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15db Noise Margin after years working at 9db.

Community Veteran
Posts: 3,366
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Registered: 06-04-2007

15db Noise Margin after years working at 9db.

After many years happily working at 9dB, the BT line monitor at the exchange is now putting our line onto a 15dB setting, which reduces my speed from 2.5Mb to 1.5Mb.
I had started adding to the thread over here but thought I would put a thread here as it is more on topic and may be found more easily if other people come looking if they find they have a similar issue.
At the end of April there was a genuine line fault, before this date the line was running at 9dB reliably.
The line fault was fixed, a few days later I saw the SNR had gone up tp 12, and asked PN to get BT reset the SNR back to 9dB, this happened on May/2nd.
A few weeks later, June/29th, the SNR goes up to 12db, then to 15dB on July/5th.
A few days ago, PN got BT to put the SNR back to 9dB. Just a few days later, and with no re-sync events, it has gone back to 15dB.
Now running the RouterStats, and it tells me very a very many FEC/CRC errors even when there is no data going across the line. The BT line monitor is seeing all these line errors and increasing the SNR to reduce them, which is good in theory, of course now my line runs a whole lot slower though.  Angry
This sugests there is a lot of noise on the line, possibly due to the repair back in April now becoming bad again, there is now a faint but noticeable click on the phone line (it occurs at little over 1s intervals, I counted 4 clicks in 5s ) when I the phone handset is off-hook.
I have tried with 3 different phones connected to the master socket, I can hear this click with all of them.
The router has been plugged into the master socket using a different micro-filter, this makes no difference to the FEC/CRC errors, they just keep increasing.  Lips are sealed
I am looking to PN for thoughts about should this be raised a voice fault or an ADSL fault?
Thoughts appreciated from any party.
SW.

typo, fix link to show where other discussion had started on this problem
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56 REPLIES
Superuser
Superuser
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Registered: 06-04-2007

Re: 15db Noise Margin after years working at 9db.

Do you still hear the clicks if you disconnect your router from the line? (Unplug the modem cable, plug the phone into the test socket (via a filter) to isolate any effects from internal wiring.)
If clicks are still present then reporting a voice fault to your phone service provider seems appropriate, as long as there isn't an open broadband fault on your line.
Hopefully if Openreach fix that, the behaviour on the broadband side should return to normal, and when that is proved PN will be able to get your target noise margin reduced again.
David
Community Veteran
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Re: 15db Noise Margin after years working at 9db.

Quote from: spraxyt
Do you still hear the clicks if you disconnect your router from the line? (Unplug the modem cable, plug the phone into the test socket (via a filter) to isolate any effects from internal wiring.)

Yep, have done that too and still hear the clicking, which I did not say so explicitly above.
Indeed I am thinking about getting it raised a voice fault, but wanted to get folks here to check what I have done and suggest other things I could try before getting PN/BT to spend time on this ... I do not like to be a timewaster.  Undecided
SW.
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Grafter
Posts: 60
Registered: 30-07-2007

Re: 15db Noise Margin after years working at 9db.

SW
It looks as if there is a line fault and you are picking up induced ground currents.  Try dialling 17070 and then option 2 for a quiet line test.  This will give you a terminated phone line which should be quiet.  If is not quiet then go straight to the operator on #150, don't waste time with the automated test.  Telephone lines should be balanced without any refernce to earth since that way they get minimum pickup but with all the joints and differing environments in the cabinets etc, it is not always possible to achieve perfect balance.
As a matter of interest, do you live in a rural retreat, as it could be an electric fence which relies on a ground return?  just a thought.
Cheers
Bob
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Re: 15db Noise Margin after years working at 9db.

Yes, I do live out in the sticks and am in the proximity of electric fences, but there always been and did go have look to see if the grass is reaching any of the electrified wires and could not see any, the sheep do a good job of keeping the grass trimmed.
SW.
silly typos fixed.
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Grafter
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Registered: 30-07-2007

Re: 15db Noise Margin after years working at 9db.

