Modem

Stands for Modulator - demodulator, in accordance with the functions that perform modulation (change of binary pulses into analog signals) and demodulation. In data communications are always needed a pair of modems, each mounted on the transmitter and receiver.

  In determining the modem to be used there are some points to consider:

1. Data transmission rate (low, medium, high) 
2. Communication mode (simplex: one direction; half duplex: two directions alternately; Full duplex: two directions simultaneously) 
3. synchronization 
4. Modulation (Quadrature technique Aplitudo Modulation - Amplitude Modulation QAM belonging - AM, Frequency Shift Keying Techniques belonging to the Frequency Modulation - FM, and techniques that are categorized as Phase Shift Keying Phase Modulation - AM)

     Industry standards (standard internasionl secreted by the Consultative Committee Internationale de Telegraphique et Telephonique