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Target SNM Reduction After BT Fault

Nocturne
Grafter
Posts: 140
Registered: 01-08-2007

Target SNM Reduction After BT Fault

Following a BT Line fault CS are resolving a problem with my Bras Profile which is stuck.
Once this is sorted I hope to make progress on another issue.

At the end of my MaxDsl Trial in May, my Target SNM was 6 dB.
As a the fault progressed my Target SNM has increased to 15 dB.

I now have line stats which are better than they were at the end of the Trial.
The variation in SNR is significantly less.

I can maintain sync in excess of 5500 with a total SNM variation of about 4 dB.
The margin rarely drops below 14 dB with a very occasional drop down to 12.5 dB.

I estimate I should easily cope with a Margin of 9 dB and almost certainly 6 dB.

So has anyone got their SNM reduced following a BT fault.
10 REPLIES
N/A

Target SNM Reduction After BT Fault

In short.. you'll be lucky to get it *reduced* (BT will say no)

You can probably get round this by requesting a line retrain.
Phileasfrog
Grafter
Posts: 51
Registered: 01-08-2007

Target SNM Reduction After BT Fault

Hello

There may be light at the end of the tunnel - do a search for a recent thread I raised regarding a drop of Stable Rate following a BT overhead line fault which caused multiple disconnections.

The good news is that it has now returned automatically to the original 8000 although it has taken over 2 weeks. I deliberately left the modem connected for the last week. Whether it would have been quicker if I had carried out the "reboot over 3 days" routine I am unsure, although it did not change when I did so at 1 week after the fault was fixed.
Nocturne
Grafter
Posts: 140
Registered: 01-08-2007

Target SNM Reduction After BT Fault

The response to my ongoing Ticket was

'Max DSL is an adaptive system.
If the line can handle a margin less that you have currently then it will drop it automatically.
It is not a manual process.
The network will adjust your profile every few days usually to set it at the optimum setting.'


I was not fully reassured especially by the 'every few days' bit.

The main problem I fear will be getting my SNM back down to 6 dB or somewhere close.

I was aware of suggestions elsewhere that if you remain connected, without any loss of sync, for 14 days or thereabouts, you should achieve a reduction of 3 dB.
After another 14 days a further reduction should follow.

strawbear: I've never seen anyone anywhere confirm this process has worked for them - yet.

Assuming your Target SNM was raised associated with the fault, which I think it was having read your posts, can you confirm if your Target SNM has returned to its original level or reduced in any way.
Phileasfrog
Grafter
Posts: 51
Registered: 01-08-2007

Target SNM Reduction After BT Fault

Hello johngbrown

I cannot be certain re the SN Margin setting. As you will see from my original post I am fairly close to the exchange and thus would not expect to be hit overly by the margin being reduced (it is currently a steady 15db SN Margin). All I can say is that after the 120++ disconnections I was cut back to 160k download which must be the minimum, possible. This then increased to a Stable Rate of 1500 after a couple of days, and then to 6500, which is where I started to panic as it looked like it was stuck.

I never had a response to my ticket raised as the following night the SR increased to 8000 and thus all was well. Whether there was any manual tweaking from PN I shall never know.

My intention had been to leave the modem on for the "mythical" 14 days of continuous connectivity and see what happened. I shall never know!

Perhaps all that has happended to me is that the rate adaptive mechanism has worked correctly and I began to "panic" too soon!

Best of luck with your endeavours in any event.
Plusnet Staff
Plusnet Staff
Posts: 12,169
Thanks: 18
Fixes: 1
Registered: 04-04-2007

Target SNM Reduction After BT Fault

Hi,

What speed is the line sync'ing at now? As you say our speed reports are showing the speed as 8000kbps. If this is corresponding with an 8Mbps sync rate then there's no point in making any changes.

In theory if the line remains sync'd long enough with a higher than default SNR without dropouts then the target SNR should decrease by 3dB. BT haven't given out specific time lengths for this to happen but I have seen a couple of examples where about 2 weeks seems to work.

We can sometimes raise a fault to decrease the target SNR but these aren't always easy to get done (I've had less than a 50% success rate on the ones that I've done, and at least 1 of the ones that I've had reduced has gone back up again).
N/A

Target SNM Reduction After BT Fault

Quote
Hi,

In theory if the line remains sync'd long enough with a higher than default SNR without dropouts then the target SNR should decrease by 3dB. BT haven't given out specific time lengths for this to happen but I have seen a couple of examples where about 2 weeks seems to work


Dave - do you have anything concrete from BT about this?
Plusnet Staff
Plusnet Staff
Posts: 12,169
Thanks: 18
Fixes: 1
Registered: 04-04-2007

Target SNM Reduction After BT Fault

Not much more than what it says there, when I've asked when I've done a few more they've said it's an automated process and so long as the line remains stable then the target SNR will go back down, but the length of time that the line must be stable for has always been a bit vague. The 2 weeks is from the couple of people I've seen it work for.
Nocturne
Grafter
Posts: 140
Registered: 01-08-2007

Target SNM Reduction After BT Fault

Quote
What speed is the line sync'ing at now? As you say our speed reports are showing the speed as 8000kbps.


I'm syncing at 5824 and have never synced at anywhere near 8000 since the 23rd of May.

I've been synced at between 5664 and 6208 since the 28th September.

My Stable/Data Rate was sat on 500 until CS manually lifted it to 2000 on the 3rd October followed by another manual lift to 5500 on the 4th October where its been ever since.

My actual Noise Margin has never been below 12.5 dB since the repair and then only very occasionally.

It normally sits between 14 and 16 dB.

I assume your comments relate to my original post.
Community Veteran
Posts: 38,216
Thanks: 913
Fixes: 54
Registered: 15-06-2007

Target SNM Reduction After BT Fault

just seen this
post
which seems to confirm Dave's suggested timescale
Quote
The other way is to hold sync for more than 14 days.
There is a mechanism in place to respond to a continuous sync, with a high noise margin, by attempting to drop the margin.
You need, of course, to maintain a 14 day sync period, then take a chance with a reboot, to see if your margin has dropped.
Then repeat until you're back down to 6db.
I've heard of two instances of this happening (one was with a Zen customer).
The difficult bit is to go through 14 days, then 28 days, without a single re-sync!

Ade
Nocturne
Grafter
Posts: 140
Registered: 01-08-2007

Target SNM Reduction After BT Fault

There are a number of references on ADSLGuide, and no doubt elsewhere to this.

The problem at times, as with this quote, is the suggestion of 14 days followed by another 14 days. He then goes on to say holding sync for 28 days after the first 14 day stint.

Typing error, badly worded, open to different interpretation - who knows. The problem is no-one outside BT seems to know how it really works.

If you re-sync prematurely to take advantage of a drop in Target SNM and to commence another stint, you will be back where you started and none the wiser.

Until BT do what any half decent organisation would do and say exactly what the situation is the whole thing ends up as rumour with references to someone hearing of someone who says this happened to them but no certainty of the sequence of events.

My best guess is that BT have so little confidence in some of their systems they don't want to quote the detail because it may well fail as often as it succeeds.

In the meantime we can only hope more people succeed and we get a clearer picture of how it works - assuming it does.

Following my specific query to CS their response:

The network will adjust your profile every few days usually to set it at the optimum setting

Doesn't seem to fit in with the above and the usually reference doesn't fill me with confidence.