Thanks for posting that. This gives a clearer image. This is
almost as I predicted. Perhaps U1 was not allocated at sync but bitswapped into it after?
The QLN shows that U1 is a bit noisy (which is, of course, due to interference), hence why the SNR is a bit lower and not smooth here, and it would explain why a lot of bitswapping is occurring to maintain a minimum SNR margin of 6 dB on the tones in that band. Everything else checks out as being normal (though someone here will point out if there is something else of importance).
Let me ask the following:
- What modem are you using?
- What filter are you using?
- Are you currently plugged into the master socket or a slave socket?
Reference to question 3, if you are using a slave socket then I would suggest using the master socket (main socket, first point of entry for the copper pair). You can use
https://kitz.co.uk/adsl/socket.htm and
https://kitz.co.uk/adsl/btsockets.htm as guides to finding your master socket. I would also highly suggest that you plug the filter directly into the test socket (as pictured clearly in the first provided link) as this eliminates any internal socket wiring issues. Once you have done that, post QLN, bitloading and SNRM per band.
Are you getting any significant errors? I don't know how long you have been running DSLstats for, but the MTBE (Mean Time Between Errors; higher is better) I can see is approx. 260 on the downstream and 520 on the upstream. So the DLM certainly isn't going to be making any negative changes based on what we know.
I cannot comment on whether this constitutes a fault with the line necessarily since, while U1 looks to be impacted and subject to interference, the sync speed is not impacted and has a decent margin overall in the bands. I have confidence that you're always going to receive 20 Mbps upstream. You could request a line test from the ISP, but most "big" ISPs will have support (1st line) that will question "why?" since you have no visible deterioration to sync speed or errors. But you could still give it a go (though there is probably no need) after you've gone ahead and done what has been suggested by people on the forum.
Edited to correct "lower" to "higher".