Asymmetric Digital Subscriber Line (ADSL)

An asymmetric digital subscriber line (ADSL) is a modem technology that enables information and video to be transmitted over regular telephone lines.

Though the mechanics of Internet access is highly technical, intuitively, the concept of ADSL is relatively simple: the use of regular copper wire phone lines to transmit data as well as voice.

For years, this idea of sending information over phone lines meant customers had to use what can now be called "old-fashioned" Internet providers -- those that provided "dial-up" access whereby the user manually connected a modem to the Internet provider. However, with the advent of ADSL, customers now have Internet access that is "always on." That is, it can simultaneously transmit voice and digital information on the same line.

Though ADSL enables customers to perform many of their Internet-related tasks easily, the nature of ADSL does slow down video and other transmissions that require a significant amount of bandwidth.

ADSL is "asymmetric" because it transmits data along phone lines unevenly -- that is, it allocates more bandwidth to the transmission of the customer's data than it does to the receipt of data because of the limited capacity and length of the phone line. The discrepancy is often acceptable to customers who download far more information than they upload.