Special Purpose Communication Devices

• Three types of multiplexers:

  • 1. Frequency division multiplexers (FDM) divide the circuit horizontally so that many signals can travel in the circuit simultaneously (channel = frequency range) (guardbands needed)
  • 2. Time division multiplexers (TDM) share a communication circuit among two or more terminals by

• having them take turns dividing the circuit vertically
• 3. Statistical Time Division Multiplexing (STDM) allows more terminals or computers to be connected to a circuit than FDM or TDM. It is based on a statistical analysis of the usage requirements of the circuits to be multiplexed.

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