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Author Topic: Wide Swings in SNR Margin for a VDSL2 Service with BT  (Read 279 times)

xlr8r

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Wide Swings in SNR Margin for a VDSL2 Service with BT
« on: June 14, 2021, 11:00:47 AM »

[Moderator note: This topic has been split off from the What's my expected SNR Margin for BT thread.]

spotted this topic and wanted to know if anyone can advise on a solution for a similar problem i have with BT VDSL.

I use a Zyxel router (in bridged mode) for modem. and an Asus GT-AX11000 router. Im on FTTC and Cabinet is a Huawei i believe having looked it up)

Every day my line will drop for no apparent reason on the Zyxel (also happens with BT Openreach modem)

Also, Each day my DOWN SNR sits stable (at 5.5) until around 8:30 am when it jumps up to 9.2 ?? it does this every day, and reduces again around 9pm to normal.  (see screenshot)

what could cause such a sudden SNR increase ? Ad what could be causing my dropouts ? (let me know if you need any additional data for diagnosis)

thanks


====================================================================================
    VDSL Training Status:   Showtime
                    Mode:   VDSL2 Annex B
            VDSL Profile:   Profile 17a
                G.Vector:   Enable
            Traffic Type:   PTM Mode
             Link Uptime:   0 day: 12 hours: 48 minutes
====================================================================================
       VDSL Port Details       Upstream         Downstream
               Line Rate:     11.368 Mbps       59.806 Mbps
    Actual Net Data Rate:     11.338 Mbps       59.807 Mbps
          Trellis Coding:         ON                ON
              SNR Margin:        6.2 dB            9.3 dB
            Actual Delay:          0 ms              0 ms
          Transmit Power:        6.6 dBm          13.8 dBm
           Receive Power:        0.0 dBm          -6.3 dBm
              Actual INP:        0.0 symbols      55.0 symbols
       Total Attenuation:        0.0 dB          20.7 dB
Attainable Net Data Rate:     11.338 Mbps       70.380 Mbps
====================================================================================
  VDSL Band Status        U0      U1      U2      U3      U4      D1      D2      D3
  Line Attenuation(dB):     N/A    29.9    48.6     N/A     N/A    15.3    38.4    62.2   
Signal Attenuation(dB):     N/A    29.0    47.3     N/A     N/A    18.0    38.0    62.4   
        SNR Margin(dB):     N/A    6.2    6.2     N/A     N/A    9.4    9.3    9.3   
         TX Power(dBm):     N/A   -13.0    6.6     N/A     N/A    11.6    7.9    5.3   
====================================================================================

            VDSL Counters

           Downstream        Upstream
Since Link time = 48 min 51 sec
FEC:      47929003      68
CRC:      65      4
ES:      1      4
SES:      1      0
UAS:      0      0
LOS:      0      0
LOF:      0      0
LOM:      0      0
Latest 15 minutes time = 14 min 51 sec
FEC:      229043      1
CRC:      0      0
ES:      0      0
SES:      0      0
UAS:      0      0
LOS:      0      0
LOF:      0      0
LOM:      0      0
Previous 15 minutes time = 15 min 0 sec
FEC:      265174      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 = 14 hours 29 min 51 sec
FEC:      53381868      79
CRC:      3126      8
ES:      48      8
SES:      48      0
UAS:      1740      1693
LOS:      1      0
LOF:      3      0
LOM:      34      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 = 14 hours 29 min 51 sec
FEC:      53381868      79
CRC:      3126      8
ES:      48      8
SES:      48      0
UAS:      1740      1693
LOS:      1      0
LOF:      3      0
LOM:      34      0
====================================================================================

   
« Last Edit: June 15, 2021, 04:19:47 PM by burakkucat »
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tubaman

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Re: Wide Swings in SNR Margin for a VDSL2 Service with BT
« Reply #1 on: June 14, 2021, 11:33:03 AM »

...

Every day my line will drop for no apparent reason on the Zyxel (also happens with BT Openreach modem)

Also, Each day my DOWN SNR sits stable (at 5.5) until around 8:30 am when it jumps up to 9.2 ?? it does this every day, and reduces again around 9pm to normal.  (see screenshot)

what could cause such a sudden SNR increase ? Ad what could be causing my dropouts ? (let me know if you need any additional data for diagnosis)

...
 

