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Author Topic: Modem Errors..  (Read 2005 times)

Weaver

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Re: Modem Errors..
« Reply #15 on: July 03, 2019, 05:08:15 PM »

Our user 8062282 asked:

Hi - Does DSLstats show all errors up, including the CRC/FEC errors etc that are below the SNR threshold?  I have an issue with noise at night but my ISP is claiming there is noise as well during the day. All I can see is an occasional spike and the CRC/ES/FEC errors are low.  If I didn't have the huge spike in errors at night, I'm almpost sure the DLM wouldn't keep reducing my speed.
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burakkucat

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Re: Modem Errors..
« Reply #16 on: July 03, 2019, 06:23:25 PM »

Hmm . . . I found a report for the above post, reply no. 14 (and promptly fixed it), before noticing that both roseway and Weaver had posted subsequently.
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kitz

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Re: Modem Errors..
« Reply #17 on: July 03, 2019, 07:12:39 PM »

Bit swap alone doesn't particularly prove anything.   It just tells us that your modem is working harder trying to keep bit rate sufficient to maintain sync.   Of more interest would likely be the SNRM graphs, as a reduction in SNR is usually what causes bit rate to drop.

I note from your last starts that the DLM has applied interleaving, which in itself will reduce the maximum attainable rate, but it should keep the errors under control. 

Quote
Does DSLstats show all errors up, including the CRC/FEC errors etc that are below the SNR threshold?

DSLstats will record all errors.  Check that you have the relevant boxes ticked under the Items to Monitor tab.
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ejs

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Re: Modem Errors..
« Reply #18 on: July 03, 2019, 08:11:07 PM »

Does DSLstats show all errors up, including the CRC/FEC errors etc that are below the SNR threshold?

The question does not make sense. There is no such "SNR threshold" for errors. Either the FEC data was used to correct something, or it wasn't. Likewise the CRC either matches the value calculated for the data received or it doesn't.
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8062282

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Re: Modem Errors..
« Reply #19 on: July 07, 2019, 06:59:58 AM »

I deleted this as I couldn't see any responses, apologies. 'Hi - Does DSLstats show all errors up, including the CRC/FEC errors etc that are below the SNR threshold?  I have an issue with noise at night but my ISP is claiming there is noise as well during the day. All I can see is an occasional spike and the CRC/ES/FEC errors are low.  If I didn't have the huge spike in errors at night, I'm almost sure the DLM wouldn't keep reducing my speed.'

The errors I can see during the day are minimal & using the DLM calculator, aren't anywhere sufficient to keep my speed down. TT just seem to be filling my head with rubbish & are extremely vague when responding & quite often don't answer the question at all.  Why can't I see this noise during the day?  Are TT telling porkies to keep me quiet.

I had the council out the other day to look at a street lamp outside my house as I thought it may have a faulty ballast. They've replaced the whole light fitting at the top. The 1st night afterwards, the errors didn't seem as high. The ES only went as high as 30 at points rather than the 45 before,
so I thought that might have been the issue.  Lo & behold in the early hours of Sat morning my SNR goes up to 16.6 & won't budge. The DLM then kicked in at 03.30 & the SNR stayed at 16.6. I've tried re-starting the router & switching it off for over half an hour.  With a SNR of 6dB my attainable is 8.5mb but my line rate is staying at 4095. Nobody on support at weekends & the tech peeps won't just optimise the line for you without having you jump through hoops.

Whilst the SNR is at 16.6, it's not showing up any errors, hence my question about DSLstats showing all errors. When the SNR is at 6dB, DSLstats shows significantly more errors. Below is the worst day in the last week..

