The following graphs provide some evidence of the bebox/dslam not optimising a capped line or some other bug.
Bebox (TG585v7 latest firmware) on a capped 12Mb line, attenuation 34dB
First graph: 6dB SNRM, sync 12Mb, power 19dBm
http://i44.tinypic.com/1ietmf.jpg
Second graph: 9dB SNRM, sync 12Mb, power 19dBm
http://i44.tinypic.com/15ezeq9.jpg
Increasing noise margin to 9dB reduces bits across all tones, however sync remains unchanged at 12Mbit, and therefore the line isn't optimised at 6dB . I believe this is what some people are seeing.
Edited by deleted (Sun 27-Nov-11 20:43:14)