I use this as a reminder.

DSL Notes

DSL (digital subscriber line) typically runs over the same pair of wires that you use for the landline telephone. It is distance sensitive when it comes to speeds and availability. Closer to the telephone companies Central Office (CO) the better things will be.

A splitter is used at the wall jack to literally split the frequencies - one for voice and the other for data (DSL service) - to enable them both to run on the same pair of wires. A filter is usually built in there as well to prevent the hissing noise due to high frequencies.

Naked DSL is DSL without the telephone service. 

Asymmetric DSL - upload and download speeds are different. This is by far more common.

Symmetric DSL - upload and download speeds are the same.