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Author Topic: BT DLM advice needed..  (Read 5357 times)

8062282

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BT DLM advice needed..
« on: September 21, 2019, 07:07:13 AM »

Hi - Was on TalkTalk for quite a while & my line deteriorated. Had many issues & it was almost impossible to get them to resolve the issue. I did have an engineer out & that didn't solve the issue of noise & the SNR fluctuating. My cabinet opened up for FTTC so I moved to BT. An OR engineer came & did a lift & shift. My top speed on a clean line prior to the L & S was 54.8 & the low was 52.9. After the L & S that's dropped to 52.1 & 50.3. Not a huge difference but I'm disappointed that I've been banded at 40/10. BT went to change me onto a 55/10 but said the option wasn't there. Apart from a few thousand FECs, error count was low & has been for the past 10 days. I still have a a noisy line & the SNR is still going up at night & then dropping during the day. When the SNR goes up the attainable rate is 45/46Mbs. SNR at some point during the day drops to 6dB. On the 21st the SNR went up to 7.8dB for about an hour & then dropped to 7.3dB. The change created a 1200 US error second spike & the errors are continuing. SNR has dropped to 4.8dB & the interleave has dropped from 693 to 1. Error count for yesterday which included two 1200 US ES spikes..

Average error rates for 20 Sep 2019
CRC erors per hour:  376 Down,  1.38 Up
FEC erors per hour:  125 Down,  7.55 Up
HEC erors per hour:  884 Down,  0 Up
ES per hour:         32.6 Down,  100 Up
SES per hour:        1.50 Down,  0.33 Up
Total ES in the day: 780 Down, 2397 Up.


The 2nd 1200 ES spike was me unplugging the DSL cable from the back of the modem for about 20 secs to try & stop the errors. The odd thing is, FECs have always been an issue despite low errors in other area's. Now the FECs on the DS have stopped altogether. All the other errors are increasing. Error count from midnight today:

Average error rates for 21 Sep 2019


CRC erors per hour:  430 Down,  1.38 Up
FEC erors per hour:  0 Down,  2.30 Up
HEC erors per hour:  194 Down,  0 Up
ES per hour:         31.2 Down,  1.38 Up
SES per hour:        1.38 Down,  0 Up
Total ES in the day: 204 Down, 9 Up


I've attached a screen shot showing the ES, bit loading graph & the QLN.  I also have some different stats being reported in the modem to what DSLstats is reporting. The stats are telling me:



Max:    Upstream rate = 8204 Kbps, Downstream rate = 38029 Kbps
Bearer: 0, Upstream rate = 8024 Kbps, Downstream rate = 39973 Kbps


My modem is telling me:



VDSL Port Details       Upstream         Downstream
               Line Rate:      8.044 Mbps       40.035 Mbps
Actual Net Data Rate:    8.024 Mbps       39.973 Mbps


BT aren't going to do anything as I'm getting the above the guaranteed speed. Surely this isn't normal or is it? No idea how BT DLM works & whether it'll think these errors are acceptable day in day out. I did consider a re-boot last night due to the different stats in the modem & DSLstats, but I thought I'd wait to see if DLM kicked in this morning. It hasn't.



Stats recorded 21 Sep 2019 07:06:26


DSLAM type / SW version:   IFTN:0xd086 (208.134) / v0xd086
Modem/router firmware:     AnnexA version - A2pv6F039v.d26a
DSL mode:                  VDSL2 Profile 17a
Status:                    Showtime
Uptime:                     17 hours 51 min 18 sec
Resyncs:                   2 (since 19 Sep 2019 06:08:54)
         
            Downstream   Upstream
Line attenuation (dB):     19.8      0.0
Signal attenuation (dB):   Not available on VDSL2     
Connection speed (kbps):   39973      8024
SNR margin (dB):           4.8      6.1
Power (dBm):               12.2      6.0
Interleave depth:          1      1
INP:                       0      0
G.INP:                     Not enabled      Not enabled
Vectoring status:          5 (VECT_UNCONFIGURED)     


RSCorr/RS (%):             N/A      0.0066
RSUnCorr/RS (%):           N/A      0.0000
ES/hour:                   30.1      1.27

Let me know if you need anything else from DSLstats.  Any advice? 


