Digital Subscriber Line (DSL) provides high-speed digital modem technology via a conventional telephone line.

DSL uses signal frequencies above those used by voice or fax, so the DSL signal does not interfere with telephone conversations or faxes. When a DSL filter is connected to your phone jack, its function is to split the data (Internet) traffic from voice (phone) traffic, and route them separately.

Voice traffic (talking on the phone and fax signals) goes to the phone or the fax machine, while your data traffic (surfing the Web, downloading large files or photos) goes through the DSL modem and then to your computer, thus allowing you to use both at the same time.

The diagram below illustrates the key elements of DSL.