Resumen de The sources and correction of errors in data transmission
A computer is often used to process data collected from, and distributed to, a comparatively large area, and in many applications speed is of such importance that electrical means of transmission are essential. For small quantities of data a switched communication channel will be appropriate, but for larger quantities a leased circuit may be justified.
The normal communication channels available in each case are either 50-baud (50 bits per second) telegraph circuits or else telephone circuits used alone or grouped to allow much higher speeds.
While the sources of data, and the means by wich data is processed, are not infallible, electrical transmission over existing communication channels introduces a greater liability to error.
The main links in the existing 50-baud telegraph circuits are voice-frequency telegraph channels assembled in groups of up to 24, each group being applied to a telephone circuit.
For the most part, the telephone circuits are themselves assembled by carrier methods into groups of 12 channels and supergroups of 60 channels, etc., and applied in hundreds, or even thousands, to coaxial cables.
The telephone channels and the broad-band carrier telephone systems are designed to carry the varying speech and signal powers which are applied to them, with a given statistical probability that they will not be overloaded for more than a given small fraction of time. During these shorts periods telegraph distortion may be high and some errors will be expected to occur.
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