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A BT guy climbed my pole, and I lost 9Mbps

LordFox
Rising Star
Posts: 224
Thanks: 13
Registered: ‎10-03-2008

A BT guy climbed my pole, and I lost 9Mbps

As soon as I got FTTC, I had a rock solid 80Mbps connection. My Modem (VMG8924) even told me 90Mbps was attainable. I'm within spitting distance of the cabinet and can see the exchange from my living room window.

Then one morning, a year or so ago, I saw a BT guy climbing the pole that my line (and other houses' lines) comes from. My connection dropped for a few hours (nice of him to warn us... not!) and when it came back, I had 71Mbps. Damn him!

I've been stuck on that ever since. Which of the following numbers are responsible for that? I'm not that hot on DSL details, but I'm guessing its the SNR margin. Unfortunately I don't recall what the stats were previous to the drop because it had been so stable for so long that I stopped looking. Yes, I've just reset my modem (hence the 1 minute uptime)

====================================================================================
    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: 1 minute
====================================================================================
       VDSL Port Details       Upstream         Downstream
               Line Rate:     20.063 Mbps       71.153 Mbps
    Actual Net Data Rate:     19.999 Mbps       71.154 Mbps
          Trellis Coding:         ON                ON
              SNR Margin:        7.2 dB            6.4 dB
            Actual Delay:          0 ms              0 ms
          Transmit Power:        6.7 dBm          13.0 dBm
           Receive Power:       -9.7 dBm          -1.3 dBm
              Actual INP:        0.0 symbols      48.0 symbols
       Total Attenuation:        0.0 dB          14.9 dB
Attainable Net Data Rate:     21.770 Mbps       71.809 Mbps
====================================================================================
  VDSL Band Status        U0      U1      U2      U3      U4      D1      D2      D3
  Line Attenuation(dB):	 4.6	 19.4	 30.2	  N/A	  N/A	 9.8	 23.2	 37.2	
Signal Attenuation(dB):	 4.6	 18.6	 29.2	  N/A	  N/A	 11.0	 22.9	 37.2	
        SNR Margin(dB):	 7.3	 7.2	 7.2	  N/A	  N/A	 6.4	 6.4	 6.4	
         TX Power(dBm):	-5.4	-23.8	 6.5	  N/A	  N/A	 9.5	 7.8	 7.0	
====================================================================================

 

22 REPLIES 22
Gandalf
Plusnet Help Team
Plusnet Help Team
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Registered: ‎21-04-2017

Re: A BT guy climbed my pole, and I lost 9Mbps

Our testing isn't showing any issues or anything we can raise to Openreach for investigation and as you're within the speed estimates of your line, I doubt if we booked an engineer visit they'll be able investigate further.

Fingers crossed with time you'll be back on a 80mbps sync.

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 Anoush Mortazavi
 Plusnet Help Team
LordFox
Rising Star
Posts: 224
Thanks: 13
Registered: ‎10-03-2008

Re: A BT guy climbed my pole, and I lost 9Mbps

Thanks for your reply. I know it's within the estimate so no one will do anything, that's why I've never bothered asking before (that, and things have taken my mind off the issue until recently).

It's not going to change now; it's been stuck like this for a year and the modem has been restarted enough times.

When I posted, I was thinking I could do things like tweak the SNR margin from this end. Then I discovered that's not possible with FTTC.

I wish I had thrown rocks at him and knocked him off the pole!!!

Gandalf
Plusnet Help Team
Plusnet Help Team
Posts: 19,304
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Registered: ‎21-04-2017

Re: A BT guy climbed my pole, and I lost 9Mbps

Ah fair enough. Personally my line's sub-50mbps (long way from the cabinet!) so I'm a tad jealous Smiley

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 Anoush Mortazavi
 Plusnet Help Team
dws1900
Aspiring Pro
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Registered: ‎17-09-2018

Re: A BT guy climbed my pole, and I lost 9Mbps

When I posted, I was thinking I could do things like tweak the SNR margin from this end. Then I discovered that's not possible with FTTC.

 

Yes it is, if you have a suitable modem.

I use it too eek out an extra 1mbs on my pathetic sub Superfast 24Mbs service.

You need to lookup why FTTC is a feeble system, its really just the laws of physics.

Google attenuation, radio crosstalk.

 

I wish I had thrown rocks at him and knocked him off the pole!!!

Why?, he/she did not invent this useless system.

 

 

 

 

LordFox
Rising Star
Posts: 224
Thanks: 13
Registered: ‎10-03-2008

Re: A BT guy climbed my pole, and I lost 9Mbps

@dws1900 which modem do you use?