Average error rates for 02 Jul 2019

CRC erors per hour:  46.1 Down,  0.38 Up
FEC erors per hour:  229 Down,  6.75 Up
HEC erors per hour:  400 Down,  0.21 Up
ES per hour:  12.3 Down,  0.25 Up
SES per hour:  0 Down,  0 Up

I have all the tick boxes checked. I'm new to monitoring my connection so apologies if I sound a bit dim  :)   
« Last Edit: July 07, 2019, 07:51:24 AM by 8062282 »
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8062282

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Re: Modem Errors..
« Reply #20 on: July 07, 2019, 07:50:04 AM »

Did you mean to post that in an impossibly small font? Here it is in normal size:

"Hi - Does DSLstats show all errors up, including the CRC/FEC errors etc that are below the SNR threshold?  I have an issue with noise at night but my ISP is claiming there is noise as well during the day. All I can see is an occasional spike and the CRC/ES/FEC errors are low.  If I didn't have the huge spike in errors at night, I'm almost sure the DLM wouldn't keep reducing my speed."

Apologies, that was posted from my iPhone. No idea why it came out that size, sorry..
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Chrysalis

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Re: Modem Errors..
« Reply #21 on: July 07, 2019, 07:59:49 AM »

im not convinced this is due to DLM, could easily be variable line conditions, if it ever syncs at 8mbit again please grab the line stats
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8062282

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Re: Modem Errors..
« Reply #22 on: July 07, 2019, 10:15:31 AM »

This is what the Billion 7800DXL is reporting at 6dB
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kitz

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Re: Modem Errors..
« Reply #23 on: July 08, 2019, 11:27:03 AM »

Bit swap alone doesn't particularly prove anything.   It just tells us that your modem is working harder trying to keep bit rate sufficient to maintain sync.   Of more interest would likely be the SNRM graphs, as a reduction in SNR is usually what causes bit rate to drop.

The SNRM is usually the most important graph to monitor when it comes to trying to understand what is happening to the line.   It can show if the line is suffering from regular night time patterns or if they are quick noise spikes.   I notice you mention getting the council out to the street light.   If it was the street lamp then you would normally expect the SNRM to dip by a few dB at dusk and the SNRM to increase again at dawn corresponding to when the light comes on and goes off.   Use the SNRM graphs over a period of time to see if you can see regular patterns occurring.  Dips in SNR(m) is what usually causes bitswap and errors to increase.

The DLM doesn't look at night and day independently, but takes into account what has happened over the course of the full 24hr period.    Therefore as far as it's concerned if you are breaching the error threshold at night, (even if it is just at night) it will class the line as having breached the full days limit and take action accordingly. 

 
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8062282

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Re: Modem Errors..
« Reply #24 on: July 08, 2019, 05:24:08 PM »

Hi - Thanks for getting back to me. The SNRM doesn't really fluctuate that much at night. It probably fluctuates by 0.1 up to 0.3 of a dB at night. I've attached a SRNM graph of the 7th showing it to bit a bit wobbly & then about 3ish it shoots up to 16dB & then for the next two nights, there was no errors showing up at all. Hence my previous question about DSLstats showing up all errors irrespective of the SNR. Rebooting the router or switching it off for half an hour wouldn't budge the SNR.   TT optimised the line this morning & the line synced at 7.9Mb. DLM kicked in later that morning & my speed went back down to 3511.

The council changed the light fitting Friday morning & the ES errors didn't seem as high Sat morning when I checked. Unfortunately when the SNR shot up to 16, DSLstats didn't report any errors for the following 2 nights. I've just re-started the router & the speed has increased to 4165 with a SNR of 6dB. I will have to see what errors it reports tonight.

What I'm trying to get my head round is, why are such low errors causing a performance issue. I had an engineer out on the 14th of June as the SNR started to swing about all over the place causing disconnections etc. He did some work in the cabinet & changed the D & E round. That stopped the SNR swinging about but hasn't stopped all the ES at night nor has it stopped the DLM keep reducing my speed. The average ES for the previous 7 days is 125 with low CRC/FEC errors. Mostly accumulated between 22.30 & 05.30. I don't think that amount of errors should be an issue for DLM.   TT are a complete waste of time & just keep avoiding the issue.

