Can You Run DSL & Dial-up on the Same Line?

by Richard Gaughan
For many people, dial-up service might as well be from the Stone Age, but 6 percent of Americans still depend on it.

For many people, dial-up service might as well be from the Stone Age, but 6 percent of Americans still depend on it.

Digital subscriber line service and dial-up connections are both methods for connecting your home computer to the Internet. In today's world, Internet connection is becoming a necessity, rather than a luxury. Websites are not only an essential for today's business, but they are becoming more graphics, audio and video intensive. Still, according to the FCC, 6 percent of Americans have dial-up service as their home Internet connection. Some people looking to upgrade, but not certain of the implications of the switch, may want to run DSL and dial-up on the same line. It can be done.

Why Have Both?

DSL and dial-up both do the same thing --- they both transmit signals between your computer and the rest of the world. If you're making the transition from dial-up to DSL, you might want to wait to get rid of your dial-up until after you check out your DSL. The only other reason to have both would be if you have an old computer without high-speed capabilities and you also have a newer computer, and you want to use both. Whichever the situation, once you experience DSL speeds it's likely you'll find dial-up frustratingly slow.


If you want to have both services, you will need to pay for both. DSL and other broadband costs are rapidly dropping, and dial-up costs can be even less than ten dollars a month, so it won't be too taxing to maintain both services, but it will be an added cost.

Speed Limitations

The speed of a signal is limited by the modulation of the source and the bandwidth of the communications line --- about 56 Kbps for dial-up.

A computer's communication rate has two limitations: the modulation rate and the data line bandwidth. Dial-up service uses an electronic modem to modulate the signal to be put on a phone line. No matter how fast the signal gets modulated, however, it's still limited by the phone line. Copper phone lines can't handle a very fast data rate, so dial-up service is limited to maybe 56 Kbps. At least, that was the thinking for a long time.

DSL Changes Things

DSL uses those same copper phone lines, but in a new way. Instead of sending a signal through the copper phone lines, DSL sends its signal just along the surface of the copper wires. It's a tiny change, but it makes a big difference. Because the signal doesn't need to push electrons through the whole diameter of the wire, a DSL signal can be modulated much faster. It uses the same wires, but in a different way. That's why a DSL line requires a splitter at the connection point. Part of the signal is transmitted the traditional way and part the new way, and the splitter separates those two.

Using DSL and Dial-Up

Because DSL and dial-up signals are sent so differently, it's possible to use both at the same time. Where the DSL splits off, one line will be labeled "DSL" and the other "phone." The frequencies for DSL will be on the DSL portion of the line, while the regular telephone frequencies will be on the other portion. Because dial-up uses the traditional telephone frequencies, you can plug your dial-up connection into the phone plug at the same time as your DSL connection is using the DSL plug. Both signals can get sent back and forth through the phone lines without interfering with each other.

About the Author

First published in 1998, Richard Gaughan has contributed to publications such as "Photonics Spectra," "The Scientist" and other magazines. He is the author of "Accidental Genius: The World's Greatest By-Chance Discoveries." Gaughan holds a Bachelor of Science in physics from the University of Chicago.

Photo Credits

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