EDIT (21.09.18 07.53) - The modem has just re-synched which has resulted in the SNR going from 4.8dB to 7.1dB & the speed has dropped.  Interleave is still at 1 / 1. G.INP isn't on. Still no FEC errors but all the other errors are still there & increasing. Seems very odd to that's it's started doing this..



Max:    Upstream rate = 8184 Kbps, Downstream rate = 37824 Kbps
Bearer: 0, Upstream rate = 7968 Kbps, Downstream rate = 34974 Kbps

« Last Edit: September 21, 2019, 07:58:46 AM by 8062282 »
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ejs

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Re: BT DLM advice needed..
« Reply #1 on: September 21, 2019, 09:04:13 AM »

I don't see any particular problem here. The error rate looks perfectly acceptable. There'll be no FEC count on the downstream because there isn't any FEC applied to the downstream. Are you experiencing any problems with your usage of the Internet? It sounds like that at some point, interleaving and FEC were switched off, and subsequently your error rate became higher, which is entirely to be expected.
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8062282

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Re: BT DLM advice needed..
« Reply #2 on: September 21, 2019, 09:28:53 AM »

I don't see any particular problem here. The error rate looks perfectly acceptable. There'll be no FEC count on the downstream because there isn't any FEC applied to the downstream. Are you experiencing any problems with your usage of the Internet? It sounds like that at some point, interleaving and FEC were switched off, and subsequently your error rate became higher, which is entirely to be expected.


It just seems odd that I've had a low error count for days (apart from FECs) & then all of a sudden the speed drops & the error count starts going up & up. I've always had 1000's FEC errors. Does a 1200 upstream ES spike sound normal when the modem re-syncs? I'm not sure what you mean by 'there isn't any FEC applied to the downstream'.


The issues that I had with TalkTalk seem to be ongoing with BT in that my line doesn't seem very stable & seems to doing odd things sporadically. I should have gone onto VDSL on the 6th Aug but OR migrated me to copper in error. The OR engineer (10th Aug) did the L & S when I was on BT ADSL. I thought that was a bit pointless as I didn't migrate to BT VDSL until the 22nd.  I'm just wondering if I could persuade them to get an engineer out now I'm actually on the right service..


Thanks for the info on the errors. I'm not sure what the BT DLM considers acceptable..
« Last Edit: September 21, 2019, 09:39:44 AM by 8062282 »
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ejs

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Re: BT DLM advice needed..
« Reply #3 on: September 21, 2019, 09:50:03 AM »

I'm not sure what you mean by a 1200 upstream ES spike. That's 20 minutes of constant ES. I can't really see how you can actually have 1200 ES in any shorter space of time. If your stats have 1200 ES in an instant spike, that'll be some sort of reporting oddity during the re-sync.

When you had interleaving, you had forward error correction on the downstream. Now you have no error correction on the downstream.

I think the DLM limit is 2880 ES per day for the Openreach Speed profile (which equates to the MTBE red threshold of 30).
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8062282

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Re: BT DLM advice needed..
« Reply #4 on: September 21, 2019, 10:56:51 AM »

I'm not sure what you mean by a 1200 upstream ES spike. That's 20 minutes of constant ES. I can't really see how you can actually have 1200 ES in any shorter space of time. If your stats have 1200 ES in an instant spike, that'll be some sort of reporting oddity during the re-sync.

When you had interleaving, you had forward error correction on the downstream. Now you have no error correction on the downstream.

I think the DLM limit is 2880 ES per day for the Openreach Speed profile (which equates to the MTBE red threshold of 30).


I'm on my 3rd modem. I had a billion 7800DXL on ADSL & continued to use that when I was on BT ADSL. I them got a VMG3925-10B & now I'm using a VMG8924-B10A. All 3 have at some point indicated a weird US error second spike. If it shows in my modem stats, is this being reported back to the DLM?  After always seeing 1000's of FEC errors on the downstream, it's a surprise not to see any at all. I never really had any CRC's but now I'm getting lots of CRC's. I would prefer FECs to CRCs.


