This (windows) tool reads out line data and error states from the famous SpeedModems 50B(+) and 200 (which are in fact CellPipe 19A-BX-AR modems with various
firmwares). The software might work on other modems with Trendchip chipsets, I don't know. Please try it.
DSL as in ADSL or SDSL is very sensitive to line quality since most telephone lines are unshielded and therefore quite vulnerable to radio interference. Also, very long
lines either outside or inside your house can affect the signal big time. I experienced a lot of these problems here (which caused the modem to sync at a rate way too
slow and irregular disconnections from the internet). There were other tools which displayed SNR (signal noise ratio) over frequency and line attenuation on other
modems. The model I had, however, wasn't supported. So one day I came up with this handy tool.
Troubleshooting
In most cases the tool cannot access the modem behind routers. On devices running Linux, like WRT54G(S) using a
DD-WRT firmware these three command lines might help you though: