A DSL line filter will filter out the unwanted noise and connection problems that DSL internet service causes on a telephone. The filter consists of a plug which plugs into the wall outlet and 2 jacks. These jacks are clearly marked telephone and DSL for proper connection. ADSL splitter is just a regular phone splitter with a filter on one of the outputs. This allow the internet to work on your PC through the telephone line (connected to the modem of course). For an existing home involves installing DSL filters on every telephone, fax machine, voice band modem, and other voiceband device in the home, leaving the DSL modem as the only unfiltered device. For wall mounted phones, the filter is in the form of a plate hung on the standard wall mount, on which the phone hangs in turn.