After being on BT since the 22nd, my speed & errors are the worst they've been since the re-sync at midnight on the 20th Sept.  I suppose I'm stuck with what I have as I'm above the guaranteed speed. I did say that the line they gave me after the L & S was worse (in terms of speed) than I had before but they aren't bothered. I also find it a bit frustrating that somebody who's on the same cabinet as me can get 55/10 & I'm banded at 40/10 because of a poor line. Especially when you pay the same. I used to have good internet & then it suddenly went very poor & that's when all the issues started. I suspect over time, my line has been swapped. Rob Peter to pay Paul. As I haven't been on VDSL before, I have nothing to compare it too.
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kitz

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Re: BT DLM advice needed..
« Reply #5 on: September 21, 2019, 07:36:54 PM »

Quote
I also have some different stats being reported in the modem to what DSLstats is reporting.

DSLstats gets the figures via telnet from the Broadcom CLI (modem chipset)
The sync rates are actually the same - Just the labelling is different.

DSLstats --- >  Bearer: 0, Upstream rate = 8024 Kbps, Downstream rate = 39973 Kbps
Web GUI ---->  Actual Net Data Rate:    8.024 Mbps       39.973 Mbps


The other 2 figures are the max attainable rate and can vary by the second depending upon your SNR Margin.   It is an estimated figure based on various factors and should not be relied upon especially if interleaving is involved


--------------

The presence of FECs [usually] mean that you have Interleaving and RS error correction switched on.   The fact that you no longer are getting any FECs means that the DLM has judged your line stable enough to attempt running the line without error correction.   

The fact DLM has switched off Interleaving & error correction is usually a good sign that all is OK with the line and it is performing within acceptable parameters.
 
It is perfectly normal for a line without error correction to see an increase in CRCs. Have a read of the Error Correction page - in particular the bit about FEC and Reed Solomon Coding.   But in a nutshell FECs are what could become CRCs if the line wasn't interleaved.

As long as your line is performing within its profile then up to 2880 E/Secs per day for speed profile is considered acceptable by DLM.    Most lines will record a few additional errors during the sync process.

You won't get G.INP as you are on an ECI cab.   Most lines see a better sync speed when 'Interleave' is switched off because you don't have RS overheads.


----

Quote
I'm banded at 40/10 because of a poor line.

You are not banded in the true sense.  Whilst I appreciate that BT are restricting you to the 40Mbps product, from what I can see there just is not any more speed availability in that line.

More of interest would be looking at your SNR Margin graphs to determine if there is a pattern to the SNRM fluctuations.

[Moderator edited to replace a space character that "got away".]
« Last Edit: September 21, 2019, 08:28:35 PM by burakkucat »
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j0hn

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Re: BT DLM advice needed..
« Reply #6 on: September 21, 2019, 11:34:27 PM »

BT are likely using the Speed DLM policy and Talktalk always use Standard so it's not a huge surprise the line runs fastpath instead of Interleaved after the switch.

DLM allows twice as many ES in such a case and what DLM policy an ISP uses would be high on my priorities list, especially if I were still on an ECI DSLAM.
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8062282

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Re: BT DLM advice needed..
« Reply #7 on: September 22, 2019, 11:45:58 AM »

Hi - Thanks for replies, Kitz & jOhn. The internet dropped connection last night & DSLstats threw a wobbler sometime in the night, When I checked it this morning, it came up with a floating decimal point error & stopped recording. I had to close it & re-start it.


Anyway, the DLM kicked in last night & I'm back to interleaving on at 793 on the DS. SNR is a 6.3dB. Speed has dropped to 34,995 with an attainable of 41,727. My errors prior to DSLstats having a dicky fit were.

