There are lots of variations in DSL technology -- many of them address DSL's distance limitations in one way or another. Other types of DSL include:
- Very high bit-rate DSL (VDSL) - This is a fast connection, but works only over a short distance. It is capable of handling Internet access, HDTV and on-demand services at rates of 52 Mbps downstream and 12 Mbps upstream.
- Symmetric DSL (SDSL) - This connection, used mainly by small businesses, doesn't allow you to use the phone at the same time, but the speed of receiving and sending data is the same.
- Rate-adaptive DSL (RADSL) - This is a variation of ADSL, but the modem can adjust the speed of the connection depending on the length and quality of the line.
- ISDN DSL (IDSL) - This is a combination of the Integrated Services Digital Network (ISDN) and DSL technology. ISDN was the solution to dial-up Internet -- it allowed voice, text graphics, video and other data to share one telephone line. This made it possible to talk on the phone and use the Internet at the same time. IDSL is faster than ISDN connections but slower than DSL. It can travel a longer distance of 5 to 6 miles, so it is usually a good option for people who can't get DSL in their area.
- Universal DLS (Uni-DSL) - This emerging technology, developed by Texas Instruments, is backwards compatible with all existing versions of DSL. It offers somewhat of a middle ground between ASDL and VDSL -- at longer distances, it can reach the speeds of ASDL, but it can provide greater speeds than VDSL at shorter distances. In some locations, Uni-DSL can provide four times the amount of speed as VDSL.
Alternatives to DSL
With DSL's distance limitation and lower availability, what are some other options? There are two major alternatives to DSL -- cable and wireless.
Cable and DSL are the two big rivals in the world of broadband. Cable isn't limited by distance like DSL -- cable wires reach most neighborhoods, and signal strengths don't weaken over long distances. While DSL allows you to use the telephone and Internet simultaneously, cable lets users watch television and surf the Internet at the same time. Many cable companies are also beginning to bundle services with cable TV, Internet and digital telephone on one bill. Although cable and DSL speeds are about the same, the one disadvantage with cable is bandwidth -- connection speeds can slow down if too many people are using a cable service at the same time.
A new technology, known as WiMax or 802.16, looks to combine the benefits of broadband and wireless. WiMax will provide high-speed wireless Internet over very long distances and will most likely provide access to large areas such as cities. WiMax technology will be available in most American cities in 2008.
To learn more about DSL and other topics, read on to the next page.