How Is DSL Different From Dial-Up Phone Service?

When you talk into a telephone, it converts the analog signals from your voice into electrical pulses, and the receiving telephone converts the pulses back to analog. Data from a computer is digital and to connect it to the Internet via a telephone system, a modem must convert strings of digital information to electrical pulses. The phone company then has to convert these pulses back again. The electrical pulses from a modem use only a small portion of the frequency bandwidth of the telephone cables, limiting the speed that data can be transmitted.

If you have a DSL connection, the phone company transmits digital data directly to your computer via a DSL modem. The digital data occupies a far greater portion of the available bandwidth of the telephone lines because it can be transmitted in frequencies outside the audible range. The DSL and telephone signals have to be split, and this can be accomplished at the user end or at the phone company's offices. Most DSL lines are asymmetric, devoting a greater portion of the bandwidth to data traveling to the user (download) than that traveling from the user back to the phone company (upload).

You have to initiate a dial-up connection with your Internet service provider (ISP) by dialing a phone number. Because you are using the same band of frequencies as a telephone does, the line is unavailable for phone use while you are connected. Moreover, the narrow band of frequencies you are using limits the transmission rate to 56 kbps. A DSL connection, on the other hand, is always on, and the wide band of frequencies it employs makes download rates of up to 7 mbps possible. Upload rates don't usually exceed 400 kbps, but this is still 7 times faster than dial-up.

ISPs usually offer dial-up plans for a lower monthly fee than DSL and there is usually no set-up fee associated with a dial-up connection. Because using dialup is equivalent to using a telephone, you usually incur time charges. DSL isn't available to everyone who has a phone line. Unless your ISP has set up repeater stations, you are out of range if you are more than 3 1/2 miles from the phone company's office. Moreover, DSL transmission rates decrease with increasing distance from the ISP because of the physical limitations of the telephone wire carrying the signal.