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Contributor
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Message 1 of 17

0.3 Noise Margin on Downstream

Hello,

 

I'm experiencing quite a few disconnections per day (6 or more) on my BT Infinity connection.  I tried BT support (online chat) and they did a 'reset', but that doesn't appear to have resolved the issue.

 

 

Here are the current line stats, which look a bit odd to me.

 

Is a noise margin of 0.3 on the downstream within normal bounds?

 

5. DSL uptime:0 days, 14:23:36
6. Data rate:2274 / 21989
7. Maximum data rate:2101 / 16446
8. Noise margin:4.5 / 0.3

 

PS. These are the disconnection messages in the BT router log:

 

(116585.040000) PPPoE is down after X minutes uptime [Waiting for Underlying Connection (WAN Ethernet 2 -​ Down)]

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Distinguished Sage
Distinguished Sage
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Message 2 of 17

Re: 0.3 Noise Margin on Downstream

That is rather low, which does not surprise me as you are connected above. the max data rate for your line, which means that DLM is not doing its job properly.

 

Can you please disconnect the broadband input to the home hub, wait about 20 seconds, and then reconnect it, to see if it reconnects at a rate nearer to the max data rate, and with a higher downstream margin.

 

 

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Message 3 of 17

Re: 0.3 Noise Margin on Downstream

Hi Keith, thank you for your help.

 

I have disconnected the router form the line for 20 seconds. 

 

Current line stats are as follows:

 

6. Data rate:2172 / 27972
7. Maximum data rate:2065 / 25335
8. Noise margin:4.9 / 3.0

 

 

 

 

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Distinguished Sage
Distinguished Sage
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Message 4 of 17

Re: 0.3 Noise Margin on Downstream

That is better, 3dB is the correct value. Not sure were 0.3dB came from originally, unless it was simply a display error.

 

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Message 5 of 17

Re: 0.3 Noise Margin on Downstream

Thank you Keith!

 

Here are the current stats:

 

5. DSL uptime:0 days, 00:03:17
6. Data rate:2000 / 27796
7. Maximum data rate:2006 / 27613
8. Noise margin:5.9 / 3.3

  

I get a number of disconnections each day, which seems to have got worse over time.  This appears to coincide with the line running at higher speed, it used to be stable at around 21Mbps.  According to the logs, PPPoE goes down each time, then it reconnects about a minute later.

 

Would such an issue be classified as a fault and if not, is there a way to increase stability on the line? Please let me know if you need any further information, log extracts etc.

 

I did try the helpdesk, but didn't get very far (they don't seem to be well equipped to handle intermitent issues like this).

 

Many thanks,

Richard.

 

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Message 6 of 17

Re: 0.3 Noise Margin on Downstream

@richard42

Your line may not be capable of operating at the new lower margin. It may increase by itself, but I think it would be better for one of the moderators to ask for your target SNR to be reset back to 6dB, as the change to 3dB target is affecting your line stability. The connection rate is higher than the maximum available rate, so its going to disconnect.

 

Its funny, we seem to be going in a circle, as the lower margin was trialled before, a few years ago, with the same problems. Must be new management who have not looked at what happened last time Smiley Sad

Any speed gained is marginal, at the expense of stability.

 

I have asked a moderator to provide assistance, they will post an invite on this thread.
They are the only BT employees on this forum, and are based in the UK.

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Moderator-Retired
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Message 7 of 17

Re: 0.3 Noise Margin on Downstream

@richard42 I am sorry that you are having problems with your connection. 

 

Send over your details using the contact link within my profile and one of the team will be in touch to help.

 

Thanks,

OlgaC 

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Message 8 of 17

Re: 0.3 Noise Margin on Downstream

Hi Keith, Olga,

 

Thank you very much for your help.  I do seem to recall that the noise margin on the BT router status page used to be much higher (around 6) and the line was more stable back then.

 

Your suggestion sounds like a good way forward!

 

I have submitted my contact details via Olga's profile, referencing this thread.

 

Cheers,

Richard.

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Message 9 of 17

Re: 0.3 Noise Margin on Downstream

It was in 2012, when it was last trialled. Doesn`t time fly by Smiley Wink

 

See https://community.bt.com/t5/ADSL-Copper-Broadband-Speed/What-is-this-I-hear-about-BT-Trialing-3-0dB-...

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Message 10 of 17

Re: 0.3 Noise Margin on Downstream

Interesting link, thank you!

 

Here are the current stats:

 

5. DSL uptime:0 days, 09:03:09
6. Data rate:2121 / 28011
7. Maximum data rate:2134 / 24247
8. Noise margin:5.7 / 2.3

 

The noise margin doesn't appear to have been altered yet, I assume that's because of the Easter break.


Downstream is very low.  I'll report back once I hear from BT.

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