DSL (digital subscriber line) technologies, often grouped under the term DSL, connect a computer to the Internet. DSL uses existing copper pair phone line wiring in conjunction with special hardware on the switch and user ends of the line. This special hardware allows for a continuous digital connection over the phone lines.

Since the connection is digital, DSL technology doesn't have a digital-to-analog conversion like traditional modems. It eludes voice audio spectrum frequency boundaries because it can use frequencies above the voice audio spectrum. This means you can use your phone while maintaining your Internet connection.

These different frequencies allow DSL to encode more data, and allow Internet connection speeds of up to 50 times faster than standard modems, and up to 12 times faster than an ISDN connection. Additionally, since DSL is not a bus technology, it offers more consistent bandwidth than cable modems in which multiple users share very high bandwidth media. However, distance limitations can affect the transmission rates or can be too great, rendering DSL infeasible. Also, the condition of your existing wiring can affect transmission rates.

The most commonly available DSL technology is ADSL, or asymmetric DSL. It is asymmetric in that it is designed to accommodate typical consumer Internet use, with much more data flowing toward the user (multimedia and text) than from the user (mostly keystrokes and mouse behavior). The downstream rate (receiving rate) varies from 1.5 to 9Mbps; the upstream rate (sending rate) varies from 16 to 640Kbps. These speeds depend greatly on the distance to the telephone company's central office.

DSL (Digital Subscriber Line) is an always-on internet connection that normally terminates in a socket on your wall, one that looks much like a phone socket. In the US, the socket is exactly a phone socket, and, for the popular residential DSL, (ADSL), the same house wiring does indeed carry both phone and data.



DSL is billed on a monthly basis, usually for a fixed price, and for the majority of providers it includes unlimited usage. In other words, whether you use it for email once a day, or you are a net addict and use it constantly, your bill is always the same.



Once you have a DSL line, you can use all the resources of the internet in the same way as you did from a regular modem and a dial-up account. The difference is now you can use them 24 hours a day with no connection delay, and usually (although not always) without a 'username' and 'password'. You need not worry about busy signals or any connection/disconnection process. 

The key advantage of DSL over a dial-up modem is speed. DSL is from several to dozens of times faster than a modem connection. A complex web page that could take up to a minute to finish loading at 56K can appear in just seconds over DSL.



   

Connection speed, reliability, and the 'always-on' nature of DSL are the main reasons it is so popular. For small businesses, DSL is also a great way to save money compared to pay per minute ISDN service, or T1 lines.