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Standard User milesharrison
(newbie) Sun 27-Dec-20 02:10:34
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Flaky FTTC and frequent dropouts


[link to this post]
 
Visiting my mums over xmas (don't panic, it's all officially sanctioned!), the internet has slowly been getting worse and worse. It's quite a large house so I put in a mesh wifi system and hoped that would help affairs. It has fixed the wifi but was still having serious reliability issues and slowdowns.

Changed VDSL modem to a known good one (a Zyxel and also a Draytek which are both mine, end up getting a similar line rate) but the issues remain. We've always had an issue with water ingress into the phone line so that is probably the most likely culprit but really, we need BT to replace the line from the mast as every time they 'fix' it, problems promptly return. I took the (5-10 year old) master socket and most of the pins were corroded with water damage. Replaced it with a brand new (5c) and still get about the same line rate. There are NO wired extensions connected as I removed them all some years ago and it is just the house phone and the modem that are connected to the master socket.

When I last lived here, it would sync at ~55mbit and now can't get it beyond 33. The symptoms of the internet issues are total connection drops (following 500 or so CRC errors as shown below). That's the simple one. The other issue that I cant narrow down is just poor performance. Speedtests will drop to 10mbit for a short period (5-10 mins) and occasionally, sites will just stop loading but it recovers itself sometimes without retraining the connection. Stats are below for my Zyxel VMG1312-B10A.
VDSL Training Status: Showtime
Mode: VDSL2 Annex B
VDSL Profile: Profile 17a
G.Vector: Disable
Traffic Type: PTM Mode
Link Uptime: 0 day: 0 hour: 2 minutes
====================================================================================
VDSL Port Details Upstream Downstream
Line Rate: 8.418 Mbps 29.998 Mbps
Actual Net Data Rate: 8.419 Mbps 29.999 Mbps
Trellis Coding: ON ON
SNR Margin: 6.3 dB 10.4 dB
Actual Delay: 0 ms 0 ms
Transmit Power: 4.4 dBm 12.5 dBm
Receive Power: -9.2 dBm -15.0 dBm
Actual INP: 44.0 symbols 54.0 symbols
Total Attenuation: 0.0 dB 23.0 dB
Attainable Net Data Rate: 8.419 Mbps 40.911 Mbps
====================================================================================
VDSL Band Status U0 U1 U2 U3 U4 D1 D2 D3
Line Attenuation(dB): 9.2 40.3 59.2 N/A N/A 17.7 47.7 73.9
Signal Attenuation(dB): 9.2 39.8 58.6 N/A N/A 25.7 47.3 76.8
SNR Margin(dB): 6.7 6.3 6.3 N/A N/A 10.4 10.4 10.4
TX Power(dBm): -0.1 -2.5 0.3 N/A N/A 10.6 7.7 -4.6
====================================================================================

VDSL Counters

Downstream Upstream
Since Link time = 2 min 19 sec
FEC: 13 0
CRC: 0 0
ES: 0 0
SES: 0 0
UAS: 0 0
LOS: 0 0
LOF: 0 0
LOM: 0 0
Latest 15 minutes time = 14 min 18 sec
FEC: 2275 0
CRC: 575 0 ********** Shortly before the connection drop/retrain
ES: 11 0
SES: 11 0
UAS: 38 27
LOS: 1 0
LOF: 7 0
LOM: 0 0
Previous 15 minutes time = 15 min 0 sec
FEC: 52 0
CRC: 0 0
ES: 0 0
SES: 0 0
UAS: 0 0
LOS: 0 0
LOF: 0 0
LOM: 0 0
Latest 1 day time = 22 hours 59 min 18 sec
FEC: 11241 7
CRC: 575 5
ES: 11 5
SES: 11 0
UAS: 66 55
LOS: 1 0
LOF: 7 0
LOM: 0 0
Previous 1 day time = 0 sec
FEC: 0 0
CRC: 0 0
ES: 0 0
SES: 0 0
UAS: 0 0
LOS: 0 0
LOF: 0 0
LOM: 0 0
Total time = 22 hours 59 min 18 sec
FEC: 11241 7
CRC: 575 5
ES: 11 5
SES: 11 0
UAS: 66 55
LOS: 1 0
LOF: 7 0


Wondering how to persue it, hopefully some here will come up with some good suggestions. Again, I imagine the only real solution would be to replace the line, but I imagine it will be very hard to convince BT to do that. The point where the phone line enters the house has been changed 3 times over the last 25 years due to water ingress and subsidence.

