Registered Jacks

Phone jacks are known as Registered Jacks. Registered Jacks are approved and authorized by the Federal Communications Commission. The naming convention for Registered Jacks is RJ-xx, where xx is a two digit number. The two digit number indicates the type of physical interface and the area of its application. For example: RJ11, RJ14, and RJ25 are used for terminating phone lines, whereas RJ45 is used in computer networking.

RJ11 connector

The RJ11 is the most common phone jack that is in use today. RJ11 connectors are used to terminate phone lines, and are typically deployed with single line POTS (Plain Old Telephone Service) telephone jacks.

The diagram below displays the RJ11 connector.

Figure 1: RJ11 connector


The RJ11 connector is usually encased in plastic and is modular in design. Modular design indicates that the components involved (telephone jack and connector) can be plugged with each other, rather than being hard-wired.

The RJ11 connector uses the 6P4C (six position, 4 contacts) wiring standard. 6P4C indicates that the connector has six positions, out of which only four positions have contacts. These four contacts have two wires attached to them. This kind of wiring standard for modular connectors is utilized to ensure that the plug fits perfectly.

RJ11 connector pinout

The table below displays the RJ11 connector pinout:

Table 1: RJ11 connector pinout




Pin 1


Pin 2


Pin 3


Pin 4



Pin 5

Pin 6

Pin three and four are used for ‘Tip’ and ‘Ring’ wires of the telephone line. Tip is the ground wire (positive), and Ring is the battery (negative) wire of a phone circuit.

The additional conductors can be used for other functionalities such as a ground for selective ringers, low voltage power for a dial light, and so on.

At the advent of the information age, and with the creation of the World Wide Web, dial-up Internet access was the prescribed form of internet access. It utilized the same system of RJ11 phone jacks and connectors, as dial-up Internet access was via telephone lines.

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