This sounds like some kind of electrical interference occurring only overnight - a faulty streetlight perhaps? Does the line drop coincide with the change of SNRM as your stats are puzzling, showing the circuit being unavailable for nearly 30 minutes (based on UAS count) in 14.5 hours of uptime. Is it really offline for that long or did you take it down manually?
 :)
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xlr8r

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Re: Wide Swings in SNR Margin for a VDSL2 Service with BT
« Reply #2 on: June 14, 2021, 11:50:16 AM »

This sounds like some kind of electrical interference occurring only overnight - a faulty streetlight perhaps? Does the line drop coincide with the change of SNRM as your stats are puzzling, showing the circuit being unavailable for nearly 30 minutes (based on UAS count) in 14.5 hours of uptime. Is it really offline for that long or did you take it down manually?
 :)

hi thanks.

This has been happening for years now. I had thought of the streetlight as being a possible culprit but the times are nowhere close. the SNR drops to normal overnight and jumps up again around 8:30am-ish daily.

ill run dsl stats for a couple of days to get a better graph to indicate full days times affected.

i have had the line unplugged a couple of time over last few days (to swap modems for testing)  but i gave it 30 mins each time, so as not to get DLM'd.

will post back when i have a better graph ... thanks
« Last Edit: June 14, 2021, 12:41:31 PM by xlr8r »
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xlr8r

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Re: Wide Swings in SNR Margin for a VDSL2 Service with BT
« Reply #3 on: June 15, 2021, 10:24:34 AM »

ok, so here is a days worth of SNR roller-coaster'ing....

anything here make any sense to anyone ?

i have tried to determine if anything in my house goes on and off that similar times, but can find nothing... Im stumped with this SNR behaviour....

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tubaman

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Re: Wide Swings in SNR Margin for a VDSL2 Service with BT
« Reply #4 on: June 15, 2021, 10:47:49 AM »

Sudden large changes like that are almost certainly due to electrical interference. The offending device may not be in your house of course, but the only way to prove it isn't is to switch off everything bar your modem/router to see if it changes. A drop from 9.3 to 2.4 is pretty severe so something must be happening then.
 :)
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BT FTTC 80/20 Huawei Cab - Zyxel VMG8924-B10A

xlr8r

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Re: Wide Swings in SNR Margin for a VDSL2 Service with BT
« Reply #5 on: June 15, 2021, 12:31:11 PM »

Sudden large changes like that are almost certainly due to electrical interference. The offending device may not be in your house of course, but the only way to prove it isn't is to switch off everything bar your modem/router to see if it changes. A drop from 9.3 to 2.4 is pretty severe so something must be happening then.
 :)

thanks, okay so if i can determine the problem isn't at my property, i can get onto BT and complain ?

also, what kind of device could generate such SNR changes on my line ?
« Last Edit: June 15, 2021, 12:36:55 PM by xlr8r »
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meritez

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Re: Wide Swings in SNR Margin for a VDSL2 Service with BT
« Reply #6 on: June 15, 2021, 02:29:36 PM »

thanks, okay so if i can determine the problem isn't at my property, i can get onto BT and complain ?

also, what kind of device could generate such SNR changes on my line ?

An old tv set, for example: https://www.bbc.co.uk/news/uk-wales-54239180
Do any of your neighbours experience issues?
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xlr8r

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Re: Wide Swings in SNR Margin for a VDSL2 Service with BT
« Reply #7 on: June 15, 2021, 03:37:28 PM »

An old tv set, for example: https://www.bbc.co.uk/news/uk-wales-54239180
Do any of your neighbours experience issues?

nope, nothing internal in my property goes on or off at the times indicated on the graph .... most bizarre !
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Alex Atkin UK

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Re: Wide Swings in SNR Margin for a VDSL2 Service with BT
« Reply #8 on: June 15, 2021, 04:00:34 PM »

nope, nothing internal in my property goes on or off at the times indicated on the graph .... most bizarre !

Unfortunately as seen in the article, it doesn't have to be in your property and can be VERY hard to narrow down if it isn't.
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