Cheers in advance!
Standard User Zarjaz
(eat-sleep-adslguide) Sun 27-Dec-20 06:54:34
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Re: Flaky FTTC and frequent dropouts


[re: milesharrison] [link to this post]
 
Is the line free from audible noise ?

Have actually reported the broadband issue to the service provider, that would be my first step.

Standard User j0hn83
(fountain of knowledge) Sun 27-Dec-20 13:53:40
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Re: Flaky FTTC and frequent dropouts


[re: milesharrison] [link to this post]
 
The downstream has been capped/banded by the DLM.
It won't/can't sync above 30Mb/s (29.999) unless the DLM is reset or the line remains very stable and the DLM removes the cap.

Banding is usually caused by too many resyncs in a short time period.
This could be because of OpenReach working on the cabinet, a line fault, or your mum rebooting the Hub over and over.

Going by the stats the line should be syncing around 40Mb instead of the 30Mb it is capped to.

If it synced higher than 40Mb previously then this has probably been lost to crosstalk over the years.

If the DLM is reset by the ISP then the line will go right to 40Mb.
With stability it could go to just under 50Mb in time with a reduced SNRM target.

Ignore the CRC count.
The DLM is interested in the ES count.
This plays no part in the capping of the sync and the ES rate is low.

Edited by j0hn83 (Sun 27-Dec-20 13:57:53)


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Standard User MercuryRH2
(newbie) Sun 27-Dec-20 15:23:25
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Re: Flaky FTTC and frequent dropouts


[re: milesharrison] [link to this post]
 
My parents had a similar situation recently and after talking it through with their ISP (Zen) we identified a line fault. DLM had drooped the line steadily from a stable 40/10 to just 7/0.7. BT said there was nothing wrong but having insisted the line was the issue, Openreach duly came out and found ‘a cracked connection’ causing a high resistance issue. There was also noise on the line at times. The pair was repaired and everything went back to 40/9 with a stable 7ms latency and it’s been that way for several weeks.

I had to play on my parents being elderly and needing the line sorting out. Fortunately I found a sympathetic support body at BT who got it sorted.

They’ve had trouble with that line for years and the Openreach engineers have in the past said the overhead lines need replacing but no one at OR will sanction it because it’s too expensive.

Edited by MercuryRH2 (Sun 27-Dec-20 15:25:16)

Standard User 4M2
(knowledge is power) Sun 27-Dec-20 18:41:20
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Re: Flaky FTTC and frequent dropouts


[re: milesharrison] [link to this post]
 
In reply to a post by milesharrison:
Total time = 22 hours 59 min 18 sec
FEC: 11241 7
CRC: 575 5
ES: 11 5
SES: 11 0
UAS: 66 55
LOS: 1 0
LOF: 7 0


I would report an intermittent broadband fault and request a SFI engineer - something is causing ES, SES and a LOS.
Standard User j0hn83
(fountain of knowledge) Sun 27-Dec-20 19:48:46
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Re: Flaky FTTC and frequent dropouts


[re: 4M2] [link to this post]
 
In reply to a post by 4M2:
In reply to a post by milesharrison:
Total time = 22 hours 59 min 18 sec
FEC: 11241 7
CRC: 575 5
ES: 11 5
SES: 11 0
UAS: 66 55
LOS: 1 0
LOF: 7 0


I would report an intermittent broadband fault and request a SFI engineer - something is causing ES, SES and a LOS.


Every single time DLM resynced my line i received i burst of CRC and exactly 11 ES.

These occurred during the resync process.

There's not a single ES or CRC in 23 hours of sync time apart from those that happened during the resync.

Pointless reporting this. It's normal.

Edit: I'll add to that... Even if the 11 ES were not caused by a resync (they were) it would be ridiculous to report 11 ES in a 23 hour period to an ISP.

Edited by j0hn83 (Sun 27-Dec-20 19:51:46)

Standard User MercuryRH2
(learned) Sun 27-Dec-20 20:03:55
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Re: Flaky FTTC and frequent dropouts


[re: j0hn83] [link to this post]
 
In reply to a post by j0hn83:
Edit: I'll add to that... Even if the 11 ES were not caused by a resync (they were) it would be ridiculous to report 11 ES in a 23 hour period to an ISP.


I only have 9 on my l8ne and that’s running normally, so nothing to see here.
Standard User 4M2
(knowledge is power) Sun 27-Dec-20 21:42:00
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Re: Flaky FTTC and frequent dropouts


[re: j0hn83] [link to this post]
 
In reply to a post by j0hn83:
Every single time DLM resynced my line i received i burst of CRC and exactly 11 ES.

These occurred during the resync process.

There's not a single ES or CRC in 23 hours of sync time apart from those that happened during the resync.

