DSL
Stands for "Digital Subscriber Line." It is medium for transferring data over regular phone lines and can be used to connect to the Internet. However, like a cable modem, a DSL circuit is much faster than a regular phone connection, even though the wires it uses are copper like a typical phone line. In order for DSL to be installed it must be provisioned across a standard telephone line.
Types of DSL
ADSL- Asymmetric Digital Subscriber Line
An asymmetric DSL (ADSL) connection allows download speeds of up to about 1.5 megabits (not megabytes) per second, and upload speeds of 128 kilobits per second. That is why it is called ADSL and not just DSL (because of the asymmetric speeds). In other words different speeds up and down with the upload speed being slower.
SDSL- Symmetric Digital Subscriber Line
There is also a "Symmetric Digital Subscriber Line" (SDSL) which is similar to ADSL, but allows data transfer speeds of 384 Kilobits per second in both directions therefore it is symmetrical. In other words users experience the same speed when uploading and downloading from the internet.
IDSL- Internet Digital Subscriber Line
Internet Digital Subscriber Line, unlike dial-up, is a connection that is always connected to the Internet. On average, connectivity with IDSL is twice the speed of a regular dial-up connection. IDSL service is based upon Integrated Services Digital Network (ISDN) technology. ISDN is a system of digital phone connections that allows data to be transmitted simultaneously across the globe using end-to-end digital connectivity (IDSN allows multiple digital channels to be operated at the same time through the same regular phone lines used for analog lines).
