7 Asynchronous and synchronous data transmissionĬourses and textbooks in the field of data transmission as well as digital transmission and digital communications have similar content.ĭigital transmission or data transmission traditionally belongs to telecommunications and electrical engineering.This source coding and decoding is carried out by codec equipment.

It may also be an analog signal such as a phone call or a video signal, digitized into a bit-stream for example using pulse-code modulation (PCM) or more advanced source coding (analog-to-digital conversion and data compression) schemes. According to the most common definition of digital signal, both baseband and passband signals representing bit-streams are considered as digital transmission, while an alternative definition only considers the baseband signal as digital, and passband transmission of digital data as a form of digital-to-analog conversion.ĭata transmitted may be digital messages originating from a data source, for example a computer or a keyboard. The passband modulation and corresponding demodulation (also known as detection) is carried out by modem equipment. The messages are either represented by a sequence of pulses by means of a line code ( baseband transmission), or by a limited set of continuously varying wave forms ( passband transmission), using a digital modulation method. While analog transmission is the transfer of a continuously varying analog signal, digital communications is the transfer of discrete messages. The data are represented as an electromagnetic signal, such as an electrical voltage, radiowave, microwave, or infrared signal. Examples of such channels are copper wires, optical fibres, wireless communication channels, and storage media. Data transmission, digital transmission, or digital communications is the physical transfer of data (a digital bit stream) over a point-to-point or point-to-multipoint communication channel.

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