Even though the combination of radio and teletype (RATT) is generally no longer regarded as a modern means of information exchange, it is often the only available basis for data transmission due to its widespread use. Whether onboard a ship or in an embassy, teletype is still frequently used for sending text messages by radio. Texts are normally written in the internationally defined format ACP-127 (allied communication protocol). For transmission, the individual teletype characters are converted to 5-bit Baudot code. FSK (frequency-shift keying) is used to modulate the radio link. With data transmission rates between 50 and 600 baud, FSK may be comparatively slow but it is very resistant to interference.
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