I've tried 2 different modems, different filters, invested in a nice new solid copper RJ11 to RJ11 cable but nothing is stopping the problems. I want to move to fibre but I don't want the issue to cause me any problems, as I know you can't have the DLM reset like you can on ADSL.  All I can do is try to get to the bottom of it or hope that the problem is between the exchange & my cabinet.

Despite the SNR staying fairly constant up to 3am, the ES were going up till they dropped off about 4ish. No idea what the upstream ES was earlier. That was just a random one...
« Last Edit: July 08, 2019, 05:57:52 PM by 8062282 »
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kitz

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Re: Modem Errors..
« Reply #25 on: July 09, 2019, 07:13:55 AM »

OK its kind of obvious now why you asked the question which didn't make sense.

Firstly DSLstats will record all errors, the reason why none were recorded after the SNRM shot up to 16dB is simply because there weren't any.

SNR Margin is a buffer zone above the true SNR.  The higher the SNR Margin, then the less likely there is to be any errors.   SNRM and Target SNRM is a way the DLM can help to stabilise a line.  The downside for you is by increasing the Target SNRM, this takes away a large chunk of sync speed.

Have a read of:
~ What is SNR?
~ What is SNR Margin?
~ What is Target SNR Margin (TNMR)?
and you will perhaps understand why the DLM is using the Target SNRM on your line.



The big question now is what is triggering the DLM to increase the Target SNRM?

There are 2 main parameters which the DLM monitors to decide if it needs to take any action
1) The amount of Errored Seconds
2) The number of line retrains  (resyncs)

Looking at your line stats ~125 Err Seconds should not trigger the DLM and if you can confirm that the line didn't have a lot of disconnections the previous day then it becomes a bit puzzling why it should behave the way it is doing. 

One possibility that does spring to mind - especially when your target SNRM appears to shoot straight up to ~15dB - is that TT have you on a very harsh DLM profile.   There are many different profiles that TT use, but from memory 15dB is one of their maximum stability profiles.


I'm wondering if your DLM profile is too agressive.  - No matter how many times TT reset the DLM, if the actual profile is too high, then DLM could literally be kicking in just after a low rate of errors.

Try asking TT what your DLM profile is and can it be reduced.   
The profile will look something like SF_15_24M_1M.   With me not being on TT I'm not sure offhand what options are available to you, but try asking if your DLM profile can be changed to a lesser one now that the line fault has been fixed by the engineer to one of the 6dB profiles.    Perhaps b*cat can recall which profile he is on?
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8062282

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Re: Modem Errors..
« Reply #26 on: July 09, 2019, 06:05:04 PM »

Hi Kitz - I had a period of 2/3 days where the SNR was up & down & going into the minus with the odd disconnect. This prompted me to get the engineer out on the 14th June. After he changed the D & E the SNR has been rock solid & has never really deviated from 6dB. The BTOR engineer also told me he had to get TT to take a cap off my line which TT denied was on there. The SNR dips a little at night but after googling for info, that's the norm. Apart from those disconnects, I never get any disconnects at all. The only time I get a disconnect is when the DLM kicks in.

I can't actually get TT to tell me what profile I'm on. I've asked numerous times & they just evade the question. None of what they're saying correlates with what the stats are showing. Now they've reset the DLM Monday morning, the ES that I'm worried about are now showing up. It seems like the street lamp that I thought was the problem, isn't the problem. I've attached a pic. TT aren't interested. When all these errors are occurring, there's no movement in the SNR. I've attached a pic of the SNR covering most of that period. I haven't seen a dip like that in the upstream before, that's a new one.

Today I have 2 steep downward SNR drops on the upstream & one downstream dip that caused a disconnect. You can see one of the upstream dips & the downstream dip in the attached pic. That's never happened before in all the time I've been monitoring my connection. Not sure what caused that.

