Types of DSL technology

ADSL (Asymmetric Digital Subscriber Line)

ADSL was originally designed by telephone companies to provide video-on-demand to compete with cable companies. This approach also turned out to be perfect for most users surfing the web. ADSL is faster on the download from the Internet, than uploading. Since most users send small requests on the net to receive large downloads of web pages and other information, this approach works well for must users.

Both Verizon and Qwest offer ADSL service.

RADSL (Rate Adaptive Asymmetric Digital Subscriber Line)

This service is like ADSL, but the hardware on each end is rate-adaptive. The DSL modem on each end of the copper phone wire synchronizes to the fastest possible speed for the quality of the phone line, and send data through at that speed (it's rate-adaptive). Factors like line quality, length of the copper wire, conditions on the wire, and even the weather will effect the actual throughput level you see for your DSL connection.

Both phone companies offer moderately priced RADSL connections. For these connections they offer up to the amount of speed specified in the offer. Your speed still depends on all of the limiting factors on your phone line.

Keep in mind that 'rate-adaptive' still works on your single phone line. It does not vary depending on the usage of others in your area (like cable). Your speed is only dependent on the quality of your phone line.

SDSL (Symmetric Digital Subscriber Line)

Symmetric DSL has the same throughput upload and download on the same connection.

IDSL (ISDN Digital Subscriber Line)

This service uses ISDN technology to provide DSL service to those that wouldn't ordinarily get it (usually because the copper to their house is too long for regular DSL). In some of these cases, IDSL will allow you to still get a dedicated DSL connection at 144kbps for a fraction of the price of ISDN.