A registered jack (RJ) is a standardized

telecommunication Telecommunication is the transmission of information by various types of technologies over wire, radio, optical, or other electromagnetic systems. It has its origin in the desire of humans for communication over a distance greater than that fe ...

network interface Network interface may refer to: * Network interface controller, a computer hardware component that connects a computer to a computer network * Network interface device, a device that serves as the demarcation point between a telephone carrier's loc ...

for connecting voice and data equipment to a service provided by a local exchange carrier or

long distance carrier An interexchange carrier (IXC), in U.S. legal and regulatory terminology, is a type of telecommunication Telecommunication is the transmission of information by various types of technologies over wire, radio, optical, or other electromagn ...

. Registration interfaces were first defined in the ''Universal Service Ordering Code'' (USOC) system of the

Bell System The Bell System was a system of telecommunication companies, led by the Bell Telephone Company and later by the American Telephone and Telegraph Company (AT&T), that dominated the telephone services industry in North America for over one hundr ...

in the United States for complying with the registration program for customer-supplied telephone equipment mandated by the

Federal Communications Commission The Federal Communications Commission (FCC) is an independent agency of the United States federal government that regulates communications by radio, television, wire, satellite, and cable across the United States. The FCC maintains jurisdiction ...

(FCC) in the 1970s. They were subsequently codified in title 47 of the

Code of Federal Regulations In the law of the United States, the ''Code of Federal Regulations'' (''CFR'') is the codification of the general and permanent regulations promulgated by the executive departments and agencies of the federal government of the United States. ...

Part 68. Registered jack connections began to see use after their invention in 1973 by

Bell Labs Nokia Bell Labs, originally named Bell Telephone Laboratories (1925–1984), then AT&T Bell Laboratories (1984–1996) and Bell Labs Innovations (1996–2007), is an American industrial research and scientific development company owned by mult ...

. The specification includes physical construction, wiring, and signal semantics. Accordingly, registered jacks are primarily named by the letters ''RJ'', followed by two digits that express the type. Additional letter suffixes indicate minor variations. For example, RJ11, RJ14, and RJ25 are the most commonly used interfaces for telephone connections for one-, two-, and three-line service, respectively. Although these standards are legal definitions in the United States, some interfaces are used worldwide. The connectors used for registered jack installations are primarily the

modular connector A modular connector is a type of electrical connector for cords and cables of electronic devices and appliances, such as in computer networking, telecommunication equipment, and audio headsets. Modular connectors were originally developed fo ...

and the 50-pin

miniature ribbon connector The micro ribbon or miniature ribbon connector is a common type of electrical connector for a variety of applications, such as in computer and telecommunications equipment having many contacts. The connector contains two parallel rows of ...

. For example, RJ11 uses a six-position two-conductor connector (

6P2C A modular connector is a type of electrical connector for cords and cables of electronic devices and appliances, such as in computer networking, telecommunication equipment, and audio headsets. Modular connectors were originally developed for ...

), RJ14 uses a six-position four-conductor (

6P4C A modular connector is a type of electrical connector for cords and cables of electronic devices and appliances, such as in computer networking, telecommunication equipment, and audio headsets. Modular connectors were originally developed for ...

) modular jack, while RJ21 uses a 25-pair (50-pin) miniature ribbon connector.

Naming standard

The registered jack designations originated in the standardization process of telephone connections in the Bell System in the United States, and describe application circuits and not just the physical geometry of the connectors. The same modular connector type may be used for different registered jack applications. Modular connectors were developed to replace older telephone installation methods that used hardwired cords or bulkier varieties of

telephone plug A telephone jack and a telephone plug are electrical connectors for connecting a telephone set or other telecommunications apparatus to the telephone wiring inside a building, establishing a connection to a telephone network. The plug is inserted ...

s. Strictly, ''Registered Jack'' refers to both the female physical connector (

) and specific wiring patterns, but the term is often used loosely to refer to modular connectors regardless of wiring, gender, or use, commonly for telephone line connections, but also for

Ethernet over twisted pair Ethernet over twisted-pair technologies use twisted-pair cables for the physical layer of an Ethernet computer network. They are a subset of all Ethernet physical layers. Early Ethernet used various grades of coaxial cable, but in 1984, Sta ...

, resulting in confusion over the various connection standards and applications. For example, the six-position physical connector, plug and jack, is identically dimensioned and inter-connectable, whether it is wired for one, two, or three lines. These are the RJ11, RJ14, and RJ25 interfaces. The RJ standards designations only pertain to the wiring of the (female) jacks, hence the name ''Registered Jack''. It is commonplace, but not strictly correct, to refer to the unwired connectors or the (male) plugs by these names. The nomenclature for modular connectors is based on the number of contact positions and the number of wires connected. ''6P'' indicates a six-position modular plug or jack. A six-position modular plug with conductors in only the middle two positions is designated 6P2C; 6P4C has four conductors in the middle positions, and 6P6C has all six equipped.

