Asymmetric Digital Subscriber Line (ADSL) is:
ADSL was designed to provide a dedicated, high-speed data connection for Internet/Intranet Access, using existing copper phone lines. This allows ADSL to work on over 60-80% of the phone lines existing in the U.S. without modification. Additionally, ADSL provides speeds approaching T1 (1.5Mbps), which are much greater than analog modems (56kbps) or ISDN (128kbps) services provided over the same type of line. ADSL is usually priced to be much less other dedicated digital services, and is expected to priced somewhere between T1 and ISDN services (including the ISDN usage charges).
The Telcos see ADSL as a competitive offering to the Cable Company's Cable Modems, and as such, are expected to provide competitive pricing/configuration offerings. Although Cable Modems are advertised as having 10-30Mbps bandwidth, they use a shared transmission medium with many other users on the same line, and therefore performance varies, perhaps greatly, with the amount of traffic and other users.
ADSL is positioned for Home and Small Office (SOHO) applications that require high-speed Internet Access. Since it also provides dedicated access, It can be used for interconnecting low-bandwidth servers to the Internet, and would provide a great access solution for 5-20 PCs in an Office location. It is also a great solution for those Linux power users that just want high speed access from home:-).
Digital Subscriber Line (DSL) provides a dedicated digital circuit from your home to the Telcos central office, using analog telephone line. DSL also provides a separate channel for voice phone conversations, which means analog calls (voice, fax. etc.) can be carried at the same time high-speed data is flowing across the line. DSL uses the frequency spectrum between 0kHz-4kHz for Analog Voice, and 4kHz-2.2MHz for data. xDSL is a generic acronym for a family of dedicated services, where the " x"stands for:
where Xbps/Ybps is X=Downstream Bit rate, Y=Upstream Bit rate
ADSL has to work over existing phone lines, which were designed 100 years ago, and were never designed for digital services (See the FAQ answers for more information). Also, ADSL is a new service, and all the providers are trying to find the right price/feature combinations that will make it in the market.
For the average user, the basic way of thinking about it is to segment the options into three categories:
Speed ranges from 384kbps-128kbps, Asymmetric
Speed ranges from 1.5Mbps-384kbps, Asymmetric
Speed ranges from +2.0Mbps-1.1kbps, Symmetric
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