In order to transmit the fax and modem data, the signals must be processed in such a way that they are adapted and ruggedized for the transmission over noisy and disturbed telephone lines. Transmit and reception processing takes place in devices called modems – a combination of “modulator” and “demodulator”. The properties of various modems are standardized through ITU (International Telecommunications Union) V-series recommendations. Fax standards are laid down in a number of T-series recommendations.