History and authority

Registration interfaces were created by the Bell System under a

order for the standard

interconnection In telecommunications, interconnection is the physical linking of a carrier's network with equipment or facilities not belonging to that network. The term may refer to a connection between a carrier's facilities and the equipment belonging to ...

between telephone company equipment and

customer premises equipment In telecommunications, a customer-premises equipment or customer-provided equipment (CPE) is any terminal and associated equipment located at a subscriber's premises and connected with a carrier's telecommunication circuit at the demarcation poi ...

. These interfaces used newly standardized jacks and plugs, primarily based on miniature

s. The wired communications provider (telephone company) is responsible for delivery of services to a minimum (or main) point of entry (

MPOE In telephony, the demarcation point is the point at which the public switched telephone network ends and connects with the customer's on-premises wiring. It is the dividing line which determines who is responsible for installation and maintena ...

). The MPOE is a utility box, usually containing surge protective circuitry, which connects the wiring on the customer's property to the communication provider's network. Customers are responsible for all jacks, wiring, and equipment on their side of the MPOE. The intent was to establish a universal standard for wiring and interfaces, and to separate ownership of in-home (or in-office) telephone wiring from the wiring owned by the service provider. In the

, following the

Communications Act of 1934 The Communications Act of 1934 is a United States federal law signed by President Franklin D. Roosevelt on June 19, 1934 and codified as Chapter 5 of Title 47 of the United States Code, et seq. The Act replaced the Federal Radio Commission with ...

, the telephone companies owned all telecommunications equipment and they did not allow

of third-party equipment. Telephones were generally hardwired, but may have been installed with Bell System connectors to permit portability. The legal case ''

Hush-A-Phone v. United States ''Hush-A-Phone v. United States'', 238 F.2d 266 (D.C. Cir. 1956) was a seminal ruling in United States telecommunications decided by the D.C. Circuit Court of Appeals. Hush-A-Phone Corporation marketed a small, cup-like device which mounted on th ...

'' (1956) and the

's (FCC) ''

Carterfone The Carterfone is a device invented by Thomas Carter. It manually connects a two-way radio system to the telephone system, allowing someone on the radio to talk to someone on the phone. This makes it a direct predecessor to today's autopatch. ...

'' (1968) decision brought changes to this policy, and required the Bell System to allow some interconnection, culminating in the development of registered interfaces using new types of miniature connectors. Registered jacks replaced the use of protective couplers provided exclusively by the telephone company. The new modular connectors were much smaller and cheaper to produce than the earlier, bulkier connectors that were used in the Bell System since the 1930s. The Bell System issued specifications for the modular connectors and their wiring as ''Universal Service Order Codes'' (USOC), which were the only standards at the time. Large customers of telephone services commonly use the USOC to specify the interconnection type and, when necessary, pin-assignments, when placing service orders with a network provider. When the U.S. telephone industry was reformed to foster competition in the 1980s, the connection specifications became federal law, ordered by the

FCC The Federal Communications Commission (FCC) is an independent agency of the United States federal government that regulates communications by radio, television, wire, satellite, and cable across the United States. The FCC maintains jurisdiction ...

and codified in the Code of Federal Regulations (CFR),

Title 47 CFR Part 68 'Title 47 CFR Part 68'' is a section of the Code of Federal Regulations of the United States that regulate the direct electrical connection of telecommunications equipment and customer premises wiring with the public switched telephone network, cert ...

, Subpart F,FCC 47 CFR Part 68 ''Connection of Terminal Equipment to the Telephone Network''
, Section 68.502 superseded by T1.TR5-1999 superseded by T1.TR5-1999. In January 2001, the FCC delegated responsibility for standardizing connections to the telephone network to a new private industry organization, the

Administrative Council for Terminal Attachments A registered jack (RJ) is a standardized telecommunication network interface for connecting voice and data equipment to a service provided by a local exchange carrier or long distance carrier. Registration interfaces were first defined in the ...

(ACTA). For this delegation, the FCC removed Subpart F from the CFR and added Subpart G. The ACTA derives its recommendations for terminal attachments from the standards published by the engineering committees of the

Telecommunications Industry Association The Telecommunications Industry Association (TIA) is accredited by the American National Standards Institute (ANSI) to develop voluntary, consensus-based industry standards for a wide variety of Information and Communication Technologies (Inform ...

