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Author Topic: BT DLM advice needed..  (Read 5359 times)

8062282

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Re: BT DLM advice needed..
« Reply #30 on: September 29, 2019, 05:10:13 PM »

Hi - I'd been connected for over a week & there was no intervention by the DLM to put me back to the 39mb I was on previous. SNR has sometimes gone up during the week at night again showing a attainable speed of 45mb+ but I was stuck at 34,995. Decided to bite the bullet this morning & unplugged the DSL lead out the modem for about 20 secs. When I re-connected my speed went up to 34,999. Wow, the excitement. SNR is at 6.4dB & hasn't moved at all since the re-connect at 8am. The attainable speed hasn't budged either, not even 0.005kb. It's constant at 42,395.

I have another dilemma in that something happened at 11.08am which is creating millions of errors. The two downward spikes are me trying to break the connection by changing from 5ghz to 2.4ghz & changing channels without having to re-boot the modem. It didn't work. Due to my DSL disconnect this morning, I'm loathe to re-boot the modem & upset the DLM. Odd thing is, there's no real impact anywhere else. The 1400 US ES was caused by un-plugging the DSL cable. No idea why it does this..

Average error rates for 29 Sep 2019


CRC erors per hour:  2.12 Down,  1.18 Up
FEC erors per hour:  4275911 Down,  3.13 Up
HEC erors per hour:  40.8 Down,  0 Up
ES per hour:         1.47 Down,  83.9 Up
SES per hour:        0.83 Down,  0.24 Up
Total ES in the day: 25 Down, 1422 Up


My question is. Do I leave it in the hope it sorts itself out or do I re-boot the modem?
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burakkucat

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Re: BT DLM advice needed..
« Reply #31 on: September 29, 2019, 07:09:08 PM »

Don't worry about FECs . . . they are no problem. They show that the error detection & correction process is operating successfully. Think of FECs as CRCs that did not happen.

The ones to consider are the CRCs, they are "hard" errors.
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8062282

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Re: BT DLM advice needed..
« Reply #32 on: September 29, 2019, 07:13:32 PM »

OK, thanks. I thought as much. I'll leave it then. It's still going on so I hope the modem isn't having a dicky fit :)
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Weaver

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Re: BT DLM advice needed..
« Reply #33 on: September 30, 2019, 12:17:40 AM »

‘FEC errors’ are errors detected and successfully corrected by the mathematics; ‘CRC errors’ are errors that could not be corrected ? Is that right ?

The terms are being completely inappropriately used; forward error correction is just mathematical error correction by recalculation and a cyclic reduncancy code/check is the mathematical method used or an appended result code produced by a calculation applied to the data. There is no success or failure inherent in the definitions of these terms and such a mention is essential here. Broadcom eg al have been using these inappropriate shorthand labels for so long that we have got used to them.
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burakkucat

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Re: BT DLM advice needed..
« Reply #34 on: September 30, 2019, 01:50:38 AM »

‘FEC errors’ are errors detected and successfully corrected by the mathematics; ‘CRC errors’ are errors that could not be corrected ? Is that right ?

Yes but no but yes . . . I'll point you to a good page, on a web-site that I know, which will explain it far better than I am able to do.
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Weaver

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Re: BT DLM advice needed..
« Reply #35 on: September 30, 2019, 02:58:01 AM »

Quite so, I should have dug out Kitz’ article. It annoys me that the mfrs don’t simply use ‘detected’ ‘corrected’/‘uncorrected’ throughout.
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8062282

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Re: BT DLM advice needed..
« Reply #36 on: October 01, 2019, 08:27:05 PM »



Thanks for the responses. The DLM has banded me at 34,999. Everything was fine at 39mb. Low error count & then bam, DLM kicked in & took the interleaving off completely. Errors galore. Re-synced the following morning & the speed hasn't budged from 34,999. BT tell me I'm now banded at 34,999. Why would the DLM go from one extreme to the other?  It also pains me that they can cap your service at 40/10 & you're expected to pay the same as somebody on 55/10. Why don't they just start everybody off at 55/10?  If you're line ever gets better, you'll never get a speed increase because you're capped.
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kitz

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Re: BT DLM advice needed..
« Reply #37 on: October 02, 2019, 12:17:05 AM »

I suspect your are in a similar situation to me.   I have an odd bout of SHINE type noise that can occur each morning.   Usually the burst is short, but occasionally it sticks there producing thousands of errors within a short time frame.   99.99% of the time my line is perfectly fine with hardly any errors and rock steady SNRM.    Unfortunately though DLM uses something called MTBE over the course of the day.   It doesn't seem to realise that 1/2hr later the line is fine again..  but instead it just thinks "Oh its hit red threshold so lets take action".     It's why I have to watch my line and I even have dslstats set up to alert me if my errors go over a certain rate and sends an alert to my mobile phone so if need be I can shut the modem down remotely.