I definitely read that the SNR margin could not be adjusted on FTTC/VDSL in an article on tweaking it on ADSL. I can't for the life of me find that article again though. I've not found out if my VMG8924 can do it yet. It looks like there are SNR-related settings in the xdslctl command but I'm a bit wary of just trying random things until I find out exactly what they do.

dws1900
Aspiring Pro
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Registered: ‎17-09-2018

Re: A BT guy climbed my pole, and I lost 9Mbps

I have a Vigor modem, and you can adjust the S/N, which I have done on occasions on my FTTC line.

Typically my S/N is 3-4 db, I have forced it to 2dB with a slight increase in speed, but typically more errors, so more resends and lower through put.

VDSL/ADSL technologies are very susceptible to interference, electrical noise, and line issues (bad joints, water ingress, cross talk). As it is using a radio signal this is to be expected. 

FTTP does not suffer as much, shame it did not get adopted twenty years ago.

 

 

Enverex
Hooked
Posts: 6
Registered: ‎13-12-2019

Re: A BT guy climbed my pole, and I lost 9Mbps

Those SNR tweak options only apply to ADSL by the way, they don't do anything on VDSL connections.

dws1900
Aspiring Pro
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Registered: ‎17-09-2018

Re: A BT guy climbed my pole, and I lost 9Mbps

Usage:
vdsl snr [delta]
  delta: SNR margin delta. The SNR margin delta should range from -50 to 50.
  delta=1 means 0.1dB.
  Current VDSL SNR Margin is 4 dB.
  Current VDSL SNR Margin delta setting is 0.
 
 
There is a corresponding option for adsl, so why would Draytek provide both?
I have used it in the past and the data back from the modem confirms the changes.
dws1900
Aspiring Pro
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Registered: ‎17-09-2018

Re: A BT guy climbed my pole, and I lost 9Mbps

re Those SNR tweak options only apply to ADSL by the way, they don't do anything on VDSL connections.

 

Please supply evidence of this claim. 

Enverex
Hooked
Posts: 6
Registered: ‎13-12-2019

Re: A BT guy climbed my pole, and I lost 9Mbps

Openreach themselves. It's handled entirely by the DSLAM for VDSL connections.

LordFox
Rising Star
Posts: 224
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Registered: ‎10-03-2008

Re: A BT guy climbed my pole, and I lost 9Mbps

That is what I read; that the DSLAM can't be overridden.

I've just come back here to say that I've tried with my Zyxel, which seems to have the correct commands, but it made absolutely no difference. I'm uncertain whether the Zyxel is trying to change VDSL settings, or only changing ADSL settings despite using the xdslctl commands. I did notice that changing the SNR margin only changed the resulting config output in the "ADSL-training" parameter, not where I expected. Changing the Max speed parameters instead of directly changing the SNRM had similar zero effect.

I give up. Whatever that BT guy did a year ago, it cost me 9Mbps. I'm tempted to prove my statement of "within spitting distance of the cabinet" from the bottom of my drive!

At least I found a firmware to enable baby jumbo frames, and got an extra eight bytes of MTU on my HE IPv6 tunnel. Yay 🙄 that'll really make up for the lost 9Mbps.

dws1900
Aspiring Pro
Posts: 404
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Registered: ‎17-09-2018

Re: A BT guy climbed my pole, and I lost 9Mbps

Openreach themselves. It's handled entirely by the DSLAM for VDSL connections.

 

That is not evidence, it is a statement, which needs backing up with verified documentation.

Enverex
Hooked
Posts: 6
Registered: ‎13-12-2019

Re: A BT guy climbed my pole, and I lost 9Mbps

Good luck getting Openreach's official technical documentation then.

Gandalf
Plusnet Help Team
Plusnet Help Team
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Registered: ‎21-04-2017

Re: A BT guy climbed my pole, and I lost 9Mbps

If it helps I can confirm that the DLM settings (SNR etc) for FTTC are handled by Openreach at the cabinet. 

Unlike ADSL where DLM’s at the exchange and we have a fair bit of control, neither ourselves nor BT Wholesale can change the SNR of FTTC lines.

I’ve never tried as I don’t have a capable modem to change the SNR settings but I’d be surprised if you could do this yourself on an FTTC line.

Having said that, if someone’s tried it and it’s worked then I can’t argue with that Lips_are_sealed 

If this post resolved your issue please click the 'This fixed my problem' button
 Anoush Mortazavi
 Plusnet Help Team