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

[#1]

Quote from: rockradio

A lower noise margin will eventually cause your modem to loose sync, therefore that proves higher is better ... Obviously I've had it wrong this past 35 years ...

It depends on the characteristics of the noise of course, so such an absolute statement is just no possible.
Yes, if the exchange asks for a higher SNR margin, the line should be more stable. But ... if the target SNR is 6dB and the noise on the line only varies by 3db up or down, the line is going to be stable. Even if the noise increased to 6 or 9db for short periods of time, i.e. few hundreds of millseconds, the line will cope, as generally only a small number of the tones are affected by this noise and the other tones work just fine, with lower throughput. If the noise increases to 9db and stayed there, Yep probably the line stopped working.
It all depends on the chracteristics of your line and the noise affecting it. An absolute statement is not possible.
Like most generalised statements they tend generally to be wrong.
SW.

[#2]

Nothing yet on how widespread this jump to 15dB might be

[#3]

Our noise margin never went over 10 and rarely reached anything like that prior to the recent sudden jump to 15; not even when we were having problems with a noisy line and speed fluctuations last year when it was anything from 0dB - 7db iirc.
Since I messed around with telnet and set the target SNR lower, it's been hovering around the 9 - 10 mark with a steady speed of 4000kbps and I haven't switched the router off since Saturday night. I first set the target to 6 and then to 3 when I next switched it on (Sat night) but it isn't going below 9. Obviously, I don't want to mess around with it too much or BT's automatic system might set it even higher than 15!

[#4]

Is anybody at PN aware of a recent increase in reports of SNR margin jumps of more than the normal 3db amounts we expect from RAMBO/DLM ?
Can somebody post the Delta reports on my line for the past 30days here or do I need to raise a ticket, I'd like to check them against my router logs ... which will be fun.
SW.

[#5]

Not specifically noticed a massive change to be honest.
Does this help?

[#6]

Thanks James. Stellar help as usual.
I have opened ticket 25627911 asking for the margin to be put back to 9db, CSC are asking me to 'wait 3days, etc'.
Does the column called "Noise Margin Reset (Y/N)" actually show on which days the target margin was changed? And so it shows on June/29th and July/2nd that BT did increase the margin by 3db on each of those days?
regards,
SW.

[#7]

I got the same response from CS - I will be interested in your experience as I still don't quite believe it - previously it used to be 14 days stable connection with no resynchs at lower speeds.
At present I have got round the problem by downgrading the firmware on my Speedtouch and using DMT - now at 12dB and may try 9dB after a while

[#8]

Yep, I think that's what it's referring to.
Just reply back to the ticket that a target noise margin has been changed and you want it changed back, refer to me if needs be.
The response you got in itself wasn't incorrect, just needs an understanding of what needs doing.

[#9]

I've managed to force my noise margin back from 12dB to around 9dB (it actually varies between about 8.8 - 9.1dB (which is what it should do). I've a long term history of running at 5 - 6dB.
So things are a bit on the slow side for me.
It's actually very difficult to get your noise margin reset by going through the official channels.
I know that if I persevere and get it changed, BT will just screw it all up again within a couple of months.
I don't have the time to get it sorted properly.

[#10]

£10 says I can get it changed within 6 hours...

[#11]

To 15dB?

[#12]

Quote from: axisofevil

BT will just screw it all up again within a couple of months.

Thats a fact.
I am hopeful that ADSL2+ will be impelemented properly, so the target margin is always 6dB, the system then gracefully adapts the rates based on your phone line at all times ... this is what the spec for ADSL2+ says it should do. For mean it would mean +3Mb during the day and just over 2Mb overnight, that would do me just fine.
Lets hope BT do it properly! I live in hope.
SW.

[#13]

Quote from: Jameseh

£10 says I can get it changed within 6 hours...

I know you can get it changed quickly, but as it happens I've just submitted a "fault report".
I just know that I'll get stuff about filters etc...
I'll repeat what I said and it'll get to networks...
They will request BT to change it.
Nothing will happen.
I'll ask them to forward it to you - and things will happen!
PS Can I keep my £10? (please?) - I've every confidence in you.

[#14]

Remind me in the morning and I'll raise a fault if it hasn't already been done by then and I'll chase it later on (I'm in meetings allllll afternoon though).

[#15]

PS: You can keep your tenner