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Stability plummeted - more info provided

Community Veteran
Posts: 1,125
Thanks: 4
Registered: 14-08-2007

Stability plummeted - more info provided

Stats while I'm home - more info to follow when there is time.
Modulation : ADSL2+
Annex Mode : Annex A/L
Line State : up
Lan Tx : 26115906
Lan Rx : 13293857
ADSL Tx : 6381
ADSL Rx : 5679
CRC Down : 0
CRC Up : 0
FEC Down : 0
FEC Up : 0
HEC Down : 0
HEC Up : 0
SNR Up : 7.3
SNR Down : 8.6
Line Attenuation Up : 9.7
Line Attenuation Down : 15.0
Data Rate Up : 1064
Data Rate Down : 14693
21 REPLIES
Community Veteran
Posts: 4,852
Thanks: 121
Fixes: 24
Registered: 14-07-2009

Re: Stability plummeted

I cannot see anything in those stats to indicate instability.  Except perhaps that you have no recorded errors of any type which, being too good to be true, might imply that the connection has not been established for very long.
Community Veteran
Posts: 1,125
Thanks: 4
Registered: 14-08-2007

Re: Stability plummeted

I need to provide more information - subject amended accordingly
Community Veteran
Posts: 1,125
Thanks: 4
Registered: 14-08-2007

Re: Stability plummeted - MORE INFO TO FOLLOW

Many months ago, I was connecting at nearly 20mb/s and 3db margin.
Then at about the same time as some packet loss exchange capacity issues, my profile changed and I became locked onto a 15mb noise margin/15mb/s speed. This is all documented in the thread of the time here:
http://community.plus.net/forum/index.php/topic,122181.0.html
Most interesting was that the speed stability setting (possibility to manually adjust SNR) in the router had no effect. SNR stayed locked at (more recently) 15db.

In the end I didn't bother pursuing it further because cab was due to be upgraded for FTTC, and I decided I could live with the situation until then.
In the meantime, btw checker stated cabinet now upgraded for FTTC, and an engineer came out to install. Installation not completed because cabinet was still being installed.  Roll eyes
Then this morning I got up - no internet. Checked router stats - 21mb/s but -3db SNR. Looked at stability adjust settings in router, and these had been left at -4 from previously when they were having no effect. Disabled that, and I still had 21mb/s but -3db SNR (and continually restarting connection)
So I set the stability setting to +10 (maximum) and the connection became stable at 10mb/s +12db. Further adjustment to +6 gives the stats you see above.
Im guessing a setting has been changed somewhere due to the failed FTTC install.
Questions
What has changed to make the stability adjustment suddenly start having an effect again.
Why with stability adjustment turned off does SNR Drop to -3 (causing unusable internet)
Why with 15db downstream attenuation am I only getting 15mb/s at SNR of 7db

Any insights appreciated.
Community Veteran
Posts: 1,125
Thanks: 4
Registered: 14-08-2007

Re: Stability plummeted - MORE INFO TO FOLLOW

BT Test results
Results Image not loaded

1. Best Effort Test:  -provides background information.
Download  Speed
12.25 Mbps

0 Mbps 21 Mbps
Max Achievable Speed
Download speedachieved during the test was - 12.25 Mbps
For your connection, the acceptable range of speeds is 4 Mbps-21 Mbps.
IP Profile for your line is - 12.96 Mbps
2. Upstream Test:  -provides background information.
Upload Speed
0.19 Mbps

0 Mbps 0.83 Mbps
Max Achievable Speed
Upload speed achieved during the test was - 0.19Mbps
Additional Information:
Upstream Rate IP profile on your line is - 0.83 Mbps

We were unable to identify any performance problem with your service at this time.
It is possible that any problem you are currently, or had previously experienced may have been caused by traffic congestion on the Internet or by the server you were accessing responding slowly.
If you continue to encounter a problem with a specific server, please contact the administrator of that server in the first instance.
Please visit the FAQ if you are unable to understand the test results.
Community Veteran
Posts: 4,852
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Fixes: 24
Registered: 14-07-2009

Re: Stability plummeted - more info provided

I have no idea how you are adjusting the 'stability setting' on your router as most routers do no have any such setting.  With a few routers and the right software you can mislead the DLM by feeding-back the wrong numbers for the SNRM seen by the router, the effect being to change the effective target SNRM.
If you remove any such settings you can then see what SNRM the DLM is actually targeting.  My guess would be that it has finally dropped the target SNRM after making it very high (15dB).  The DLM is very slow to forgive but it does so eventually if your line appears stable.  But if you try to push your line too hard by tampering with the 'stability' to the point where it becomes unstable then you will find yourself back at 15dB. 
Plusnet Staff
Plusnet Staff
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Registered: 26-11-2011

Re: Stability plummeted - more info provided

If you were affected by last night's outage, this is likely to be the cause of instability for about an hour or so up until around 20:10.
Chris Pettitt
Cloud Environments Engineer
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Re: Stability plummeted - more info provided

@ReedRichards
I believe the facility is effectivley changing the target SNR. BUT I did disable it, and after disabling, the Stats showed -3DB and 20+mb/s (presumably DLM set), but totally unsusable due to continuous dropping the connection. Finger trouble is possible (I was short of time this am) So I'll try again tonight with it disabled.

