Tech Talk: DSL Quiz

A DSL modem uses the same telephone wires you use for your regular telephone service.

The main problem with ADSL is that the speed of your service depends on how far away you are from the local telephone switching office. But you can use a phone and an ADSL modem at the same time with no problem, and most of the time there's no need to do any rewiring with a DSL system.

Asymmetric DSL lines (ADSL) dedicate more bandwidth for downloads than uploads. Most users are downloading far more information than they upload to the Internet, so it makes sense to prioritize download speed over upload speed.

The discrete multitone (DMT) standard is the official standard for ADSL. It divides data into 247 separate channels, each of which is 4 kilohertz wide.

Low-pass filters block signals over a certain frequency. Human conversations take place below 4 KHz, whereas ADSL signals are above 4KHz. By blocking all signals over 4 KHz, a low-pass filter prevents ADSL from interfering with a telephone signal.

A DSLAM aggregates customer connections and links them to a high-capacity Internet connection.

ADSL service can extend 18,000 feet (5,460 meters) before the speed and quality of service dips below acceptable levels.

A CAP system divides telephone signals into three bands of frequencies. The first band ranges from 0 KHz to 4 KHz and covers all telephone communication. The second band ranges from 25 KHz to 160 KHz and carries all uploads to the system. The third begins at 240 KHz and carries all downloading signals.

DSL modems are transceivers -- they send and receive signals to and from the user's computer and the Internet service provider.

Most DSL modems connect to computers using either a USB cable or an Ethernet cable.