(TIA). ACTA and TIA jointly published the standard TIA/EIA-IS-968,TIA-968-A
o
tia-eia-is-968
documents o

specifications from th
Administrative Council for Terminal Attachments
, section 6.2 in particular replacing the CFR information. TIA-968-A, the current version of that standard, details the physical aspects of modular connectors, but not the wiring. Instead, TIA-968-A incorporates the standard T1.TR5-1999, "Network and Customer Installation Interface Connector Wiring Configuration Catalog",T1.TR5-1999
Network and Customer Installation Interface Connector Wiring Configuration Catalog by reference. With the publication of TIA-968-B, the connector descriptions have been moved to TIA-1096-A. A registered jack name, such as RJ11, still identifies both the physical connectors and the wiring (pinout) for each application.

Types

The most widely implemented registered jack in telecommunications is the RJ11. This is a modular connector wired for one telephone line, using the center two contacts of six available positions. This configuration is also used for single-line telephones in many countries other than the United States. It may also use a 6P4C connector, to use an additional wire pair for powering lamps on the telephone set. RJ14 is similar to RJ11, but is wired for two lines and RJ25 has three lines. RJ61 is a similar registered jack for four lines, but uses an 8P8C connector. The RJ45S jack is rarely used in telephone applications but a standard version of the

8P8C modular connector A modular connector is a type of electrical connector for cords and cables of electronic devices and appliances, such as in computer networking, telecommunication equipment, and audio headsets. Modular connectors were originally developed for ...

used by RJ45S is used in Ethernet networks and the connector is often referred to as RJ45 in this context. Many of the basic names have suffixes that indicate subtypes: *C: flush-mount or surface mount *F: flex-mount *W: wall-mount *L: lamp-mount *S: single-line *M: multi-line *X: complex jack For example, RJ11 comes in two forms: RJ11W is a jack from which a wall telephone can be hung, while RJ11C is a jack designed to have a cord plugged into it. A cord can be plugged into an RJ11W as well.

RJ11, RJ14, RJ25 wiring

All of these registered jacks are described as containing a number of potential

contact Contact may refer to: Interaction Physical interaction * Contact (geology), a common geological feature * Contact lens or contact, a lens placed on the eye * Contact sport, a sport in which players make contact with other players or objects * ...

positions and the actual number of contacts installed within these positions. RJ11, RJ14, and RJ25 all use the same six-position

, thus are physically identical except for the different number of contacts (two, four and six respectively) allowing connections for one, two, or three telephone lines respectively. Cords connecting to an RJ11 interface require a 6P2C connector. Nevertheless, cords sold as RJ11 often use 6P4C connectors (six position, four conductor) with four wires. Two of the six possible contact positions connect tip and ring, and the other two conductors are unused. The conductors other than the two central tip and ring conductors are in practice variously used for a second or third telephone line, a

ground Ground may refer to: Geology * Land, the surface of the Earth not covered by water * Soil, a mixture of clay, sand and organic matter present on the surface of the Earth Electricity * Ground (electricity), the reference point in an electrical c ...

for selective ringers, low-voltage power for a dial light, or for anti-tinkle circuitry to prevent

pulse dialing Pulse dialing is a signaling technology in telecommunications in which a direct current local loop circuit is interrupted according to a defined coding system for each signal transmitted, usually a digit. This lends the method the often used name ...

phones from sounding the bell on other extensions.

Pinout

Observing the male connector from the cable opening, with prong facing downward, the pins are numbered 1–6, left to right:

Provisioning of power

Some telephones such as the Western Electric

Princess Princess is a regal rank and the feminine equivalent of prince (from Latin ''princeps'', meaning principal citizen). Most often, the term has been used for the consort of a prince, or for the daughter of a king or prince. Princess as a subst ...

and

Trimline telephone The Trimline telephone is a series of telephones that was produced by Western Electric, the manufacturing unit of the Bell System. These telephones were first introduced in 1965 and are formally referred to as the ''No. 220 Hand Telephone ...

models require additional power (~6 V AC) for operation of the incandescent dial light. This power is delivered to the telephone set from a transformer by the second wire pair (pins 2 and 5) of the 6P4C connector.

RJ21

RJ21 is a registered jack

standard Standard may refer to: Symbols * Colours, standards and guidons, kinds of military signs * Standard (emblem), a type of a large symbol or emblem used for identification Norms, conventions or requirements * Standard (metrology), an object th ...

using a

with contacts for up to fifty conductors. It is used to implement connections for up to 25

lines Line most often refers to: * Line (geometry), object with zero thickness and curvature that stretches to infinity * Telephone line, a single-user circuit on a telephone communication system Line, lines, The Line, or LINE may also refer to: Arts ...

