FEC errors can be caused by many different things, line faults, RF interference, rein, crosstalk and of course the profile your service provider or in the case of BT, DLM decides to assign. One of the things not mentioned in this forum yet is cross talk, cross talk is the transfer of unwanted signal energy from one circuit to another, adsl and other digital circuits give off a lot more cross talk (or transferred signal energy) than analogue services such as POTS (plain old telephony service). Now that more and more people are signing up for adsl then the crosstalk in Openreach cables is increasing like you wouldn't believe, this is not deemed as a fault! . I have seen circuits synching at 12meg eventually run down to 7.5meg, what was the fault? there was no fault! just that the available signal received at the router was being partially swamped by somebody else's adsl signal. Basically if you are the only digital circuit in a 20 pair cable feeding a block of flats then HOORAH you should be ok, but when the other 19 flats get converted to adsl then you WILL be affected, your SNR will drop and FEC errors will increase as your router tries to determine between the signals it receives!
don't worry when FTTP(fibre to the premises) arrives there will be no more attenuation, no more rein, no more noise and no more crosstalk!
