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  PC-Net's PC News - August, 1998
Don Watkins

Modem Math 102: 56K Is a One-way Mirror

By Don Watkins



August 1998--You have installed your shiny new 56K modem, and you are now enjoying increased download speeds. Your next step is to connect it to a friend's 56K modem.

OK, where did the speed increase go?

56K depends on the special relationship that the Internet service provider (ISP) has with your local telephone company, and how the telephone company and your modem operate. Modems are analog devices. They send and receive information as a series of sound waves. If you were really wiggy and cool, you could get on your telephone handset and make noises like a modem does and "talk" to another modem. Note that I'm not aware of a human that has actually done this, although I have some friends about whom I'm not so sure.

Computers, on the other hand, are digital devices. They deal with zeros and ones, not sound waves. The modem's job is to convert the signals from digital (the computer end) to analog (the telephone end). The term "modem" is derived from the terms "Modulation/De-Modulation," which means converting from analog to digital and back again.

Modern telephone switching equipment is now able to handle digital signals directly and this makes 56K possible. The finer details of this technology are complex but the engineers tell us that the best we can get from the copper wire and the older switching equipment is 33.6K. To go faster, some of the conversions from analog to digital and back must be removed. That's exactly what happens with 56K. The ISP and the telephone company get together and build a digital link between their two offices. This means the only conversion from digital to analog occurs when the signal is sent to your phone line.

If you have been having problems getting a 56K connection to work, you will want to test your line to make sure there is only one analog-to-digital conversion happening. The folks at 3COM have a test that you can run to check your line. Visit 3COM's site at for complete details.

When you connect with your friend, you have more than one analog/digital conversion in the connection and one at your friend's end. This is why 56K doesn't work between two 56K modems.

Next month, we'll examine some other methods of sending information from one system to another.


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