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A registered jack (RJ) is a standardized physical interface--both jack construction and wiring pattern--for connecting telecommunications equipment (commonly, a telephone jack) or computer networking equipment to a service provided by a local exchange carrier or, sometimes, a long distance carrier. A telephone plug is a Plug which allows a Telephone to connect to the local telephone network Computer networking is the Engineering Discipline concerned with communication between Computer systems or devices Networking routers Local Exchange Carrier (LEC is a Regulatory term in Telecommunications for the local telephone company IXC redirects here For the IATA airport codes see Chandigarh Airport For Interexchange Point see Internet Exchange Point The standard designs for these connectors and their wiring are named RJ11, RJ14, RJ45, etc. RJ11 is a Physical interface often used for terminating Telephone wires RJ11 is a Physical interface often used for terminating Telephone wires The 8 Position 8 Contact (8P8C modular plugs and sockets are communications connectors These interface standards are most commonly used in North America, though some interfaces are used world-wide.

The physical connectors that registered jacks use are of the modular connector type, except RJ21X which is a 25-pair Amphenol connector. Modular connector is the name given to a family of Electrical connectors examples of which are pictured RJ-21 (or RJ21) is a Registered jack standard for a Modular connector using 50 conductors usually used to implement a 25- line For example, RJ11 uses a 6 pin 4 conductor (6P4C) modular plug and jack.

Left to right, RJ connectors: an eight-pin 8P8C plug (used for RJ49, RJ61 and others, but often called "RJ45" because of its outward semblance to the true RJ45), six-pin RJ25 plug, four-pin RJ14 plug (often also used instead of two-pin RJ11), and a four-pin handset plug (also popularly, though incorrectly, called "RJ22", "RJ10", or "RJ9"). The middle two can be plugged into the same standard six-pin jack, pictured.
Left to right, RJ connectors: an eight-pin 8P8C plug (used for RJ49, RJ61 and others, but often called "RJ45" because of its outward semblance to the true RJ45), six-pin RJ25 plug, four-pin RJ14 plug (often also used instead of two-pin RJ11), and a four-pin handset plug (also popularly, though incorrectly, called "RJ22", "RJ10", or "RJ9"). A transceiver is a device that has both a Transmitter and a receiver which are combined and share common circuitry or a single housing The middle two can be plugged into the same standard six-pin jack, pictured.

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Naming confusion

There is much confusion over these connection standards. The six-position plug and jack commonly used for telephone line connections may be used for RJ11, RJ14 or even RJ25, all of which are actually names of interface standards that use this physical connector. The RJ11 standard dictates a 2-wire connection, while RJ14 uses a 4-wire configuration, and RJ25 uses all six wires. The RJ abbreviations, though, only pertain to the wired jack (hence the name "Registered Jack"); it is commonplace but not strictly correct to refer to an unwired plug connector by any of these names.

Plugs and jacks of this type are often called modular connectors, which originally distinguished them from older telephone connectors, which were very bulky or wired directly to the wall and therefore not accommodating of modular systems. Basic principle A traditional landline telephone system also known as "plain old telephone service" (POTS, commonly handles both signaling and audio information A common nomenclature for modular connectors is e. g. "6P" to indicate a six-position modular plug or jack. Sometimes the nomenclature is expanded to indicate the number of positions that contain conductors. For example, a six-position modular plug with conductors in the middle two positions and the other four positions unused is called a 6P2C. RJ11 uses a 6P plug; furthermore, it often uses a 6P2C. (The connectors could be supplied more pins, but if more pins are actually wired, the interface is no longer an RJ11. )

Alternative terminologies are sometimes used, including 6×2 and 6/2.

Registered jacks were originally the subject of Bell System Universal Service Ordering Codes. The Bell System which was named for Alexander Graham Bell, the technologist popularly credited with the invention of the Telephone, was a Trademark and A USOC is a code one can use on an order for telephone service to specify the kind of service ordered. For example, to order a new telephone extension installed the subscriber might specify the USOC "RJ11W" in order to get a 6P2C jack for a conventional wall mounted single line telephone installed. People sometimes use "USOC" to refer to the service specification itself, though the USOC is just the name of it. With respect to registered jacks, the complete specification was registered (at one time with the US government) — hence the name. Though it's awkward to refer to a standard for a jack as a jack, it is nonetheless the conventional terminology. The registered jack is the type of physical interface and the USOC is a name for that type of physical interface.

It is important to note that a USOC does not always indicate precisely which connector to use.

