cancel
Showing results for 
Search instead for 
Did you mean: 

Mysterious BTW Line Profile Behaviour

jack21
Grafter
Posts: 180
Registered: 25-02-2009

Mysterious BTW Line Profile Behaviour

I wonder if anyone can suggest what might be going on with a BTW Line Profile well below the present ADSL2 sync rate, which is 'capping' actual thruput rates.
My replacement long rural line (many thanks to Plusnet and a very special Openreach engineer)  is 58db attenuation and has just reached the end of its 'training period'. It has dropped-out a few times during the period, always apparently due to DLM making a change in either default SNRM or interleaving depth. The line performance is now as good as the best lines in my village and the sync rate (around 3600kbps) and default SNRM of 3 (astonishingly stable - holds on even in storms down to 1) are admirable. The Plusnet Profile is at the appropriate 88.2% of sync rate - 3.2Mbps - but the BTW profile is seemingly stuck at 2.12Mbps since day 1 of the training period, and won't do its ADSL2 88.2% expectation......all speedtests return 2.28Mbps as the actual thruput.
I'm having some difficulty in having this recognised as a correctable problem, and it seems an awful shame to be limited to 2.12Mbps downstream for downloads when the line and sync rate are so good.......any ideas?
34 REPLIES
jack21
Grafter
Posts: 180
Registered: 25-02-2009

Re: Mysterious BTW Line Profile Behaviour

Apologies for replying; I've just been trawling the Forum (should have done that first !!!) and it appears that this is not an uncommon problem with 21CN and ADSL2.....profile banding!  My unfamiliarity with the issue is partly due to the local exchange being upgraded from 20CN to 21CN only 3 months ago, and my line pair renewal a few weeks ago has only then provided me with above-2000kbps sync rates.
From the answers in the Forum it seems quite a difficult thing to completely escape from........so I'm considering switching my router back to ADSL1 to see if that bypasses the problem. Has any reader done that, and was it successful?
Superuser
Superuser
Posts: 11,099
Thanks: 2,471
Fixes: 22
Registered: 22-08-2007

Re: Mysterious BTW Line Profile Behaviour

Hi Jack,
I do not think banding is the issue here, if it was, you'd not have the synch speed you have and the appropriate PN profile.
Expectations: 58dB attenuation -> line sych @6dB = 3200kbps
@3dB 3600kbps is right on the nail
3600 raw synch = 3175 data profile (3.1Mbps)
In this case the odd bit here is the BT profile.  Looking at posts elsewhere as I understand them, this is going to cause the DLM to drop data (as it has no buffering) and consequently markedly degrade data transfer speeds.  I'm guessing that this causes similar problems to the PN profile being too high.
Something is not quite right with BTOR's systems here, I do not think this is not related to banding, I recommend leaving it alone until the DCT guys can take a look for you.
jack21
Grafter
Posts: 180
Registered: 25-02-2009

Re: Mysterious BTW Line Profile Behaviour

Hiya Townman,
I think you're probably right on all accounts; that BTW 2.12 profile seems well and truly stuck, and I did briefly have it at 2.9 and corresponding speed tests too.......but not since the training period began and then ended.  However, I'm having difficulty getting it recognised and attended to. The consequent speedtest always is either 2.28 or 2.29.......so suspicious that it is always EXACTLY that rate.
About an hour ago, I decided to try the ADSL1 experiment, and I have retrained line/router using G.DMT rather than ADSL2 so will try to last 3 days like that to see what the BTW profile does.
These rates contrast with my previous line pair which gave 69-70db attenuation, best rates of briefly 2050 and average 1800. But frequent HR issues lead to me being given this better line.
Superuser
Superuser
Posts: 11,099
Thanks: 2,471
Fixes: 22
Registered: 22-08-2007

Re: Mysterious BTW Line Profile Behaviour

Quote from: jack21
The consequent speedtest always is either 2.28 or 2.29.......so suspicious that it is always EXACTLY that rate.

Not really - the DLM has become the choke point of the end to end service, everything else is happy to run faster, therefore your data transfer speed is running as fast as the choke point will allow.  Something is amiss here.  Sight of your ADSL stats would be interesting.
jack21
Grafter
Posts: 180
Registered: 25-02-2009

Re: Mysterious BTW Line Profile Behaviour

Current line details on ADSL1 are:
DOWN
Noise margin    6.2              (tweaked UP by 140, as unsure yet if ADSL1 will 'live' at 2-3 where ADSL2 was happy)
Connection Rate 3488
Attenuation 59.0                  (ADSL2 is 58.0)
Power 17.9
Max rate 3712
UP
6.0
704 
31.5 
12.5
868
Superuser
Superuser
Posts: 11,099
Thanks: 2,471
Fixes: 22
Registered: 22-08-2007

Re: Mysterious BTW Line Profile Behaviour

Jack,
This is worse than it was.  I would recommend putting things back to default less "manual adjustments" causes more confusion.  Then allow the DCT guys to look into the real issue.
Plusnet Staff
Plusnet Staff
Posts: 6,346
Thanks: 31
Fixes: 5
Registered: 26-11-2011

Re: Mysterious BTW Line Profile Behaviour

I've just taken a look at the line and I've found an inconsistency with the speed data taken from your lien and the speed data stored on our suppliers systems.
I've raised a case with our suppliers for this to be investigated. Our Faults Team will keep an eye on this and will update you in due course.
Chris Pettitt
Cloud Environments Engineer
jack21
Grafter
Posts: 180
Registered: 25-02-2009

