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FTTC S/N level changes

RGN01
Dabbler
Posts: 11
Registered: ‎14-07-2018

FTTC S/N level changes

Is it normal for the S/N ration to vary significantly in a short space of time? 

I have been struggling with very variable speeds on my FTTC circuit for some time now but today noticed the Signal to Noise ratio varying significantly and quickly, accompanied by sync speed changes. This only seems to affect the 'down' speed, not the 'up' speed and the up S/N ratio stays pretty much stable at 6 to 6.1

 

Typical situation is (readings taken randomly over the past 10 - 15 minutes):

                  S/N              Max Rate (Kbps)

1                5.1                20982

2                5.3                 21152

3                3.3                17756

4                4.2                20615

5                4.8                20804

Downstream attenuation is 22.9 and that seems stable.

I have tried new microfilters and have connected to the test socket directly. There are no extensions and the supply cable comes through the wall into the wall box so there is no other internal wiring. I've even cabled directly from the test socket to the router (removing the phone and filter) and all these seem to give very similar results.

 

I've tried various modems / routers and all give the same variations in speed although not all provide the S/N ratio and sync speed so those above were recorded with a TP-Link TD-W9970

 

Any help or suggestions gratefully accepted - I've just started a new job and can't be here when an engineer can be so I must try to sort this myself.

Thanks.

Richard

22 REPLIES
Baldrick1
Aspiring Hero
Posts: 2,009
Thanks: 848
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Registered: ‎30-06-2016

Re: FTTC S/N level changes

If this happens on a wired connection then your wifi can be eliminated.

There are two factors at play, signal and noise. The question is, which is causing the variation? Is it a fault developing in the transmitted signal that's reducing the signal or is it increased noise level? Either will be identified as reduced SNR. Are there any other stats available from your router that could resolve this question?

The reduced speed perhaps indicates that it's interference that's knocking out some of the broadband frwuencies.

It would help if your modem is capable of running a program such as dslstats, where you could see the effect on the frequency spectrum. Do you have this option?

RGN01
Dabbler
Posts: 11
Registered: ‎14-07-2018

Re: FTTC S/N level changes

Thanks for your response, Baldrick1.

 

Sorry, should have said that this is all on wired network. The WD-9970 only provides the following so I don't think I'll get much more from it unfortunately:

  Upstream Downstream
Current Rate (Kbps) 5222 20437
Max Rate (Kbps) 5315 20766
SNR Margin (dB) 6 4.9
Line Attenuation (dB) 55.2 22.9
Errors (Pkts) 0 0

 

I wasn't familiar with dslstats so have downloaded it and am experimenting. Thanks.

 

Richard

 

Baldrick1
Aspiring Hero
Posts: 2,009
Thanks: 848
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Registered: ‎30-06-2016

Re: FTTC S/N level changes

I fear that according to this you will not get it to run with your router http://dslstats.me.uk/routers.html

RGN01
Dabbler
Posts: 11
Registered: ‎14-07-2018

Re: FTTC S/N level changes

That seems to be the case but I have managed to get a telnet session up on it - but can't figure out anything useful to do with it! It isn't accepting any commands I've tried (ls and xdslctl are two that I've tried, the latter a suggestion from a Google search).

 

I'll try a bit more, I really need to sort this.

 

I have a BT HH5 and a HH6 that I could try but don't know if these will work with the PlusNet line and whether they can be monitored.

Richard

Community Veteran
Posts: 5,228
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Registered: ‎10-06-2010

Re: FTTC S/N level changes

Is the connection dropping and re-connecting, or is it only the SNRM and max rate changing? The max attainable rate reported by the modem doesn't affect your actual download speed. If it's only the SNRM and max rate varying, it's not really much of a problem.

Baldrick1
Aspiring Hero
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Thanks: 848
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Registered: ‎30-06-2016

Re: FTTC S/N level changes

Both these routers will work with Plusnet, the Plusnet Hub One is a HH5a with tweeked firmware. Unfortunately neither will work with DSLstats. 

RGN01
Dabbler
Posts: 11
Registered: ‎14-07-2018

Re: FTTC S/N level changes

Te connection is not resetting - well not at present anyway. It has been unstable over the past few weeks but seems Ok at the moment.

 

The download speed is varying a lot - this is what got me started investigating - to the point that sometimes Youview / BT Sport won't work over it. I couldn't find a reason for it and ended up looking at the router stats and that is when I realised that there seems to be a correlation between this S/N ratio changing and download speed.

 

RGN01
Dabbler
Posts: 11
Registered: ‎14-07-2018

Re: FTTC S/N level changes

Thanks, I may try them and try to find a suitable monitoring tool. Right now the existing one seems OK and I'm too nervous to change anything in case it comes back slower so I'll try those later.

 

Just to close out the telnet on the W9970 part of this discussion, I managed to get it working but could not find a way to get stats - all it seems to offer is viewing settings and changing config.

 

Thanks again for your help!

 

Richard

Baldrick1
Aspiring Hero
Posts: 2,009
Thanks: 848
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Registered: ‎30-06-2016

Re: FTTC S/N level changes

Try doing a quiet line test when the speed is down. Ring 17070 then select option 2. If there's noise on the line then report a phone fault

RGN01
Dabbler
Posts: 11
Registered: ‎14-07-2018

Re: FTTC S/N level changes

Thank you. Will do! Thumbs Up

turbotippy
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Registered: ‎03-04-2018

Re: FTTC S/N level changes

SNR margin varies constantly. It can be influenced by almost everything from the number of users on the cabinet, nearby electricity cables, even the weather. Here's my stats for the last 14 days.

dsl4.png

RGN01
Dabbler
Posts: 11
Registered: ‎14-07-2018

Re: FTTC S/N level changes

Thank you, turbotippy. I understand that but was under the impression that anything below about 6db was not good, so my 3.3. had me worried but yours seems to hover around 5.5 for long periods - what speed are you getting?

 

Also, what are the guidelines? Where should I be getting concerned?

 

Richard

turbotippy
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Posts: 22
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Registered: ‎03-04-2018

Re: FTTC S/N level changes

Here the speed is irrelevant really, I live pretty much next door to the cabinet and get 80Mbps. I was hovering around 6dB and around 75Mbps for weeks, then DLM obviously made a change and it dropped the SNRM and resynced me to 80Mbps a few days ago.

6dB SNRM may give a more stable line than a 3dB SNRM. DLM will decide which level it should be at over time based on the numbers of errors it sees. i.e. if your line shows that it is very stable at 6dB SNRM then DLM may reduce the SNRM over time which will increase speed, but potentially also increase errors.

Where to get concerned, well my concerns would be if I was around 6dB and getting frequent disconnects or high error rates.

RGN01
Dabbler
Posts: 11
Registered: ‎14-07-2018

Re: FTTC S/N level changes

Thank you. I wish I could get speeds like that - I find the current speed limiting for what I need to do - but I have no alternatives so need to eke out every bit of performance I can get!

I'll keep an eye on it all!

Richard