Twisted pair

While the plugs are generally used with a flat cable (a notable exception being Ethernet twisted-pair cabling used with the 8P8C modular plug), the long cables feeding them in the building wiring and the phone network before them are normally twisted pair. The 8 Position 8 Contact (8P8C modular plugs and sockets are communications connectors Twisted pair Cabling is a form of wiring in which two conductors (two halves of a single circuit) are wound together for the purposes of canceling out Wiring conventions were designed to take full advantage of the physical compatibility ensuring that using a smaller plug in a larger socket would pick up complete pairs not a (relatively useless) two half pairs but here again there has been a problem. The original concept was that the centre two pins would be one pair, the next two out the second pair, and so on until the outer pins of an eight-pin connector would be the fourth twisted pair. Additionally, signal shielding was optimised by alternating the “live” (hot) and “earthy” (ground) pins of each pair. This standard for the eight-pin connector is the USOC-defined pinout, but the outermost pair are then too far apart to meet the electrical requirements of high-speed LAN protocols. Two variations known as T568A and T568B overcome this by using adjacent pairs of the outer four pins for the third and fourth pairs. TIA/EIA-568-B is a set of three Telecommunications standards from the Telecommunications Industry Association, a 1988 Offshoot of the EIA. TIA/EIA-568-B is a set of three Telecommunications standards from the Telecommunications Industry Association, a 1988 Offshoot of the EIA. The inner four pins are wired identically to RJ14. (See: Category 5 cable. Category 5 cable, commonly known as Cat 5, is a Twisted pair cable type designed for high signal integrity )

History and authority

Registered Jacks were introduced by the Bell System in the 1970s under a 1976 FCC order ending the use of protective couplers. The Bell System which was named for Alexander Graham Bell, the technologist popularly credited with the invention of the Telephone, was a Trademark and They replaced earlier, bulkier connectors. The Bell System issued specifications for the modular connectors and their wiring as Universal Service Ordering Codes (USOC), which were the only standard at the time.

When the US telephone industry was opened to more competition in the 1980s, the specifications were made a matter of US law, ordered by the Federal Communications Commission (FCC) and codified in the Code of Federal Regulations, 47 CFR 68, subpart F.

In January 2001, the FCC turned over responsibility for standardizing connections to the telephone network to a new private industry organization, the Administrative Council for Terminal Attachment (ACTA). The FCC removed Subpart F from the CFR and added Subpart G, which delegates the task to the ACTA. The ACTA published a standard called TIA/EIA-IS-968 which contained the information that was formerly in the CFR. The current version of that standard, called TIA-968-A, specifies the modular connectors at length, but not the wiring. Instead, TIA-968-A incorporates a standard called T1. TR5-1999 by reference to specify the wiring. Note that a Registered Jack name such as RJ11 identifies both the physical connectors and the wiring (pinout) of it (see above).

International use

The modular jack was chosen as a candidate for ISDN systems. In order to be considered, the connector system had to be defined under international standards. In turn this led to ISO 8877. Under the rules of the IEEE 802 standards project, international standards are to be preferred over national standards so the modular connector was chosen for IEEE 802. IEEE 802 refers to a family of IEEE standards dealing with Local area networks and Metropolitan area networks More specifically the IEEE 802 standards are 3i-1990, the original 10BASE-T twisted-pair wiring version of Ethernet. Ethernet is a family of frame -based Computer networking technologies for Local area networks (LANs

Registered jack types

The most familiar registered jack is probably the RJ11. This is a 6 position modular connector wired for one phone line, and is found in most homes and offices in North America for single line telephones.

RJ14 and RJ25 are also fairly common, using the same size connector as RJ11, but with two and three phone lines, respectively, connected.

Essentially all one, two, and three line telephones made today (2006) are meant to plug into RJ11, RJ14, or RJ25 jacks, respectively.

The true RJ45(S) is an extremely uncommon registered jack, but the name "RJ45" is also used quite commonly to refer to any 8P8C modular connector. The 8 Position 8 Contact (8P8C modular plugs and sockets are communications connectors Modular connector is the name given to a family of Electrical connectors examples of which are pictured

Many of the basic names have suffixes that indicate subtypes:

For example, RJ11 comes in two forms: RJ11W is a jack from which you can hang a wall telephone, while RJ11C is a jack designed to have a cord plugged into it. (You can plug a cord into an RJ11W as well, but it usually isn't as aesthetic as a cord plugged into an RJ11C).

Common types

Uncommon types

"Unofficial" (incorrect) plug names

These "RJ" names do not really refer to truly existing ACTA RJ types:

Other compatible Types

External links

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