Yesterday evening I had a more-or-less stable (up for 3 hours at least), albeit slow (2400 d/s) connection. Line attenuation was reported as 21db, and noise margin was also about 21db (downstream). Overnight the connection looks to have got very unstable again - with multiple drop-outs since about 3am. I notice that line attenuation has jumped up to 49/24 (down/up) and noise margin is back in single figures (9db), connection speed is down to 2200 / 324(!).
I understood line attenuation to be related to the distance to the exchange, if so why can it more than double?