ADSL (Asymmetric Digital Subscriber Line) is a high-speed Internet access service that utilizes existing copper telephones lines to send and receive data at speeds that far exceed conventional dial-up modems.

The fastest dial-up modems are rated at 57 kilobits per second (Kbps), and usually operate at about 53 Kbps under good conditions. By comparison, ADSL allows datastream speeds from 1.5 to 8 megabits per second (Mbps), depending on the grade of ADSL service purchased.

ADSL uses standard telephone lines to transmit upstream and downstream data on a digital frequency, which sets these datastreams apart from the analog signals telephones and fax machines use. Because the ADSL signal is operating on a different frequency, the telephone can be used normally, even when surfing the Web with ADSL service. The only requirement will probably be inexpensive DSL filters on each phone or fax line, to remove any "white noise" on the line that might be generated from ADSL service.

The "asymmetric" in ADSL refers to the fact that the downstream data rate, or the data coming to your computer from the Internet, is traveling faster than upstream data, or the data traveling from your computer to the Internet. Upstream data rates are slower because Web page requests are fairly miniscule data strings that do not require much bandwidth to handle efficiently.

Some businesses, however, may require matching upstream rates for uploading large files. SDSL, or Symmetric Digital Subscriber Line is an option. "Symmetric" indicates that both datastreams are operating at the same speed of 1.5 to 7 Mbps, depending on the grade purchased. SDSL service requires a dedicated telephone line because, unlike ADSL, telephone and fax services cannot share a line with SDSL service.

ADSL is an "always on" service, meaning that as long as your computer is powered on, it will automatically stay connected to the Internet unless you manually disconnect via software or hardware. ADSL is especially suited for gamers, streaming multimedia and downloading large files.

ADSL is not available to everyone. DSL providers, or even your local phone company, can tell you if service is available in your locale. Speeds will vary depending upon your physical distance from local hubs.

A basic configuration of ADSL is the net card, software for the ADSL connection, the ADSL modem, a filter or splitter that separates voice of data and it lines of copper until the central phone.

Another basic configuration can be net card, router, the ADSL modem, splitter and it phone lines phone.

The router has its own software (firmware) to establish the ADSL connection.

The contracted speed corresponds to the speed maximum possible measure from the ADSL modem until the node of data connected.

The protocol also demands another exchange of data and they are transparent to the user but that however they consume broadband.

These data are those that maintain the connection between the client and the remote server, this is the reason because you can never reach a discharge to the contracted speed.

In the following table you can be seen each contracted nominal speed and the final result when carrying out a download.

For a reference, the percentage of lost varies between a 10% and 20% which depends on several factors, among them the connection type, the distance of the user until the phone central, the state of you line them of copper, the subscriber's possible interferences internal/external along the whole copper lines, etc.

kbps (kilobits per second) = KB/s x 8
KB/s (kilobytes per second) = kbps / 8