I have telephone service from AT&T, and DSL from Earthlink.
A while back my DSL went totally dead. The modem indicated that there was no connection to the DSL modem at the other end. Eventually Earthlink had an AT&T man come by, who spent a lot of time checking the wiring in my house and eventually found that the trouble was somewhere out there in the telephone plant, believe he said pair gain equipment. He said there are cards in there that go bad sometimes, and he switched my line to a different pair and that fixed it all up.
Now I'm having a different problem - the DSL modem indicates that it has a solid connection to the DSL modem at the other end, but the Internet connection keeps going away and coming back. There's supposed to be an AT&T man coming to look at it again.
It would help if I understood how all this works. DSL modem on copper pair at my house goes somewhere out in the city to some apparatus but not direct to the telephone office. I don't know where the DSL modem at the far end is, nor whether it is owned by AT&T or by Earthlink, nor how the DSL modem out there connects to the Internet.