Long Line Problem

[#1]

I have a long line to the exchange, (58dB attenuation), which is capable of sustaining a 3Mbps sync with a 9dB SNR for weeks on end.  Then something happens, noise or someone doing something at the exchange, and within a few hours I find myself with a 2Mbps sync and 15dB SNR.  Then I ask Plusnet for a SNR reset and all is well for another few weeks until it all happens again.
Last time BT acknowleged a fault, audible noise on the phone, and sent an engineer who tested my line thoroughly and said my line now tested fine.  He believed a corroded fuse at the exchange had been replaced.  SNR reset and all is well again for several weeks until 2 days ago when its all happened again!
I am getting tired of having to request SNR resets but I suspect that the length and age of my line mean that is the only way to get an acceptable speed.  Is there any way I can fix my SNR or reset it myself?  I am sure Plusnet have better things to do than keep resetting it for me.
Before anyone asks, yes I have done all the usual tests at the master socket and the drop line from the pole to my property was replaced last year.

[#2]

The target noise margin should go down on it's own eventually.
A single re-sync due to an isolated random burst of noise wouldn't cause the target SNR margin to be bumped up, so you should probably try to fix the cause of the problem instead of the symptoms. But I think your options for controlling the DLM depend on if you are on ADSL2 21CN or not.

[#3]

Hi HughA,
I wouldn't mind resetting the SNR but is there now way you can leave it in the test socket? Although the increases in the SNR may be external they could also be internal. Using the test socket would prove that one way or the other.
Jojo

[#4]

Quote from: ejs

The target noise margin should go down on it's own eventually.

30 days on 20CN is typical

[#5]

@HughA
Do you have any fixed extension sockets & wiring? If so what colour wires are connected to which terminal numbers on the faceplate you've taken off to get to the test socket?  Are you using any extension leads of any description?
Does your Master Socket look like the NTE5 or the ADSL faceplate?

[#6]

Thanks for all the input folks.  Because of its location its not practical to leave the router plugged in to the test socket permanently and it would need to stay there for at least a month or two to prove anything.
Master socket is fitted with a filtered baseplate and ring wire has been disconnected there and at both extension sockets.  Router is connected to a dedicated pair run from the unfiltered connections on the faceplate. 
The last event a few days ago had 4 resyncs in about a 12 hour period which caused the SNR to rise from 9 to 15 in 2 stages.  RouterStats is showing a steady 15dB SNR now and it will probably stay like that for some time now until Jojo orders a reset for me (please).
Perhaps what I've got is as good as its going to get and I'll have to settle for 2Mbps until I can get fibre.
HughA

[#7]

That all sounds quite good as far as the filtered plate etc goes and your phone sockets. The only information missing is the detail about the dedicated pair, which is why I asked about the colour or the wires as this tends to indicate what the cable may be. If however you know what the standard of the cable was, stating that would do, ie was it CW1308 or perhaps Cat5e or another standard of twisted pair.

[#8]

Not sure of the extension cable type but it has the usual 2 twisted pairs.  I'm using the orange/white white/orange pair to connect to the router.
I'm pretty sure the problems are outside the property, when the line is bad using the test socket doesn't improve things.
Line is still good this morning, no resyncs for 36 hours.

[#9]

OK, that sounds fine. When you said a few weeks in your OP. how long is a few weeks roughly? Is it a consistent interval, in other words can you reasonably predict when it might next happen?

[#10]

Quote from: Anotherone

Quote from: ejs The target noise margin should go down on it's own eventually. 30 days on 20CN is typical

I timed my own line getting back from 15dB to its normal 6dB after a line fault.  It took approximately 400 hours per 3dB step.

[#11]

Well you must have been lucky then, perhaps your 20CN exchange is a bit more modern, but that's not the experience of the majority of those on 20CN exchanges.

[#12]

Is there a convenient power supply by the master socket? If so could you leave the router there and use homeplugs to get ethernet where it is needed?

[#13]

In reality I don't think the internal setup is making a blind bit of difference.

[#14]

A line reset would be appreciated Jojo if you have a minute.  The line has been stable for 4 days now.
Many thanks
HughA

[#15]

Hi there,
In all probability we'll be in exactly the same set of circumstances in a few weeks when things drop again which does make me reluctant to do the line reset - I realise it's awkward leaving the router in the test socket but unless things have changed then I don't think there's any point in doing another line reset. I realise it'd get you an extra 1Mb on the speed for the few weeks it'd last but ideally we need the line to retrain at its best possible speed which it will only do in the test socket I'm afraid.