Hi SW
as you say the problem is only recent which means that somewhere along the telephone line there is a fault on the cable that is effectively conducting one side to earth.  This is where all this "electronic rubbish" is and  giving you this problem. 
If, the line back to the exchange is properly balanced (ie equal current in both wires of the telephone line) then there would be minimal pickup since there theorectically would be no transfer of the earth currents along your line in an attempt to find a way to earth.
BT use a device called a "Time Domain Relectometer"  or their name is a "Hawk" and it will immediately see all the transitions and faults along the line.  It has a distance measuring capability to actually pinpoint where the problem is.  It sends a pulse along the line and a pulse gets reflected where the imperfections are.  It is a marvelous piece of kit. 
They even use the same technique for use on fibre and you can see every join for miles - but I digress :-)
If it were fibre you would not have any problem with conducting eath currents,
cheers
Bob
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Registered: 31-08-2007

Re: 15db Noise Margin after years working at 9db.

Undoubtedly go for raising a voice fault and keep moaning until your line is quiet.
If you're a BT line rental customer dial 151 and select the option to speak to an adviser. Don't bother with the auto test and don't mention BB. Once that's sorted, BB improvements can follow.
Regards.
Community Veteran
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Re: 15db Noise Margin after years working at 9db.

I have ticket 25861975 open on this one, left a long reply to the ticket last night ... no update yet today. Sad
SW.
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Community Veteran
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Re: 15db Noise Margin after years working at 9db.

Ticket 25861975 seems to be stuck in a hole, can somebody kick it and the person who last left a reply. The last person to reply from CSC was no doubt well meaning, the fact it had been +24 hours waiting for a reply from PN looks bad on the statistics, I hope that was not thier motivation. Sad
SW.
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VileReynard
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Re: 15db Noise Margin after years working at 9db.

I've always found that speed issues are progressed on the basis that the fault doesn't lie with BT.
If you have any knowledge/experience of broadband then this is discounted.
You need to progress to Stage II Smiley - after making absolutely sure that the fault is not at your end!
I'd like to see a response which is tailored to the technical level of the customer.

James
Grafter
Posts: 21,036
Registered: 04-04-2007

Re: 15db Noise Margin after years working at 9db.

Hi SW,
I've read your ticket and have seen your references to a broadband engineer.
However, your request on the ticket was to have your noise margin changed to 9dB.  As of the last test, this was showing as being at 10dB, which suggests that you don't have a target noise margin of 15dB.
Are you still seeing fluctuations in noise?
Community Veteran
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Registered: 06-04-2007

Re: 15db Noise Margin after years working at 9db.


The whoosh test, or whatever it is called this week indeed only shows you what the current SNR margin is, at the moment it maybe 10 or 12db. When the router connects the initial SNR value is 15db.
See this copied from the ticket:
Quote
<<<>>><<<>>><<<>>><<<>>><<<>>><<<>>>
1. Do you lose your connection only at certain times of the day, or is it all the time? If only at certain times, please say when.
There is no pattern

<<<>>><<<>>><<<>>><<<>>><<<>>><<<>>>
2. How long has the problem been happening and when did it start?
It happened after t/storms and a line fault which BT fixed a few months ago. See ticket numbers 24891693 (getting the line fault fixed) and 24902396 (getting the SNR target put back to 9dB).

