Data transmission is, very generally speaking, the conveyance of any kind of information from one space to another. Historically this could be done by courier, a chain of bonfires or semaphores, and later by Morse code over copper wires.
In recent computer terms, it means sending a stream of bits or bytes from one location to another using any number of technologies to do so. Among them are copper wire, optical fibre, radio-link , laser, radio or infra-red light.
A related concept to data transmission is the data transmission protocol used to make the data transfer legible. Current protocols favour packet based communication.
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