad way.
See attached (the green bar shows my noise-margin reaching about 20dB).
[Monitored every 5 minutes]

[#14]

I've also had the noise margin on my line increased from 6db to 15db which has knocked my line speed for 6.  Used to connect in the  2700 - 3300 range, now down to 1300
Plusnet has asked BT to reduce it twice successfully but the failed the 3rd time.  From my perspective at 6db the line was fast and stable, BT reckon that it was fast and unstable so increase the margin.  Now line is just slow. I'd accept this if not for the fact it ran at 6db for the past 2 years with no problem. 
I wonder if BT has some new algorithm to calculate the Target noise margin which is less forgiving than it use to be.

[#15]

Do you have a router where the noise margin can be set externally by software?