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Chapter 19. First You Need a Modem > Smart Shopping for a Fast Connection - Pg. 176

First You Need a Modem 176 Chugging Along with Standard Modems Short for modulator demodulator, a modem converts incoming analog signals traveling through phone lines into digital signals that the PC can process. To send a signal, a modem converts the digital signal (consisting of 1s and 0s) from your PC into an analog (wave) signal that can be trans- mitted over phone lines. Modems transfer data at different speeds, commonly measured in bits per second (bps). The higher the number, the faster the modem can transfer data. Common rates include 28,800bps, 33,600bps, and 56,800bps. Because these modem speed numbers are becoming so long, manufacturers ab- breviate them; you'll commonly see speeds listed as 33.6Kbps. When they start dropping the bps and list something like 56K, you know it's really fast. Although you pay more for a higher transfer rate, you save time and decrease your phone bill by purchasing a faster modem. The bottom line is that if you're buying a standard modem, you should look for a 56Kbps modem; however, before you run out and buy one, you should know a few things: · 56K limits--56K pushes the limits of phone line communications. The phone company limits connection speeds to 53K, although there is some talk of raising the speed limit. You will rarely see data transfers at 56Kps. Expect a maximum speed of about 40­45Kbps, and that's only when your modem is receiving data. A 56K modem still sends data at 28.8­33.6Kbps because of other limitations, such as line noise. · x2 and 56Kflex and V.90--x2 and 56KFlex are competing 56K standards. x2 was developed by U.S. Robotics (now 3COM), and 56KFlex was developed by Hayes, Lucent Technologies, Rockwell, and others. These proprietary standards were developed before ITU (the International Telecommunication Union) defined the standard for 56K modems as V.90. If you buy a 56K modem, make sure it supports the V.90 standard. Don't get stuck with an old x2 or 56KFlex modem.