RJ Full Form

RJ stands for Registered Jack.
It is a standard format of the telecommunication network interface used for connecting voice and data equipment. One of the main functionality of registered jacks is to connect different data equipment and telecommunication devices with services provided by telephone exchanges like long and short-exchange carrier.

History –
Registration interfaces were invented by the Bell System regulated by a 1976 Federal Communications Commission with respect to making an order of standard interface for customers and telephone exchange companies. The standard format of the modular jack was only created for integrated services digital network (ISDN) systems. But later, modular jacks were internationally standardized in IEEE 802.3i in 1990 due to its characteristics and capabilities.

Types Of RJ (Registered Jack) –

  • RJ-11 :
    This is a 4-wire or 6-wire telephone-type connector (Registered Jack) that connects telephone lines with wall plates. Primarily, it is located in houses and offices where old telephone-wired systems are connected with the ISP’s (Internet Service Providers) line.



  • RJ-11w :
    Here ‘w’ stands for wall mount. This one is an extended version of RJ-11 and is used with wall mount functionalities by establishing a bridged connection for one telephone line.

  • RJ-14 :
    This one is similar to RJ-11, but created for two lines and four lines respectively.

  • RJ-21 :
    This registered jack was designed with 50 conductors to implement 25 lines at a time. These are used in network areas with multiple switches and devices.

  • RJ-25 :
    This registered jack’s compatibility is too high and is often used for three telephones lines.

  • RJ-45 :
    This one is the best suited registered jack that has the ability to make the connection for both unshielded twisted-pair (UTP) and shielded twisted-pair (STP) cabling in star-topology of ethernet networks. It is one of the main registered jacks with an 8-wire telephone-type connector used with twisted-pair cabling for connecting computers and its lines, wall plates, patch panels, and other types of networking components.

  • RJ-48 :
    This jack is one of the best-registered jacks that use the same jack as RJ-45 but uses different types of pinning, where one pair of wires is used for transmitting signals, one pair for receiving signals, one pair for draining signals, and one pair is left unused. It comes in three different types such as RJ-48C for surface mount, RJ-48X for complex jack, and RJ-48S for a wall mount. Primarily it is used in LANs (Local Area Networks).

  • RJ-61 :
    This one is also similar to RJ-11, but used for termination of twisted-pair cables and uses an eight-pin modular connector.

Charateristics –

  • Have the capability to work with surfaces by mounting them with configuring interfaces.
  • They contain a number of potential contact positions and the actual number of contacts installed within these positions.
  • Have the feature of modularizing interfaces for telephone connections for one, two, and three-line service.
  • Can make cross-connection for two systems.

Advantages –

  • Registered jack is very easy to install.
  • Their reliability level is very high.
  • Their connection speed is higher with interfaces modularization.

Disadvantages –

  • They are only used for shortest networks.
  • They provide limited mobility.
  • They always require necessary wiring and equipments.

To know the difference between RJ45 and RJ11, refer.

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