The first communication systems which used electromagnetic means were digital: the telegraph was already in the middle of the 19th century. Even then played encoding, multiplexing, transmission line, and an important role in regeneration. After Bell in 1875, however, had invented the telephone and Edison carbon microphone in 1878, was the rise of the analogue transmission unstoppable. This emerged in the meantime world wide telephone network, which was fully optimized for the analog signal. The digital transmission was limited to telegraphy experiments after speech signals digitally using vibrating contacts transfer had failed.
It took until 1928 Nyquist fundamental theoretical principles about the transmission of digital signals through an analogue network could presentreren. This was the link between the bandwidth of one channel and the maximum number of characters per unit time that can be transmitted over it. This presentation was part of the reason for more attention to the digital transmission of analog information. In 1936 Reeves was therefore by the principles of pulse code modulation (PCM) developed. Here the analog signal in both time and amplitude sampling. The resulting digital signal is much less susceptible to noise and interference, which in the first instance especially for radio links of interest appeared.
The invention of the transistor in 1948 and the development of integrated circuits at the end of the fifties were quick and reliable circuitry with a small volume as possible.
In 1966 Kao and Hockham proposed optical fiber communications. After initially prohibitively high attenuation by improving the fiber was reduced to approximately 1dB/km, the fiber seen as the digital transportmdedium par excellence. Attenuation of 0.01 dB / km are theoretically possible, so thousands of kilometers can be bridged without regenerators.
The rapid development of microelectronics promoted not only the development of systems for digital transmission of analog information. The transport and processing of digital information (telematics) has expanded enormously. For the transport and routing of this digital information is an infrastructure. The worldwide network of computer networks is called the Internet.
The current technologies that form the basis for this infrastructure (dialup, broadband, Wi-Fi, satellite and 3G technology cell phones) all use the aforementioned digital communications.