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devera
Aspiring Expert
1,107 Views
Message 1 of 67

What causes SN margin to drop when landline is called?

I've been with BT Infinity 2 since July 2013 and at first I used to get around 58 Mbps. Over the years this has dropped to 49 Mbps. Last October 2015 I noticed a sudden drop from 49 Mbps to 39 Mbps which I complained about but nothing was really done about it so just left it. I noticed from the line stats graphs there is increased noise.

 

Last Monday things have become worse. I noticed the SN margin fluctuating between 0 to 6 db and attainable rates from 30 Mbps to 18 Mbps then back up to around 38 Mbps. I could also near some static noises on the phone line, a recording is here: https://www.sendspace.com/file/22u6fb

 

I also noticed the following occurs:

 

The SN margin drops when:
-Landline is called (without any telephones connected)
-Landine is called (with telephones connected)
-Landline is picked up

 

This sudden SN margin drop causes errors which nearly drops the connection.

 

Below are some graphs from 30 September 2015 and today 9 March 2016

 

Bits_with_SNR-20150930-1754-HIGH_RES.pngBits_with_SNR-20160309-1004-HIGH_RES.pngQLN-20150930-1754.pngQLN-20160309-1004.png

 

So now I've managed to schedule an engineer home visit, I'm just concerned I may be charged £130 but I'm certain there is nothing wrong at my end.

 

Does this look like a problem between the cabinet and the master socket?

 

Kind regards

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66 REPLIES 66
Webby
Distinguished Sage
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Message 2 of 67

Re: What causes SN margin to drop when landline is called?

If you have noise on the line when connected to the test socket, unless the telephone is the cause of the noise, you won't be charged. The charge is something that HAS to be mentioned in the event that the customer has said they've done the relevant internal checks but actually haven't. The noisy line will most likely be the route cause of all of the issues you've mentioned (fluctuating SNR, drop in sync etc)
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devera
Aspiring Expert
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Message 3 of 67

Re: What causes SN margin to drop when landline is called?

Hi, yes, there is still static noise (you have to really listen carefully) even when connected to the test socket and also with another telephone.

 

Did you hear the recording I uploaded?

 

Do you think the engineer would be interested in seeing these graphs too to further support my case?

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Webby
Distinguished Sage
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Message 4 of 67

Re: What causes SN margin to drop when landline is called?

I never listened to the recording no. Have you raised it as a telephone line fault or a broadband fault? If the former, the engineer probably won't be interested as he may not be DSL trained. Even if it is a broadband trained engineer, they will have their own test equipment that they will use to help identify any issues.
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devera
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Message 5 of 67

Re: What causes SN margin to drop when landline is called?

I think it was raised as a telephone fault.
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devera
Aspiring Expert
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Message 6 of 67

Re: What causes SN margin to drop when landline is called?

Engineer came and could not fix the fault at my end. He said the line card at the exchange might need replacing.

 

Why does the SN margin still drop when the phone is picked up? Sometimes it's enough to cause the FTTC connection to drop.

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Webby
Distinguished Sage
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Message 7 of 67

Re: What causes SN margin to drop when landline is called?

Not sure why he didn't go and change the line card, quite strange. The noise margin drops because there's an increase in noise(not always audible) on your line. If it is too high, beyond the target margin, then the line will have too many errors causing a drop in connection.

I suspect another engineer visit is required, perhaps broadband trained.
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devera
Aspiring Expert
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Message 8 of 67

Re: What causes SN margin to drop when landline is called?

He said he goes by protocol and doesn't do more than the job required or he'll get scolded as previously.

 

I showed him some graph stats from my HG612 modem but again he said he can't do any more than test the line in that visit.

 

The line tested OK from the test socket but I still don't know why when the phone line is in use the SN margin drops disrupting the broadband connection.

 

It's as if the sudden burst of electricity when making a call causes interference with the VDSL2 signal.

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Webby
Distinguished Sage
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Message 9 of 67

Re: What causes SN margin to drop when landline is called?

As I've explained, something (unknown) is causing excess noise when the phone is in use. There could be a dodgy phone, dodgy filter, high resistance fault, a fault at the cabinet, or a fault at the exchange.

When this "noise" happens, it is interfering and causing problems with the frequencies that your broadband connection uses, interupting the packets of data causing errors. Too many errors in a short period of time will ultimately stop data transmission and cause the connection to drop.

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john46
Distinguished Sage
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Message 10 of 67

Re: What causes SN margin to drop when landline is called?

could be a high resistance joint which certainly needs an engineer visit
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