Modems

• Modems (modulators / demodulators) are data communication equipment (DCE) devices that provide connections for computers into the Public Switched Telephone Network (PSTN). They convert (modulate) the digital signal generated by a computer into analog signal that can be transmitted over telephone line.

• The most important CCITT (ITU) standards are listed below:

  • V.22 1,200 bits/sec full duplex
  • V.22bis 2,400 bits/sec full duplex
  • V.28 defines circuits in RS-232
  • V.32 async / syn 4,800 and 9,600 bits/sec
  • V.32bis async / syn 14,400 bits/sec
  • V.32turbo 19,200 bits/sec
  • V.34 28.8 Kb/sec
  • V.34+ 33.6 Kb/sec
  • V.42 defines error check-in standard

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