@Chris
No it was fine until midnight last night. Problems were present at 6:00am when I got up. Perhaps you could check the connection quality chart(??) for me (the one that shows disconnections) to see when the issue started.
Thanks.
Plusnet Staff
Plusnet Staff
Posts: 6,346
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Fixes: 5
Registered: 26-11-2011

Re: Stability plummeted - more info provided

I see what you mean!
<img src="http://community.plus.net/visualradius/generated/image14050769552070.png"/>
It looks to have stabilised now and you've avoided any line banding. I've just done a thorough check, so apologies for the connection drop. Your SNR is a little on the high side, considering the Target is 3db. I'd give the line time to settle down again, but if it start to drop out again, I'd look at raising a fault at http://faults.plus.net
Chris Pettitt
Cloud Environments Engineer
Community Veteran
Posts: 4,852
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Registered: 14-07-2009

Re: Stability plummeted - more info provided

Yes, what happened this morning between ~5 am and ~7am is exactly what you don't want to happen.  That is unless the DLM has had an aberration and set your target SNRM to a lower value than it can cope with - which could happen if you have been feeding it with false data.
Community Veteran
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Registered: 14-08-2007

Re: Stability plummeted - more info provided

Hi Chris
Thanks for that - so started around 4:30am.
Since Febraury and until this morning, the "stability" setting in the router has been ignored (And I've been locked on around 15db snr - even though the target has been 3 - tried with two routers - See thread linked above if you want the full and long story). In previous tests, it had got left at -4 which has the effect of reducing target SNR by 4db. I disabled it, (around 6:30) and STILL the downstream SNR was -3db, with the result  you see in the chart). I've only stabilised the connection by setting the stability adjustment to +6
Any idea why things have suddenly changed in the early hours?
I'm going to disable the stability adjustment tonght to see if the SNR settles correctly at the 3db target.
Community Veteran
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Registered: 14-08-2007

Re: Stability plummeted - more info provided

OK home now (bunked off early  Cheesy )
Disabled stability adjust - my line seems to be back to it's pre Feb state. No idea why it went that way in the first place. No idea why it is back again now. I think I am still on a 15mb/s plusnet profile though - any chance that could be lifted? Also the disconnections I've just done seem to have put me onto a 6db target SNR - great if that could be reset for my last few weeks on ADSL.
Modulation : ADSL2+
Annex Mode : Annex A/L
Line State : up
Lan Tx : 27200054
Lan Rx : 13857945
ADSL Tx : 6
ADSL Rx : 4
CRC Down : 0
CRC Up : 0
FEC Down : 0
FEC Up : 0
HEC Down : 0
HEC Up : 0
SNR Up : 5.5
SNR Down : 6.1
Line Attenuation Up : 9.8
Line Attenuation Down : 15.0
Data Rate Up : 1072
Data Rate Down : 18078
Community Veteran
Posts: 1,125
Thanks: 4
Registered: 14-08-2007

Re: Stability plummeted - more info provided

Results Image not loaded

1. Best Effort Test:  -provides background information.
Download  Speed
13.07 Mbps

0 Mbps 21 Mbps
Max Achievable Speed
Download speedachieved during the test was - 13.07 Mbps
For your connection, the acceptable range of speeds is 4 Mbps-21 Mbps.
IP Profile for your line is - 15.95 Mbps
2. Upstream Test:  -provides background information.
Upload Speed
0.69 Mbps

0 Mbps 0.83 Mbps
Max Achievable Speed
Upload speed achieved during the test was - 0.69Mbps
Additional Information:
Upstream Rate IP profile on your line is - 0.83 Mbps

We were unable to identify any performance problem with your service at this time.
It is possible that any problem you are currently, or had previously experienced may have been caused by traffic congestion on the Internet or by the server you were accessing responding slowly.
If you continue to encounter a problem with a specific server, please contact the administrator of that server in the first instance.
Please visit the FAQ if you are unable to understand the test results.
Community Veteran
Posts: 4,852
Thanks: 121
Fixes: 24
Registered: 14-07-2009

Re: Stability plummeted - more info provided

Quote from: tonyAtplus
Since Febraury and until this morning,... I've been locked on around 15db snr - even though the target has been 3

If the DLM sees your line as unstable it will increase your target SNRM in 3dB increments.  15dB is as far as it goes before you get placed on a 'banded profile' (which amounts to a fixed, slow, line rate).  I cannot help thinking that messing around with the dangerous 'stability' setting on your router made your line unstable.  Perhaps you ended up on a banded profile which is why the 'stability' setting ceased having any effect?
Now that the DLM has finally forgiven you, don't make the same mistake twice.
Community Veteran
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Registered: 14-08-2007

Re: Stability plummeted - more info provided

I didn't touch the stability setting until after it went to 15db (For no apparent reason - even to plusnet-target SNR was still 3db). I was playing with stability settings to see if I could get it down again (plusnet were unable to)