Registered Jack - Glossary

USOC Registered Jacks



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Left to right, RJ connectors: an eight-pin RJ-45 plug, six-pin RJ-25 or RJ-12 plug, four-pin RJ-11 or RJ-14 plug, and a four-pin RJ-22 (RJ-10 or RJ-9) handset plug. The middle two plug into the same standard six-pin jack, pictured.

A registered jack (RJ) is a standardized physical interface for connecting telecommunications equipment (basically, a telephone jack). The standard designs for these connectors and their wiring are named RJ11, RJ14, RJ45, etc.

Numbering and pinouts were set forth by the Bell System in Universal Service Ordering Codes (USOCs), and were introduced in the 1970s by AT&T. They are also registered with the U.S. Federal Communications Commission (FCC), under 47 CFR §68.502.

A USOC is a code one can use on an order for telephone service to specify the kind of service ordered. For example, if you order a new telephone extension installed, you might specify the USOC "RJ11W" in order to get a 6P jack for a conventional wall-mounted single line telephone installed. People sometimes use "USOC" to refer to the service specification itself, though used literally, the USOC is just the name of it.