I dont think I have anything else to say other than whats already been said.
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>>> it is implicited by lowering line quality because of time ( I don't know how to translate it. I think about: line quality is worse if the more time elapsed).
This is usually the effect of what we call crosstalk.... ie the more people that join the cab, then speeds get lower. There isnt anything you can do about that.. Im sure Ive mentioned several times, that when I was 1st on a brand new shiny adsl2+ MSAN I could easily get 24/2.7 Mbps. A few years later it was something like 21Mbps.
If you read the VDSL sections you also see lots of us talking about it. Those of us first on new DSLAMs are finding several months later that we are losing a heck of a lot of speed. BE has lost circa 20Mb, I lost nearly 20Mb in about 9 months. BT is well aware of it, unfortunately the faster speeds mean we lose more
Its why we are waiting for a new technology called vectoring to come in as this lessens the effects of crosstalk.