Broad Bandwidth

A standard telephone installation consists of a pair of copper wires that the phone company installs in your home. The copper wires have lots of room for carrying more than your phone conversations- they are capable of handling a much greater bandwidth or range of frequencies, than that demanded for voice. DSL exploits this "extra capacity" to carry information on the wire without disturbing the line's ability to carry conversations. The entire plan is based on matching particular frequencies to specific tasks.

Earlier using Plain Old Telephone Service, limits the frequencies that the switches, telephones and other equipment will carry. Human voice, speaking in normal conversational tones, can be carried in a frequency range of 0 to 3400 Hertz (cycle per second). This range of frequencies is tiny comparing this to the range of most stereo speakers, which cover from roughly 20 Hertz to 20,000 Hertz. And the wires themselves have the potential to handle frequencies up to several million Hertz in most cases. By limit the frequencies carried over the lines, the telephone system can pack lots of wires into a very small space without worrying about interference between lines. Modern equipment that sends digital rather than analog data can safely use much more of the telephone line's capacity. DSL does just that.

Most homes and small business users are connected to an asymmetric DSL (ADSL) line. ADSL divides up the available frequencies in a line on the assumption that most Internet user look at, or download, much more information than they send or upload. Under this assumption, if the connection speed from the Internet to the user is three to four times faster than the connection from the user bac to Internet, then the user will see the most benefit (most of the time).