Dropping when phone rings

[#1]

After a couple of months of great stability (uptimes of 3 to 4 weeks), my connection has once again returned to dropping when an incoming call is made. It doesn't appear to drop at any other time, and it doesn't drop every time there is an incoming call.
Before the long stretch of stability, I did some experimentation with different routers and filters (ringing from my mobile), and all showed the problem to some extent. The sync rate didn't make any difference either - even if the initial sync rate was considerably lower than average, it would drop.
It would drop even if there was no phone connected to the line - is the issue with the line card in the exchange perhaps?
My current router is a BT Business Hub (2wire 2700HGV) and it can log the noise margin at the point that the connection is lost. In every instance of a dropped connection, the noise margin is still high (typically >6dB and sometimes approaching 7dB).
I'm a bit concerned about raising a fault. I am currently on a fixed 6dB profile, since DLM kept bumping up the noise margin. The thing is, even once DLM hit the highest noise margin, the connection was still dropping. This mirrors my experiments when I adjusted the noise margin with my other router (which I am not currently using).
<rant>Of course, the only people who ring the house phone are telemarketers, which makes the issue all the more annoying!</rant>

[#2]

On the DSL Diagnostic page what is the exit code given when the connection is dropped?

[#3]

Mostly ERR_LOS_LIMIT. On a couple of occasions it has been ERR_LOF_LIMIT.

[#4]

Faults like this are one of around 2 or 3 things normally. Both of these have happened to me so...
1) Filter, Dont use a cheap crappy thing included with a router. Personally id get one of these if im using ADSL... ADSL Nation
2) Low voltage on the phoneline (usually caused by a bad junction or water on the line - had this twice before BT OR could clear it for me...) (in which case you'd need to raise a fault, BUT make sure you've adequately checked internal wiring AND filters (not cheap!) AND routers to ensure it IS an external problem, getting BT to even look at this problem was difficult for me )
Regards

[#5]

I am currently using an ADSLNation filter. Also tried a couple of different Excelsus models and Speedtouch-branded one.

[#6]

The last time that the OpenReach engineer came out, he mentioned that there was an issue with the power on the line, something to do with it decreasing as soon as sync was made if my memory is correct. He suggested that the problem was more local to the exchange than the cabinet/house.
If this is as good as it gets, I'm willing to accept that. After all, I'm getting 2Mb on a long line with between 67dB and 73dB attenuation (depending on what range of frequencies it is measured across). I don't want to do anything to make it any slower though - I would rather have a resync or two a day than put up with 1Mb, for example. My concern is that the line was equally as unstable when it was being banded with a 1152kbps cap.

[#7]

Any more ideas?

[#8]

Quote from: CX23882

It would drop even if there was no phone connected to the line - is the issue with the line card in the exchange perhaps?

It may be your master socket - what type of master socket do you have and do you have any extension wiring?

[#9]

It's a new OpenReach-branded master socket (with the bell wire filter).
Extension wire is literally a single 2.5m run of cable up to one socket. The drops occur even when connected to the test socket though.

[#10]

Hi CX23882,
If that's happening in the test socket with two different filters then it's probably an issue with filtering in the exchange, which needs to be raised as a broadband fault - if you do so at http://faults.plus.net (raise it as a dropping connection issue) we'll get it raised and sorted for you.

[#11]

I will raise a fault if the disconnections resume, but at the moment, it's appears stable again (typical!  :))