DSL (or VDSL, Very High Bitrate Digital Subscriber Line) typically works by dividing the frequencies used in a single phone line into two primary "bands". The ISP data is carried over the high-frequency band (25 kHz and above) while the voice is carried over the lower-frequency band (4 kHz and below). The user typically installs a DSL filter on each phone. This removes the high frequencies from the phone line, so that the phone only sends or receives the lower frequencies (the human voice). The DSL modem and the normal telephone equipment can be used on the line at the same time without interference from each other.