In this tutorial, we will teach you how the ADSL (more commonly known simply as “DSL” in the U.S.) connection works, including the latest ADSL2 and ADSL2+ technologies.
Here is a snippet:
"ADSL (Asymmetric Digital Subscriber Line) is one of the most popular technologies for Internet connection, using the infrastructure of your local telephone company. There are several types of DSL (a.k.a. xDSL) connections, such as VDSL, with ADSL being the most popular one in most countries. Its name comes from the fact that its download speed is higher than its upload speed, hence classified as asymmetrical. A symmetrical connection is one where the download and the upload speeds are the same."