I lost my internet a few days ago so I promptly called the phone company. They did their normal tests, while on the phone with me, to only discover what I already knew, they had to send a technician out. Since this has happened several times before the tech and I know each other well. Before it has been issues at the switching station, bad modem or the cable between the modem and the wall jack. So I checked all of those that I could from here before he showed up. The tech checked the switching station before coming here. We quickly found out the issue was in the wiring in the house. After two days of trying to find and fix the problem with out having to pull new wires, if you have ever had to pull a wire through a finished wall you will know why this is to be avoided if possible. The conclusion we came to is mice had partially chewed through the phone lines and two were shorting across each other. The partial short was what took so long to figure out what the issue was. The phone would still work but the DSL would not.
Here is where my tip comes in. When we remodeled and added onto the house back in 1991 I was doing heating and air work at the time so I knew the wire used for phones and thermostats is the same size. Generally phones lines are just two wires. Thermostat wire can go from two wires up to eight wires. I had a spool of four wire thermostat wire I used for phone wire because I wanted to have the option of adding in a second phone line for my office. Turns out that saved some headaches with this current problem. I had the tech check and see if the two wires I had left over for the second phone line, that never got used, were any good. Sure enough those two were still good so we hooked those up inside the house and in the box outside the house and were back in business. My tip is to use four or eight wire for phone lines even if you only need two. It may save you having to rewire your house in the future.