Pointless reporting this. It's normal.

Edit: I'll add to that... Even if the 11 ES were not caused by a resync (they were) it would be ridiculous to report 11 ES in a 23 hour period to an ISP.


Latest 15 minutes time = 14 min 18 sec
FEC: 2275 0
CRC: 575 0
ES: 11 0
SES: 11 0
UAS: 38 27
LOS: 1 0
LOF: 7 0
LOM: 0 0


If ES, SES and a LOS happens intermittently causing relatively frequent resyncs, which may be the case, then that suggests a line fault.
Standard User MHC
(sensei) Sun 27-Dec-20 21:49:38
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Re: Flaky FTTC and frequent dropouts


[re: j0hn83] [link to this post]
 
Have to agree, nothing out of te ordinary there.

I work with some comms systems where 50ES per hour is quite "normal".


~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

M H C


taurus excreta cerebrum vincit
Standard User j0hn83
(fountain of knowledge) Sun 27-Dec-20 22:18:22
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Re: Flaky FTTC and frequent dropouts


[re: 4M2] [link to this post]
 
Broadcom modems show 10/11 ES (and often hundreds of CRC) on every single DLM initiated resync.
Every single 1.
It happens on many resyncs not caused by the DLM also.

The line has 0 ES outside that 15 minute minute window.
0 ES means 0 CRC.
So all of those 575 CRC were at the exact same time as the ES (1 CRC is a minimum 1 ES. 100 CRC can be 1ES).
The 11 SES are caused by the 11 ES.
The DLM initiated resync is the 1 LOS reported.

To the untrained eye the error figures are low enough
To the knowledgeable they are zero.

Excluding the DLM initiated resync there's not a single LOS, CRC or ES.

There's a low amount of FEC but even millions an hour of them is ok.

That's not to say there's no issues with the line.
It is currently banded.

The error figures are low though, and don't justify contacting an ISP on any line.
Knowing how the DLM causes ES on Broadcom modems i know there are zero CRC, ES, SES or LOS in those 23 hours of stats.

Edited by j0hn83 (Sun 27-Dec-20 22:20:54)

Standard User 4M2
(knowledge is power) Sun 27-Dec-20 23:52:24
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Re: Flaky FTTC and frequent dropouts


[re: j0hn83] [link to this post]
 
In reply to a post by j0hn83:
The 11 SES are caused by the 11 ES.


I was under the impression that SES (Severely Errored Seconds) are worse than an ES (Errored Second.) Only one event is needed to trigger an ES. A Severely Errored Second is a one second period which contains 30% or more errored blocks. Could therefore 11 SES, in a relative time period, result in a LOS and a subsequent resync? If that were to happen fairly regularly then that would surely indicate a probable line fault and an investigation by a SFI engineer.
Standard User j0hn83
(fountain of knowledge) Mon 28-Dec-20 00:39:28
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Re: Flaky FTTC and frequent dropouts


[re: 4M2] [link to this post]
 
In reply to a post by 4M2:
In reply to a post by j0hn83:
The 11 SES are caused by the 11 ES.


I was under the impression that SES (Severely Errored Seconds) are worse than an ES (Errored Second.) Only one event is needed to trigger an ES. A Severely Errored Second is a one second period which contains 30% or more errored blocks. Could therefore 11 SES, in a relative time period, result in a LOS and a subsequent resync? If that were to happen fairly regularly then that would surely indicate a probable line fault and an investigation by a SFI engineer.


They aren't actual errors.

They occur during the DLM resyncing the line.

Would you like that in another language?
Standard User milesharrison
(newbie) Mon 28-Dec-20 01:11:02
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Re: Flaky FTTC and frequent dropouts


[re: j0hn83] [link to this post]
 
In reply to a post by j0hn83:
That's not to say there's no issues with the line.
It is currently banded.

The error figures are low though, and don't justify contacting an ISP on any line.
Knowing how the DLM causes ES on Broadcom modems i know there are zero CRC, ES, SES or LOS in those 23 hours of stats.


I'll rephrase, the symptom is the internet stops working entirely during frequent periods over the day. The internal equipment is fine so it must be a line issue. I thought that posting the stats might help narrow down the problem rather than use them as a basis to report an issue.

The CRC errors DIRECTLY (within the preceeding 15min period) coinsided with the only occasion during the previous 24hrs that the line lost sync and retrained so seem to be a relavent symptom of the problem. There were ZERO recorded CRC errors before this happened and 575 during the event. Whether the total is low or high, whatever caused the line ro resync, it happened the same time as those CRC errors.

