- Asymmetric DSL (ADSL) - It is called 'asymmetric' because the download speed
is greater than the upload speed. ADSL works this way because most Internet
users download much more information than they upload.

- High bit-rate DSL (HDSL) - Providing transfer rates comparable to a T1 line,
HDSL receives and sends data at the same speed, but it requires two lines that are
separate from your normal phone line.

- Symmetric DSL (SDSL) - Like HDSL, this version receives and sends data at
the same speed. While SDSL also requires a separate line from your phone, it
uses only a single line instead of the two used by HDSL.

- Very high bit-rate DSL (VDSL) - An extremely fast connection, VDSL is
asymmetric, but only works over a short distance using standard copper phone

DSL Type Max. Send Speed Max. Receive Speed Max. Distance Lines Required Phone Support
ADSL 800 Kbps 8 Mbps 18,000 ft
(5,500 m)
1 Yes
HDSL 1.54 Mbps 1.54 Mbps 12,000 ft
(3,650 m)
2 No
SDSL 2.3 Mbps 2.3 Mbps 22,000 ft
(6,700 m)
1 No
VDSL 16 Mbps 52 Mbps 4,000 ft
(1,200 m)
1 Yes

- Voice-over DSL (VoDSL) - A type of IP telephony, VoDSL allows multiple phone
lines to be combined into a single phone line that also includes
data-transmission capabilities.