Average error rates for 21 Sep 2019


CRC erors per hour:  477 Down,  1.45 Up
FEC erors per hour:  0 Down,  2.17 Up
HEC erors per hour:  180 Down,  0 Up
ES per hour:         32.7 Down,  148 Up
SES per hour:        2.53 Down,  0.48 Up
Total ES in the day: 2169 Down, 2473 Up


Looking at the log, it stopping recording at 23.06 so I guess those figures aren't too far out. I've been on VDSL since the 22nd of Aug & even now, my line isn't stable in that, it's unpredictable. They've banded me on a 40/10 despite my speeds being 52.1 & 50.3 on the DSL checker. Prior to the L & S there were 54.8 & 52.9. I have this issue which came with me from TalkTalk in that the noise drops at night sometimes so much that the SNR goes up giving me an attainable speed of 45/46Mb. When I first went onto VDSL, they put me on ADSL in error (6th Aug) & I didn't go over to VDSL until the 22nd. They addressed the drops & noise whilst I was on ADSL, hence the L & S & I lost a couple of MB on the DSL Checker. No big deal, it's just the unpredictable line means the DLM is up & down like a yo yo. I just wish the OR engineer had said there was no point in sorting this line out until I was on VDSL.


Even though I'm above the guaranteed speed (a paltry 25mb), is it worth reporting this fluctuating SNR & will they do anything about it?  How do they arrive at the guaranteed speed? I'm about 300m from the cabinet.  No idea if my speed will go back to the 39Mb I had previously or will this constant up & down SNR end up with me being banded at my current speed of 35Mb. Why also, is somebody expected to pay the same if they're banded at 40/10 & somebody on the same cabinet roughly the same distance can get 55/10. I know I sound like a spoiled brat over a few MB's but this unpredictable line is a tad frustrating. OR, instead of improving my line, have made it worse, in that, I have the same issues & I've lost speed at the top end. BT should at least take ownership of that..



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Weaver

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Re: BT DLM advice needed..
« Reply #8 on: September 22, 2019, 01:45:17 PM »

> I know I sound like a spoiled brat over a few MB's

You are.  ;)   But youíre not alone!  :)   Itís the same as me moaning all the tied over my wretched upstream combined speed bonding efficiency and some linesí varying upstream.

This might help soothe you.
Live sync rates:
  #1: down 2913 kbps, up 532 kbps
  #2: down 2762 kbps, up 512 kbps
  #3: down 2748 kbps, up 352 kbps
  #4: down 2850 kbps, up 496 kbps

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8062282

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Re: BT DLM advice needed..
« Reply #9 on: September 22, 2019, 02:52:30 PM »

@Weaver - Bless. I was in you shoes when I was with TalkTalk, my download was 1595 when I first measured it. A guy just posted on the BT forum & he only gets 448kb download. He lives in the sticks though :)


I had a good internet connection when I was with Virgin. 8mb line with a 6.5mb download over wi-fi. I then got 'dumped' on TalkTalk when Virgin didn't want to support their ADSL customers anymore. I was still getting a 6.5mb download so all was good. Round about the beginning of the year my internet started getting slower & slower. Being naive & not knowing what to do for the best, I'd re-boot the router in the hope I'd get a better speed. I did, albeit it was short lived. Come March, I'd had a enough & that's when I posted on the TalkTalk forum & that's when I started learning about the do's & don'ts. I also learned how unhelpful TalkTalk were & their rubbish aggressive DLM. When the SNR went up at night, the attainable was 9.5mb but due to their rubbish DLM, I never got anyway close to that. In the end, I was capped at 4mb.


When I got put on ADSL in error & they did a lift & shift, I pointed out that my line was worse than it was before. All everybody kept saying was, wait until you're on VDSL & everything will be alright. Now I'm on VDSL & everything isn't alright, I'm expected to live with it because I'm getting above the guaranteed speed. OR had the opportunity to put me on a better line & for whatever reason, they gave me a worse one. I say worse in that I've lost top end speed. One thing that has stopped is some night time error seconds that TalkTalks DLM took great delight in using to reduce my speed. I don't get those on VDSL so the L & S did cure one issue. I'm still getting the fluctuating SNR, although it doesn't go as high as it did when I was on TalkTalk. 7.8db is the highest on BT, on TT it was going into double figures..


