Key facts

  • 1928: Harry Nyquist stated the sampling-rate principle later used in the Nyquist theorem, linking reliable digital signalling to twice the highest sig...
  • 1948: Claude E. Shannon published "A Mathematical Theory of Communication", establishing channel capacity and the information-theory basis of modern c...
  • 1950: Richard W. Hamming introduced Hamming codes, a practical error-correcting method that can locate and correct single-bit errors under defined con...
  • 1962: AT&T's Bell 103 modem standardised 300 bit/s full-duplex data transmission over ordinary telephone lines, making modem communication a usable pu...
  • 1976: CCITT standard X.25 defined packet-switched wide-area data communication and became important for public data networks before the Internet era.

Key Points at a Glance

  1. 1

    1928: Harry Nyquist stated the sampling-rate principle later used in the Nyquist theorem, linking reliable digital signalling to twice the highest signal frequency.

  2. 2

    1948: Claude E. Shannon published "A Mathematical Theory of Communication", establishing channel capacity and the information-theory basis of modern communication systems.

  3. 3

    1950: Richard W. Hamming introduced Hamming codes, a practical error-correcting method that can locate and correct single-bit errors under defined conditions.

  4. 4

    1962: AT&T's Bell 103 modem standardised 300 bit/s full-duplex data transmission over ordinary telephone lines, making modem communication a usable public-network technology.

  5. 5

    1976: CCITT standard X.25 defined packet-switched wide-area data communication and became important for public data networks before the Internet era.

  6. 6

    1983: TCP/IP became the standard protocol suite of ARPANET, marking a key institutional shift from older network control methods to interoperable packet networking.

  7. 7

    1984, amended 1988: CCITT V.32 specified up to 9600 bit/s modem communication, showing how modulation and coding increased data rates on voice-grade telephone channels.

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Basic model, signals and data

Data communication is the transfer of data between two or more devices through a transmission medium. The standard model has five elements: sender, receiver, message, transmission medium and protocol. The sender generates data, the receiver interprets it, the medium carries the signal, and the protocol fixes the rules for format, timing, addressing, error control and response. A computer instructor exam often tests these terms directly because they separate communication hardware from communication rules.

Data is the meaningful information being sent; a signal is the physical representation of that data. Analog signals vary continuously with time, as in speech on a traditional telephone circuit. Digital signals take discrete levels, commonly represented as binary 0 and 1. Analog data can be sent as analog signals, digital data can be sent as digital signals, and conversion is possible in both directions by encoding, modulation, sampling and quantisation. In an RSSB classroom-network example, attendance data typed into a computer is digital data, while the electrical or radio waveform that carries it is the signal.

Remember this distinction: data is logical content, while the signal is the physical carrier.

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