As today hasn't yet finished, here's my average errors for yesterday. These surely can't be enough for the DLM to keep kicking in and reducing my speed or are they? Most of the errors have been accumulated during the period where I get all the ES at night. We live in a quiet avenue. I'm in bed for 10.15 as I'm up at 5.30 so it's not like there's anything on in the house at that time which would cause those errors.


Average error rates for 08 Jul 2019

CRC erors per hour:  43.6 Down,  0.58 Up
FEC erors per hour:  292 Down,  1.38 Up
HEC erors per hour:  75.9 Down,  0.63 Up
ES per hour:  3.71 Down,  0.50 Up
SES per hour:  0.46 Down,  0 Up

I will try asking for my profile again & see what they come back with. Can I demand to know what profile I'm on?

Thanks for your help & I will have a read of those links you sent. I've been googling for info all over the place & none of what TT are saying is making sense compared to what the stats are showing me. They keep telling me I have excessive noise during the day, not just at night. That would show up in the stats wouldn't it?  My errors during the day are minimal compared to those accumulated at night.
« Last Edit: July 09, 2019, 07:00:17 PM by 8062282 »
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burakkucat

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Re: Modem Errors..
« Reply #27 on: July 09, 2019, 10:51:07 PM »

Perhaps b*cat can recall which profile he is on?

I can't say in TT-speak but in the ordinary words that we would use my circuit is provisioned with a DLM Off, target SNRM 6dB and interleaved profile.
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8062282

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Re: Modem Errors..
« Reply #28 on: July 10, 2019, 06:58:45 PM »

Hi - TT did tell me my profile. The one Kitz thought it might be was their old system. My profile is 4096_1024_M6 (interleaved). I'm supposed to be on an 8mb line but it appears I'm capped at 4mb, They said my line isn't stable at higher speeds.  They keep going on about 'instability caused by the fluctuating background noise'.  My modem is connected to the master socket & I have a MK3 filtered face plate on there.  If there was noise, would this not make my SNR go down & how would I see the noise in DSLstats?   It's only started going up to 16dB in the early hours of the morning, since weekend. When it does that, I don't see any errors at all. The only way to get it back down to 6dB is to get them to optimise the line. This sorta defeats the training period if it keeps going up to 16dB. I will see what happens tonight.  Before that the SNR was always stable at 6dB.

Is any line completely error free? This is my error count for yesterday. Is that enough for the DLM to keep my speed down


Average error rates for 09 Jul 2019

CRC erors per hour:  39.3 Down,  11.9 Up
FEC erors per hour:  539 Down,  35.0 Up
HEC erors per hour:  271 Down,  88.1 Up
ES per hour:  10.8 Down,  1.54 Up
SES per hour:  0.83 Down,  0.17 Up

So far today


Average error rates for 10 Jul 2019


CRC erors per hour:  34.1 Down,  0.36 Up
FEC erors per hour:  429 Down,  1.58 Up
HEC erors per hour:  172 Down,  0.18 Up
ES per hour:  5.33 Down,  0.24 Up
SES per hour:  1.21 Down,  0 Up

They've had me disconnect everything for 2 hours tonight while they run some tests. I'll find out what the result is tomorrow.


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kitz

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Re: Modem Errors..
« Reply #29 on: July 10, 2019, 09:04:20 PM »

5.33 E/S per hour (128 per day) is nothing...  although with a 15/16dB SNRM you wouldn't be expecting to receive many as the large margin would stop many from occurring in the first place - as would interleaving 

>> If there was noise, would this not make my SNR go down

Yes it would.   
If it were me, I would temp adjust the graph period to 24hrs and send them some screen shots over the course of a few days showing them how stable the SNRM is. 

(Change graph view from Configuration > Graphs > Time per page.)

I'm afraid I am not aufait with what their LLU DSLAM does these days - but the reps on their own forum used to be far more efficient at amending a line profile than going through their CS support desk.
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