It does seem a bit odd though that it went straight to banding from non interleave :(

I wish I could give you some further advice re the REIN or SHINE issue,  but because by nature it is so hard to track down I don't think there really is that much more I can say about it other than what is on the REIN page.   The best thing you can do is what you are proposing and make sure its not something in your own premises. 
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kitz

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Re: BT DLM advice needed..
« Reply #38 on: October 02, 2019, 12:41:35 AM »

hmmmm  I thought I'd typed a reply to you a couple of days ago.   
I'd looked at and commented that the same bitload shape was there when on adsl which is a slightly surprising as vdsl and adsl use different PSD masks.

I'd waffled on a bit that Openreach uses something called dynamic spectral masks/management (DSM) for FTTC which are a sophisticated and more advanced way of controlling crosstalk between adsl & vdsl than the bog standard power cut back....  meaning even less likely that the shape would be from masks because they change depending upon.

1) How far your cab is from the exchange
2) How far you are from the cab

Sorry I mustn't have hit send properly.  :( :(  I know I was struggling to type as my hands are badly swollen and I cut the end bit short  after saying about how DSM adjusts on the fly also depending on local cross talk so you can even get different masks and power output the next time you sync and I was trying to decide just how much _real_ bandwidth that dip was costing you and never got around to looking up your headend exchange.   

I think I may have said something like

That same bitload shape is there despite vdsl masks being over extended tones.    In some respects the loss is less (percentage wise) with vdsl than adsl because vdsl has far more bit loading bins..  plus because PCB is harsher on FTTC on what are considered some of the adsl tones, then usually you lose less because those bins would never fully load anyhow even if the line was perfect.  and I was guestimating a couple of Mb at most and said it would likely to be less than what the interleaving was.
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kitz

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Re: BT DLM advice needed..
« Reply #39 on: October 02, 2019, 01:01:06 AM »

LCBAB is a parent (headend) exchange.

Quote
Parent
LCBAB   Bamber Bridge   Mounsey Road
      Bamber Bridge
      Preston
      LANCASHIRE
      PR5 6LT

Child
LCBAB   Bamber Bridge
LCHOG   Hoghton


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8062282

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Re: BT DLM advice needed..
« Reply #40 on: October 02, 2019, 07:07:30 AM »

1) How far your cab is from the exchange
2) How far you are from the cab



Sorry you're not well. I appreciate all the help that you & others are giving me. I just wish I knew more about all this network malarky.  I think I'm about 2km from the exchange & according to the OR engineer I'm about 300m from the cabinet. I've had a whinge to BT as I think the DLM was wrong in that it's just taken interleaving off in one foul swoop instead of at least halving it & then going from there. Will the banding ever come off or is that on for good now?


The DLM went to a interleave of 1 from 743. It re-synched again at 34,995. I unplugged the DSL cable for about 20 secs before I went to bed due to those millions of FECs (that was a week later though). I was worried it was going to create other errors during the night. The speed went up to 34,999 & that's where it's banded me at.
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kitz

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Re: BT DLM advice needed..
« Reply #41 on: October 02, 2019, 01:36:27 PM »

Sorry that wasn't an actual question it was explaining how the DSM shapes each individual bit load to try and prevent crosstalk with other lines.

vdsl DSM tries to give some protection for adsl, therefore if your cab is some distance from the exchange, it assumes (correctly) that any neighbouring lines on adsl will have a long length of copper, so it tries to protect and cut back tones most likely to be in use by the adsl users slightly more harshly than it would for any fttc users who are on a cab closer to the exchange.   Also if you live nearer the cab (irrespective of cab distance from exchange) then it will cut back power a little bit more than it does for those that live further away from the cab.    There's many different masks it can choose from PLUS it also tries to take into account any obvious signs of crosstalk that it would be impossible to say which DSM mask you had applied.   

What was apparent when comparing your adsl bit load to your vdsl bit load is that it had the same shape with very little (or no bits) loaded in exactly the same tones... thus I concluded that it wasn't just PSD masking but also some external noise which was lowering bit load over those tones.   
I can't recall the tone numbers now, but on vdsl there were some with zero which you perhaps would not expect for a line 300m from the cab irrespective of how far the cab is from the exchange.   I'm also ~300m from my cab and I have circa 10 bit load in tones in the same region. 

Everything appears to be pointing to the fact that noise is causing the issues for you and its followed you from adsl > vdsl.   Your physical line health (condition of the copper) appears to be good because the hlog is good, so Openreach doing a L&S is unlikely to make any difference. 

