Moreover, sometimes tones 410-415 are used, sometimes not, sometimes tone 478 is used, sometimes not.
Thank you very much for your time
konrado5
But this is by design. What you describe is exactly how ADSL is supposed to work. If there is noise on the line, some tones (where the noise is located) aren't going to be used, or if they are, the bitloading will be vastly reduced. Whilst the 'notch' in your graph is obvious, nobody here can offer an explanation as to
why it is there. We simply don't know.
In any case, even if you resolved that notch, I doubt that you would see much improvement in speed.
As I see it, you have 3 options from here. You can either :-
1) Accept your line for what it is, complete with 'notch', and agree your speed isn't that bad.
2) Assume your ISP has, for some unknown reason, fitted a filter, and change ISP.
3) Keep asking what/why/how/if questions that nobody here (and I know of no other forum with more highly qualified experts than this one) can answer.
I hesitate to say it, but you seem to have a 'bee in your bonnet' regarding the condition of your line. I can sympathize with you but as far as I can see, there is
nothing you can do about it. You need to accept this, and move on.
With no ill will intended,
BE