Page "Data transmission" Paragraph 25

Data ( mainly but not exclusively informational ) has been sent via non-electronic ( e. g. optical, acoustic, mechanical ) means since the advent of communication.

Analog signal data has been sent electronically since the advent of the telephone.

However, the first data electromagnetic transmission applications in modern time were telegraphy ( 1809 ) and teletypewriters ( 1906 ), which are both digital signals.

The fundamental theoretical work in data transmission and information theory by Harry Nyquist, Ralph Hartley, Claude Shannon and others during the early 20th century, was done with these applications in mind.