Whilst noise at those tones will impact your bandwidth availability less on vdsl than on adsl..   unfortunately the fttc DLM can be harsher than the one used by BTw for adsl..  therefore when your line is interleaved it can make quite a difference to what speed you sync at.     :(

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8062282

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Re: BT DLM advice needed..
« Reply #42 on: October 03, 2019, 07:49:51 PM »

Thanks Kitz - If I could speak as knowledgeably as yourself to these people it would make life easier. I still can't understand why the DLM would take interleaving off altogether & at the same time increase my speed to 39mb+ & drop the SNR 4.8. Why didn't it do it gradually instead of one foul swoop & create such a mess? Or is that how the DLM works? I don't do on-line gaming so the interleaving isn't an issue. The L & S was done when I was on copper & from my understanding that's just the copper lines from the exchange to the cabinet. No idea what was done if anything to the lines from the cabinet to the house. Can anything be done?  They flatly refuse to un-band me unless I agree to an engineer & accept the charges.  I don't dispute for a minute that my line can't handle much more speed, it's just frustrating to see the SNR going up at night to 7.5dB (approx) giving me an attainable of 45mb+ & I'm stuck at 35mb.  If only I could find what's keeping the speed down during the day...
« Last Edit: October 03, 2019, 08:27:47 PM by 8062282 »
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kitz

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Re: BT DLM advice needed..
« Reply #43 on: October 05, 2019, 12:02:30 AM »

Quote
I still can't understand why the DLM would take interleaving off altogether

New connections are put on Interleaving by default.   
If your line MTBE drops to ILQ green, then DLM removes interleaving (can't recall exactly how many err secs that converts to but its on the main site).

Quote
at the same time increase my speed to 39mb+

As mentioned in previous posts - interleaving and error correction carries overheads, these cost you some line speed.   When interleaving is removed most lines will see a decent increase in their sync speed.

Quote
& drop the SNR 4.8

That is nothing to do with DLM.   The ECI cabs have a target SNRM of 6.3 dB and nothing less than that - only the Huawei cabs have 'x'dB.   Therefore the 4.8dB must be attributable to noise on the line or one of your crosstalkers coming on line.
I suspect your line sync'd during a good period, but as the interference kicked in, this will be what caused your SNRM to decrease.

Quote
The L & S was done when I was on copper

It's my understanding that the term lift can be used to cover various scenarios...  but usually it is assigning you a new port at the exchange using the same copper run.   Line pair change is the term for changing the copper.   I've had a couple of what I'd deem line pair changes when I've had a fault in the past, yet I've seen on the report when it was swapped to a new pair at the UG JB right outside my house being reported back to the ISP as a L&S...  so who knows what they really changed on yours unless you saw what they did.:/

Quote
Can anything be done?

They could try a pair swap and hope you get an understanding engineer.   Your ammunition will be your DSLstats graphs showing the decreases and increases in SNRM.    You need to have a few days worth of SNRM graphs to show him so he can see the varience.    The varios Errors graphs will also be useful to show.

Quote
They flatly refuse to un-band me unless I agree to an engineer & accept the charges.

They 'should' be able to request a remote DLM reset at no cost to them.   It's not an automated process so not all ISPs like doing them.    As far as the engineer and charges, then that is a risk only you can decide on.

I took the risk, the engineer came out and did a pair change swap and wasn't charged.....  BUT I was told I'd been put on the last available pair which was only in slightly better physical condition than the one they changed it from despite the fact it sync'd at about 2Mb lower.   

I was told that as it was the final spare pair, then he wanted me to see how it ran for a couple of weeks and if the problem was still there, then Openreach  would need to pull a whole new length of cable through which was something he couldn't do.  Sounded reasonable so I said OK.    Two weeks later I re-reported it and was told nothing more could be done and that I was above the min threshold.   I feel I was a bit fobbed off by the attending engineer and have ended up with a line that syncs less than the old one...   however this one does have slightly less errors when  my daily error burst starts... so I guess as far as Openreach is concerned then it is the better line.

BlackSheep kindly checked the Openreach reports for me and couldn't see any mention of the pulling a new line to my premises, so perhaps I was fobbed off just to close the job, but he said he didn't think I'd get any further.   :/
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Black Sheep

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Re: BT DLM advice needed..
« Reply #44 on: October 05, 2019, 11:06:27 AM »

By way of an addendum .... you could indeed have a pair of wires that tests electrically better than another pair of wires, but depending on where that pair of wires is situated within the whole bundle, the X-Talk can trim away more synch than on the previous pair.

It's a juggling act for sure.  ;) ;D

 
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