I didn't notice it as I wasn't using the internet, but it retrained about 45 mins ago (00:15) which is almost the exact time it retrained last night. Is that a BT function for weak lines or does it suggest some sort of local interference? Also noticed the upstream line rate has dropped by about 2mbit from that posted in my previous line stats.

Obviously I need to get plusnet to arrange a visit from BT, but just was curious to know if anything seemed distinctly out of the ordinary to help narrow down the problem before they send an engineer that will just plug in a machine that says it is working fine (during his test).
Standard User j0hn83
(fountain of knowledge) Mon 28-Dec-20 01:19:22
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Re: Flaky FTTC and frequent dropouts


[re: milesharrison] [link to this post]
 
In reply to a post by milesharrison:
The CRC errors DIRECTLY (within the preceeding 15min period) coinsided with the only occasion during the previous 24hrs that the line lost sync and retrained so seem to be a relavent symptom of the problem. There were ZERO recorded CRC errors before this happened and 575 during the event. Whether the total is low or high, whatever caused the line ro resync, it happened the same time as those CRC errors.


I knew that without you telling me that, which is why i was stressing the 11 ES/SES is of no concern.

It's likely the DLM making adjustments to your line.
For example it could be turning G.INP on or off on the upstream.


I didn't notice it as I wasn't using the internet, but it retrained about 45 mins ago (00:15) which is almost the exact time it retrained last night. Is that a BT function for weak lines or does it suggest some sort of local interference? Also noticed the upstream line rate has dropped by about 2mbit from that posted in my previous line stats.


Yes again it's the DLM making adjustments. It needs to resync the line to do this.
Sometimes it will do this every other day, sometimes once a month.
You may find upstream G.INP is now off (the upstream INP will have changed from 44) which is why the sync is a little lower.

There was likely another 10 or 11 downstream ES coinciding with this resync.
It's normal.

Could you post the new stats?

Edited by j0hn83 (Mon 28-Dec-20 01:20:27)

Standard User milesharrison
(newbie) Mon 28-Dec-20 01:58:55
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Re: Flaky FTTC and frequent dropouts


[re: milesharrison] [link to this post]
 
A once a day or every other day retraining they could live with, but not multiple periods throughout the day where the internet either slows to a complete crawl (<3mbps actual throughput) or stops entirely for 10 mins (without a retrain event) ruining whatever they are watching on netflix etc.

However I can't see why a daily retraining would be necessary under normal circumstances. My VDSL at home will sit happy for a month on end without a retrain. If we could limit hers to say 20mbit to improve stability, it would be a dissappointing, but effective improvement.

There has been water ingress in the wires which is almost certainly the problem with her connection. I'm just wondering what way we can get a permenant solution to improve its reliability. One BT engineer moved (extended) the master socket to another room to avoid a bad corner of damp. That didn't help. The next one moved it up the wall by a meter to table level to help get it away from the damp, but that didn't help.

The water is in the line and I imagine the damage is done. Surely the solution would be to replace the copper running from the telegraph pole. I am trying to find a way of convincing them that that's necessary as their solutions fail and probably cost them more in the long run with repeat visits. Had a look at the BT Wholesale checker to spy on her neighbours using their phone numbers. They're all synced between 45-55mbit.

Addition: Just conked out again, approx 1:45 after the last retrain. Upstream is back to where it was, but Downstream is quite a bit less. The speed however isn't really a concern. It's the stability.

====================================================================================
VDSL Training Status: Showtime
Mode: VDSL2 Annex B
VDSL Profile: Profile 17a
G.Vector: Disable
Traffic Type: PTM Mode
Link Uptime: 0 day: 0 hour: 0 minute
====================================================================================
VDSL Port Details Upstream Downstream
Line Rate: 8.501 Mbps 27.398 Mbps
Actual Net Data Rate: 8.502 Mbps 27.399 Mbps
Trellis Coding: ON ON
SNR Margin: 6.1 dB 12.6 dB
Actual Delay: 0 ms 0 ms
Transmit Power: 4.9 dBm 12.5 dBm
Receive Power: -8.7 dBm -14.8 dBm
Actual INP: 44.0 symbols 54.0 symbols
Total Attenuation: 0.0 dB 22.9 dB
Attainable Net Data Rate: 8.502 Mbps 40.966 Mbps
====================================================================================
VDSL Band Status U0 U1 U2 U3 U4 D1 D2 D3
Line Attenuation(dB): 9.2 40.2 59.1 N/A N/A 17.7 47.6 73.7
Signal Attenuation(dB): 9.2 39.6 57.8 N/A N/A 25.6 47.2 76.5
SNR Margin(dB): 6.1 6.1 6.1 N/A N/A 12.7 12.6 0.0
TX Power(dBm): 0.4 -2.5 1.3 N/A N/A 10.7 7.7 -128.0
====================================================================================

