>> BT say they have increased the bRAS profile to 6000Kbps
Like roseway, I cant understand why you may have been told that they reset the bRAS to 6000kbps. The bras profile follows, and is entirely dependent at the rate that you sync to the exchange at. - not the other way round. It is lower than your sync speed as an allowance is made for IP overheads (hence the other name its often known as - IP profile).
Theres a list of IP profiles in relation to sync speed at the bottom of this page
http://www.kitz.co.uk/adsl/IPprofile.htm which may help you understand how it works.
>> Speed 4544 Kbps; Attn 45db; SNR varies between 11 & 14db (it used to be 6.0 when all was well and Attn has always been 45dB)
That actually seems about right - and on the good side at that - for a 45db atten line with a 12dB target SNR.
Attenuation shouldnt change thats related to the physical length and condition of your line. SNR fluctuates depending upon local conditions and interference. Its normal to see fluctuations during the course of the day, usually lower in the evenings when more people are at home.
However
target SNR is a configurable attribute of the DLM system. If at one point you have had a problem with your line, then the DLM will have increased this from the default 6dB in 3dB stages to try and stabilise your line.
>> have found a fault
Reading through the lines it is possible perhaps that there was at one point there was something that triggered the fault in the first place an oxydised joint is a common cause (rust on one of the many connectors between the exchange and your home to you and me), but it could have been a few things.
>> done any testing or increased the bRAS has the router shown any disconnections or loss of sync.
This well could have occurred over the xmas period.. for the target SNR to have been altered , the problem is more likely to have started a period of time before hand.
Christmas tree lights are actually a well known cause of adsl problems. Possibly the combination of this and a slight rusty joint could have tipped your line just sufficient over the edge for the DLM to start playing with your target SNR. I dont think anyone will ever be able to say for sure though.
>> SNR varies between 11 & 14db
If you are now monitoring with routerstats and your SNR _never_ goes below the 11db then it would seem that whatever work was carried out has actually sorted your line fault.
Unfortunately though you may well be stuck with the target SNR figure for a while, since target SNR is one of those things that may correct itself in a few weeks or months.
To attain the highest sync speed you can then you are best perhaps trying a resync when your SNR Margin is at its highest.
If I were you I would continue to monitor your SNR Margin and if it never goes much outside those figures, then I would approach my ISP and request that they asked BTw to reset the Target SNR back to the default of 6dB. This will have the effect of enabling you to sync back at more like your previous higher speeds.
If you are going to attempt this route.. be forewarned... BT (ISP) helpdesk firstline support are probably not going to understand what you are on about - they arent always trained to understand the actual theoretics of how adsl works. Therefore you are best being armed with as much info as you can first.
If you haven't already done so, read
An explanation of SNR and SNR Margin to help press your point. I would go along the line of "obviously it would appear I had a fault that has now been fixed/stabilised.. but its my target SNR that is now keeping my sync speed low.. can you please request BT Wholesale to reset it".
Some ISPs are more successful than others at being able to get BTw to do this.
Obviously I cant say for sure... but since you say you first noticed the changes in Dec.. I wouldnt be too surprised if something like flashing xmas tree lights had a part to play in it.. and its why now your SNR Margin is now stable within normal parameters.. but unfortunately the "damage has now been done" and youre seeing the effects of a higher target SNR. Theres a reason why the DLM needs to do this.. and a fairly large amount of lines do need a higher Target SNR to remain stable.
Unfortunately the DLM isnt able to differentiate if its one of those "seasonal things" - or if it is a line that really does need a higher Target SNR to remain stable.
Hope this all makes sense.
Good luck and please let us know how it goes.