raichu wrote
Why don't they allow the DSLAM to sync dynamically at the best possible speed?
It does, but the upper limit is the connection speed set by your ISP. I have seen many people with an extremely noisy 256Kbps connection sync at 96 or even 64Kbps. And sometimes they just get "Your DSL connection is down".
I am surprised you can still even sync at 256Kbps down with those stats. The SN/ Margin drop from 22 to 11dB is also alarming.
Usually, S/R Margin does drop a bit at night or when the weather is wet (winter rainy day)... and you get some HEC/CRC/FEC errors when there is nearby thunder. But it shouldn't drop that much.
As I said you have a lot of errors (most critical are HEC and CRC). FEC are corrected errors where the packet did not need to be resent.
Your "down" line attenuation (which increases the further you are from the Central office) is also bad but not the worst I have seen.
I have seen people with 69 or 70dB (the max value some "Speedtouch" modems will display, so it could theoretically be higher) run perfectly on a 256Kbps connection.
The only thing you can do from your side is, as I mentioned before, change the cable connecting your modem to the phone box for the building/chalet where you are in case there's a loose connection somewhere or it's an old one. Get something like "CAT5e" which should be shielded against electromagnetic interference.
Your ISP can try to change your ADSL modulation to another type as mentioned by Ahmad Toutounji.