Just for giggles I've attached a picture of my cabinet. I'm 300m away. The garage behind it including the Spar to the right & the used car garage & the house to the left have all been demolished. It's just a cordoned off area of stones. They could have upset anything demolishing everything (maybe). There's a street lamp that sits about 2' from the cabinet + two redundant lights for the garage + 2 sets of traffic lights. Any one of many things that could be causing an issue..

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gt94sss2

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Re: BT DLM advice needed..
« Reply #10 on: September 22, 2019, 05:53:35 PM »

I would ignore the errors if I was you for the timebeing - and post a screenshot of the SNR graph over 24 hours. That is likely to be more informative about the quality of your line - and if you do it over a period of several days, their may be a clue as to what is causing your SNR to vary.

FEC errors are not really errors but errors that the modem has prevented.

Modems which are interleaved generally show overly optimistic/unachievable  maximum attainable data rates.

Whatever, you do - don't reboot or disconnect the modem.. - that will just make DLM think your line is unstable
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8062282

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Re: BT DLM advice needed..
« Reply #11 on: September 22, 2019, 06:52:34 PM »

I would ignore the errors if I was you for the timebeing - and post a screenshot of the SNR graph over 24 hours. That is likely to be more informative about the quality of your line - and if you do it over a period of several days, their may be a clue as to what is causing your SNR to vary.

FEC errors are not really errors but errors that the modem has prevented.

Modems which are interleaved generally show overly optimistic/unachievable  maximum attainable data rates.

Whatever, you do - don't reboot or disconnect the modem.. - that will just make DLM think your line is unstable


Hi - I've been monitoring my connection since sometime in June. The SNR is always quite stable. It deviates maybe 0.2 at most, up or down. Suddenly it will go up late at night or very early hours of the morning. It can stay like that until morning or as late as lunch-time & then it goes down to 6. something. I can be sat here on my own using nothing in the house other than the PC & all of a sudden it will go back down. There's usually a spike of something that presumably creates enough noise to bring it back down. It's not anything we switch on or off in the house as I've seen it happen often enough when I'm on my own. Whilst I'm at work, if I see any unusual spikes of interference that have happened during the day, when I get home, my partner get the the 3rd degree about what they've used & at what times :)   


I did get excited about going onto VDSL as there's a green cabinet 20' away. I then got very un-excited when OR told me it was a Virgin cabinet. I did see another cabinet at the bottom of the avenue, maybe 150m away. My cabinet is up on the other side of the road on the main road through where I live about 300m away. Can't tell whether the one at the bottom of the avenue is a BT cabinet though. I've posted a pic. If it's a BT cabinet, I would imagine I'd have to donate a kidney to get my line swapped to that :)


I never randomly re-boot the router. If I've switched it off as I did when I made a bespoke Cat 6 RJ11 - RJ45 cable up, I've always left it off for at least 30 mins..
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j0hn

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Re: BT DLM advice needed..
« Reply #12 on: September 22, 2019, 07:02:09 PM »

You're line didn't look banded at 40/10 in the first post.
In the stats you showed above it was below 40Mb and the attainable showed it wasn't capable of going that high.

It might have 1 day but crosstalk eats away at the speeds of most lines over time.
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8062282

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Re: BT DLM advice needed..
« Reply #13 on: September 22, 2019, 07:29:26 PM »

You're line didn't look banded at 40/10 in the first post.
In the stats you showed above it was below 40Mb and the attainable showed it wasn't capable of going that high.

It might have 1 day but crosstalk eats away at the speeds of most lines over time.


It was sat quite happily at 39.5mb until this morning when it all went pear shaped. When interleaving came off on the 20th that's when the errors started getting really high. When it re-synced to 34.995 this morning the errors have been negligible all day. Looking at the wi-fi connections there's a lot of FTTP so maybe one day things will improve. Not sure how I'll find out though if I'm banded at 40/10.
« Last Edit: September 22, 2019, 07:59:57 PM by 8062282 »
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burakkucat

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Re: BT DLM advice needed..
« Reply #14 on: September 22, 2019, 07:53:56 PM »

Can't tell whether the one at the bottom of the avenue is a BT cabinet though. I've posted a pic.

I can confirm that it is not part of BT's or Openreach's infrastructure.
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