<<<>>><<<>>><<<>>><<<>>><<<>>><<<>>>
3. What are you doing at the time of the fault (e.g. downloading large files). Does your connection drop when idle?
The connection is not dropping, PN had BT put the SNR target margin back to 9dB (this value had been stable for many months before the line faults occured mentioned above). At 9dB, there are now many FEC and CRC errors, that BT see and decide to increase the SNR target to 12dB and then 15dB over a few days after it being set to 9dB.
<<<>>><<<>>><<<>>><<<>>><<<>>><<<>>>
4. When you lose your connection is sync lost on the modem/router (i.e. does the ADSL link light start flashing or does it remain solid green?)
Not Applicable, BT are raising the SNR margin without the line loosing sync.
<<<>>><<<>>><<<>>><<<>>><<<>>><<<>>>
5. Do you have any other equipment on the telephone line which may affect the service (e.g a fax machine) . Is your PSTN (voice) service working OK?
There is a faint but audible click on the phone line, it repeats at about 1s intervals. It is because of this symptom I opened this ticket, the BT Field Engineer has been here and reccomends a Broadband Engineer is sent to investigate.
<<<>>><<<>>><<<>>><<<>>><<<>>><<<>>>
6. Please connect your modem/router to the master telephone socket, leaving all other equipment disconnected. See if the problem still happens.
Yes, done this. When the target SNR was still 9dB, I connected the modem to the test socket, I still got the high number of FEC/CRC errors reported by the modem.
<<<>>><<<>>><<<>>><<<>>><<<>>><<<>>>
7. Has another modem/router been tested on your telephone line, or have you tested your modem/router on another telephone line which you know works OK?
No.
<<<>>><<<>>><<<>>><<<>>><<<>>><<<>>>
8. Have you changed the micro filter to see if this is a problem?
Yes.
<<<>>><<<>>><<<>>><<<>>><<<>>><<<>>>
9. Are you on a particular website when you lose your connection?
No.
<<<>>><<<>>><<<>>><<<>>><<<>>><<<>>>
10. Is the session actually disconnecting (e.g. so you have to login again), or is it reducing to almost nothing (e.g. the session stays connected, but it is hardly usable)?
Kind of. Because the noise repeats at about 1s intervals, I guess if I click on a URL at the same time there is the impulse of noise, that the message does not leave the modem and the web browser just sits 'waiting fo reply from ...'.
<<<>>><<<>>><<<>>><<<>>><<<>>><<<>>>
11. Can you reconnect again straight away, or do you have to reboot?
Not applicable. I am not loosing sync.
<<<>>><<<>>><<<>>><<<>>><<<>>><<<>>>
12. Do you use any other protocols and applications other than your web browser, email and FTP?
Yes.
<<<>>><<<>>><<<>>><<<>>><<<>>><<<>>>
13. Do you get an error code when you log on again?
No, this is not a logging in problem.
<<<>>><<<>>><<<>>><<<>>><<<>>><<<>>>
14. Have you added microfilters to all used points?
I have a filtered faceplate and do not need to do this.
<<<>>><<<>>><<<>>><<<>>><<<>>><<<>>>
15. Is there an alarm system on the property which uses the telephone line?
No.
<<<>>><<<>>><<<>>><<<>>><<<>>><<<>>>
16. Have you anything else connected to your PC besides the modem/router?
No.
<<<>>><<<>>><<<>>><<<>>><<<>>><<<>>>
17. Please make sure that your modem/router stays switched on and plugged into the telephone socket. This will allow us to check your problem and make further tests.
The modem is never turned off.


Oh Yes, there are fluctuations in noise. Sad
SW.
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Community Veteran
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Re: 15db Noise Margin after years working at 9db.

Another poor reply, again quoting the results of the whoosh test. Sad
I added the following to see if this helps to make progress.
Quote
Maybe I can describe this a different way with an analogy.
I have a car, which I have owned for many years and could drive it at 70MPH on the motorway, one day it breaks down and take it to the garage for repair. The garage fix the car, but now when I take it onto a motorway it can only get to 50MPH.
If this happened would you be thinking the repair was not carried out correctly by the garage and be asking questions?
So, to put this in terms of my broadband connection, for a long time the line had a 9dB SNR value (which allows the line to run at 2.5Mb), after a fault which BT fixed the line has a 15dB SNR value (which makes the line run at about 1.7Mb). So after the repair by BT, the line nows performs poorly.
Is this now clear?
SW.


What amazes me is that all I am asking for is PN to carry out the request of the BT Field Engineer which is for them to get a Broadband Engineer to visit my house!  Shocked
SW.
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VileReynard
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Re: 15db Noise Margin after years working at 9db.

I think BT might say that phone lines only have to be capable of carrying voice signals.
So to follow your analogy, your car is still moving...  Crazy

Community Veteran
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Re: 15db Noise Margin after years working at 9db.

Yep. aware of that.
Just had another CSC guy run a whoosh test, then replaied saying they can ask BT to lower the target margin to 9dB and they warn me, it could go back up again ... Yep it will now since this line fault.
SW.
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