How DSL works

You may be surprised to learn that you're actually making a voice call every time your modem dials your local Internet service provider (or to anywhere you have it dial).

"Modem" is a portmanteau made from the words "MOdulate" and "DEModulate." The modem takes your digital information and turns it into an analog signal that is transmitted as a voice call over telephone lines. At the other end, a second modem turns the analog signal back into digital data.

Ever accidentally pick up the phone while a modem was on the line? You can hear the modem because the signal is being sent as a voice signal. Voice signals use the lowest frequencies that can travel across copper phone lines. Digital Subscriber Line technologies are based on using high frequency signals to transmit data over the same copper lines.

Like a regular modem, a DSL modem will translate digital data into an analog signal that will be sent across the copper lines. Unlike a regular modem, the DSL modem sends data over a different frequency set -- which means that the line can be used for data without interfering with, or precluding its use for, voice traffic.

That gives DSL a cost advantage. Current estimates are that DSL service will be around $50 a month. Heavy data users now generally pay more than that for two phone lines and an ISP.

-- C.J.F.

See also Microsoft primes many pumps to boost connectivity speeds

From THE COLE PAPERS, March 1998, Copyright © 1998, All Rights Reserved.