How to Install Modular Jacks by Yourself - AT&T Archives

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Modular jacks and plugs were developed for the phone system after 1968, to allow for easier hookups of external equipment. The modulars were developed in the next few years; made available starting in 1976. This film, from 1984, shows the customer how easy it was for each and every one of them—men and women—to install phones and phone equipment themselves, without having to bother the phone company.

The fundamental plug/jack model was patented by a cadre of Bell Labs engineers in 1973 (filed in 1972): Charles Krumreich, Edwin Hardesty, Albert Mulbarger, and Stephen Walden. A slight revision was filed shortly thereafter; that model is what became the common telephone plug and jack. It commonly is called the RJ-11 or RJ-14 (RJ standing for "registered jack"). The simplest plug contains two wires, which represents one phone line. More commonly today, even the simplest contain six. The RJ-11 is by far the most common phone connection in the world. Only a handful of countries don't use this jack system at all. An awesome chart of all the modular jack systems around the world is at phone-jack.org; it reflects both the politics and technological growth of countries during the 20th century.

The wire pairs are arranged in what is called a "tip and ring" formation, which corresponds with the wiring in the bell system when phones were connected via the operator—the "tip" refers to the tip of the operator's plug connection, the "ring" is the ring around the plug. Green and Red were "tip and ring" for the first pair, Black and Yellow for the second.

A modern ethernet cable uses a similar design, but includes more wires within the plug and jack.

Footage Courtesy of AT&T Archives and History Center, Warren, NJ