VDSL Counters

Downstream Upstream
Since Link time = 31 sec
FEC: 0 0
CRC: 0 0
ES: 0 0
SES: 0 0
UAS: 0 0
LOS: 0 0
LOF: 0 0
LOM: 0 0
Latest 15 minutes time = 11 min 55 sec
FEC: 1920 0
CRC: 535 0
ES: 10 0
SES: 10 0
UAS: 37 27
LOS: 1 0
LOF: 5 0
LOM: 0 0
Previous 15 minutes time = 15 min 0 sec
FEC: 11 0
CRC: 0 0
ES: 0 0
SES: 0 0
UAS: 0 0
LOS: 0 0
LOF: 0 0
LOM: 0 0
Latest 1 day time = 7 hours 41 min 55 sec
FEC: 2908 4
CRC: 535 1
ES: 10 1
SES: 10 0
UAS: 97 87
LOS: 1 0
LOF: 5 0
LOM: 0 0
Previous 1 day time = 0 sec
FEC: 0 0
CRC: 0 0
ES: 0 0
SES: 0 0
UAS: 0 0
LOS: 0 0
LOF: 0 0
LOM: 0 0
Total time = 7 hours 41 min 55 sec
FEC: 2908 4
CRC: 535 1
ES: 10 1
SES: 10 0
UAS: 97 87
LOS: 1 0
LOF: 5 0
LOM: 0 0

Edited by milesharrison (Mon 28-Dec-20 02:01:14)

Standard User j0hn83
(fountain of knowledge) Mon 28-Dec-20 10:00:00
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Re: Flaky FTTC and frequent dropouts


[re: milesharrison] [link to this post]
 
The Downstream has been further banded/capped by the DLM.
This time it is capped at 27.4Mb

Again, not a single CRC, ES or SES outside what is forced by the DLM when it lowered the banding.

There are ALWAYS 10 or 11 ES/SES when the DLM takes a line offline for a resync.

If the line wasn't capped it would sync around 41Mb.
Stable and with a reduced SNRM it would nudge 50Mb.

Banding isn't applied due to errors but due to multiple resyncs.

I've no idea what is causing the banding.

Do you keep rebooting the modem? Why does the total time counter keep resetting?
Rebooting the modem is seen as instability by the DLM.

Edited by j0hn83 (Mon 28-Dec-20 10:01:23)

Standard User MHC
(sensei) Mon 28-Dec-20 10:17:01
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Re: Flaky FTTC and frequent dropouts


[re: milesharrison] [link to this post]
 
In reply to a post by milesharrison:
I didn't notice it as I wasn't using the internet, but it retrained about 45 mins ago (00:15) which is almost the exact time it retrained last night. Is that a BT function for weak lines or does it suggest some sort of local interference? Also noticed the upstream line rate has dropped by about 2mbit from that posted in my previous line stats.


Keep a watch tonight and tomorrow ... if te same time, then there is a possibility of an external source. Heating/hot water circulating pump, street light, ...


~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

M H C


taurus excreta cerebrum vincit
Standard User Zarjaz
(eat-sleep-adslguide) Mon 28-Dec-20 14:04:11
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Re: Flaky FTTC and frequent dropouts


[re: milesharrison] [link to this post]
 
There has been water ingress in the wires which is almost certainly the problem with her connection. I'm just wondering what way we can get a permenant solution to improve its reliability. One BT engineer moved (extended) the master socket to another room to avoid a bad corner of damp. That didn't help. The next one moved it up the wall by a meter to table level to help get it away from the damp, but that didn't help.

Sounds to me like you ought to get the damp issue within the property sorted first of all.

Standard User 4M2
(knowledge is power) Mon 28-Dec-20 19:22:20
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Re: Flaky FTTC and frequent dropouts


[re: j0hn83] [link to this post]
 
In reply to a post by j0hn83:
Again, not a single CRC, ES or SES outside what is forced by the DLM when it lowered the banding.

There are ALWAYS 10 or 11 ES/SES when the DLM takes a line offline for a resync.


Thank you for correcting my misreading of the OP's stats. When I have seen in particular numerous SES and a LOS prior to a resync I have wrongly attributed those SES to a line fault leading to a LOS both of which are reported by the modem/router stats. A modem/router system log may simply just say the DSL link is down and when one looks at the detailed stats numerous SES and a LOS can be seen and thus an incorrect assumption can be made.

Cheers smile
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