Re: Mysterious BTW Line Profile Behaviour

Hiya Townman,
It is a lower sync rate, but I've sacrificed some sync speed to gain an snrm that gives more of a safety buffer as I've never had an ADSL connection that would survive below 3db......last night's usual gradual snrm decrease of 2db took it down to 5.5db without dropout.  In due course, if ADSL1 sorts out this stuck BTW profile (Huh), I will reduce the tweak level, or perhaps more preferably, return to ADSL2.
The thing is that Plusnet Faults Team have said that because the BTW profile is at a level that is above the BTW estimate for my area, and that my sync rate is well above the estimate, they won't raise a fault with BTW........quite a hard view, in my opinion, but since they and BTW got me onto a much better line pair, I'm less inclined to criticise.
Quote:
I have reviewed and tested your line and I have been unable to locate any settings causing your speed to restrict and cap.
As this speed is above the estimated speed for your area, we would be unable to raise this as a fault.
Should this speed further deteriorate, please do not hesitate getting back in touch.
EndQuote
jack21
Grafter
Posts: 180
Registered: 25-02-2009

Re: Mysterious BTW Line Profile Behaviour

@Chris
Thanks for that, Chris, I had thought that I'd not made progress via the faults ticket on this issue, so I'm very appreciative of your intervention.
jack21
Grafter
Posts: 180
Registered: 25-02-2009

Re: Mysterious BTW Line Profile Behaviour

@townman and @chris
I've just reverted the router to untweaked ADSL2 ;  now running at 3766 at 3.3db
Superuser
Superuser
Posts: 11,099
Thanks: 2,471
Fixes: 22
Registered: 22-08-2007

Re: Mysterious BTW Line Profile Behaviour

Jack,
Sounds like a result - I'd suggest that you leave things alone, keep monitoring the router stats, PN profile and running speed tests on BTW.
Cheers,
Kevin
jack21
Grafter
Posts: 180
Registered: 25-02-2009

Re: Mysterious BTW Line Profile Behaviour

Update: Things changed yesterday/overnight.......the line resynced 3 times, first at midday caused by DLM raising default SNRM to 6 and interleaving depth change, then 2 further unexplained ones close together in the late afternoon. Then this morning I find the BTW profile is at the correct level for the sync rate, and the Plusnet one too.
And the 'acceptable range of speeds' is back to what it used to be.
************************************************************
Download speedachieved during the test was - 2.85 Mbps
For your connection, the acceptable range of speeds is 1.2 Mbps-4 Mbps.
IP Profile for your line is - 2.88 Mbps
************************************************************
Thank you muchly for your intervention, Chris (could you close the ticket), and to you Townman for your valued advice.
Jack
Plusnet Staff
Plusnet Staff
Posts: 6,346
Thanks: 31
Fixes: 5
Registered: 26-11-2011

Re: Mysterious BTW Line Profile Behaviour

Hi Jack,
I can see the line has retrained 4 times within the last 24 hours, something is driving a high number of errors on your line, we need to find out why. Our Faults Team have your details and will be working on your fault as soon as they can. It's very likely that we'll require an engineer to visit to take a look at this so we can try and identify the source of the errors.
Please ensure that all your internet equipment has been ruled out that could be causing the issue.
Chris Pettitt
Cloud Environments Engineer
jack21
Grafter
Posts: 180
Registered: 25-02-2009

Re: Mysterious BTW Line Profile Behaviour

OK Chris, willdo.
I had been thinking about trying again with the intermittent high error rates problem. I first noticed the issue several years ago and raised a faults ticket about it, but the cause was never identified and since then I simply tolerate it. I've discussed it with Openreach engineers when they've been here on other calls, but nowt came clear. I haven't pushed it because I'm concerned that a Openreach  'solution' may be to raise the default SNRM to 15, although I've tried that myself and it has little effect.
The high CRC rates occur mainly from around day no. 80 in the year and usually finish mid to end october...........though sometimes during the winter there may be a brief hour or so burst. After an initial splurge lasting 2 weeks, the issue happens sporadically and unpredictably until oct........I can have weeks of service with no sign of the high CRCs, but then I'll get an hour/day/days of them.
On/around day 80, for perhaps a few days, I see brief spikes of high CRCs, then a week later they begin in earnest and continue solidly for around 2 weeks - at rates normally around up to 160/min but rarely sometimes soaring to 1000's/min (makes internet unusable so I then turn off router overnight). At the 160/min level, I got normal speedtest and download rate results, and the high rates were not accompanied by any SNRM dips....and I maintained a default SNRM of 6.
The pattern of the rate increase is of a gradual increase from the norm of 0.2/min over several hours, almost in a wave-like pattern on Routerstats, reaching a peak and then 'waving' along for days/hours until gradually decreasing over several hours, then a quick brief high spike, then back to normal. Occasionally, whilst at the high peak wave , the rates instantly plunge to almost zero, then maybe 30 mins to an hour later, instantly begin at the high peak value.
All this whilst router plugged inside engineers socket. Different routers, filters, cables, phones (even new telegraph pole) do not affect it.
My line has just been replaced from exchange to village cabinet, to subsidiary cabinet, so the only bit of the original line is from the subsidiary cabinet to home. The most recent Openreach chap gave extensive attention to testing the line and pronounced it now excellent.
If I had to attempt any correlation as to cause, I would say that the problem does not occur in wet or cold periods (eg yesterday - warm and dry, problem present, whereas today - cool and wet, problem absent).
Since ADSL2 arrival in Jan, I've noticed that DLM applying interleaving of 32, 64 even 96 alleviates the problem, but I assume that it just shifts the errors from CRC to FEC.

Jack