Wikipedia
A modular connector is a type of electrical connector for cords and cables of electronic devices and appliances, such as in computer networking, telecommunication equipment, and audio headsets Modular connectors were originally developed for use on specific Bell System telephone sets in the 1960s, and similar types found use for simple interconnection of customer-provided telephone subscriber premises equipment to the telephone network The Federal Communications Commission (FCC) mandated in 1976 an interface registration system, in which they became known as registered jacks The convenience of prior existence for designers and ease of use led to a proliferation of modular connectors for many other applications
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