, or circuits that require many wire pairs, such as used in the

1A2 key telephone system The 1A2 Key Telephone System is a business telephone system developed and distributed by the Western Electric Company for the Bell System. The 1A2 Key Telephone System is a modular system that provided flexible solutions for a variety of telepho ...

. The

of this interface is also known as a 50-pin telco connector, CHAMP(AMP), or ''Amphenol'' connector, the latter being a

genericized trademark A generic trademark, also known as a genericized trademark or proprietary eponym, is a trademark or brand name that, because of its popularity or significance, has become the generic term for, or synonymous with, a general class of products or ...

, as

Amphenol Amphenol Corporation is a major producer of electronic and fiber optic connectors, cable and interconnect systems such as coaxial cables. Amphenol is a portmanteau from the corporation's original name, American Phenolic Corp. History Amphenol ...

was a prominent

manufacturer Manufacturing is the creation or production of goods with the help of equipment, labor, machines, tools, and chemical or biological processing or formulation. It is the essence of secondary sector of the economy. The term may refer to a ran ...

of these at one time. A cable color scheme, known as

even-count color code The 25-pair color code, originally known as even-count color code, is a color code used to identify individual conductors in twisted-pair wiring for telecommunications. Color coding With the development of new generations of telecommunication cab ...

, is determined for 25 pairs of conductors as follows: For each ring, the primary, more prominent color is chosen from the set blue, orange, green, brown, and slate, in that order, and the secondary, thinner stripe color from the set of white, red, black, yellow, and violet colors, in that order. The tip conductor color scheme uses the same colors as the matching ring but switches the thickness of the primary and secondary colored stripes. Since the sets are ordered, an orange (color 2 in its set) with a yellow (color 4) is the color scheme for the 4·5 + 2 − 5 = 17th pair of wires. If the yellow is the more prominent, thicker stripe, then the wire is a tip conductor connecting to the pin numbered 25 + the pair #, which is pin 42 in this case. Ring conductors connect to the same pin number as the pair number. A conventional enumeration of wire color pairs then begins blue (and white), orange (and white), green (and white) and brown (and white), which subsumes a color-coding convention used in cables of 4 or fewer pairs (8 wires or less) with 8P and 6P connectors. Dual 50-pin ribbon connectors are often used on

punch block A punch-down block (also punchdown block, punch block, punchblock, quick-connect block and other variations) is a type of electrical connection often used in telephony. It is named because the solid copper wires are "punched down" into short open ...

s to create a

breakout box A breakout box is a piece of electrical test equipment used to support integration testing, expedite maintenance, and streamline the troubleshooting process at the system, subsystem, and component-level by simplifying the access to test signals. B ...

for

private branch exchange A business telephone system is a multiline telephone system typically used in business environments, encompassing systems ranging in technology from the key telephone system (KTS) to the private branch exchange (PBX). A business telephone syst ...

(PBX) and other

key telephone system A business telephone system is a multiline telephone system typically used in business environments, encompassing systems ranging in technology from the key telephone system (KTS) to the private branch exchange (PBX). A business telephone syst ...

RJ45S

The RJ45S, a standard jack once specified for modem or data interfaces, uses a mechanically-keyed variation of the 8P8C body with an extra tab that prevents it from mating with other connectors; the visual difference from the more-common 8P8C is subtle. The original RJ45S keyed 8P2C modular connector had pins 5 and 4 wired for tip and ring of a single telephone line, and pins 7 and 8 shorting a programming resistor, but is obsolete today.

RJ48

RJ48 is a registered jack. It is used for T1 and

ISDN Integrated Services Digital Network (ISDN) is a set of communication standards for simultaneous digital transmission of voice, video, data, and other network services over the digitalised circuits of the public switched telephone network. Wo ...

termination and local area data channels or subrate digital services. It uses the eight-position

(8P8C). RJ48C is commonly used for T1 circuits and uses pin numbers 1, 2, 4 and 5. RJ48X is a variation of RJ48C that contains shorting blocks in the jack so that a loopback is created for troubleshooting when unplugged by connecting pins 1 and 4, and 2 and 5. Sometimes this is referred to as a ''self-looping jack''. RJ48S is typically used for local area data channels and subrate digital services, and carries one or two lines. It uses a keyed variety of the 8P8C modular connector. RJ48 connectors are fastened to shielded twisted pair (STP) cables, not the standard unshielded twisted pair (UTP) CAT-(1–5).

RJ61

RJ61 is a physical interface often used for terminating

twisted pair Twisted pair cabling is a type of wiring used for communications in which two conductors of a single circuit are twisted together for the purposes of improving electromagnetic compatibility. Compared to a single conductor or an untwisted ba ...

type cables. It uses an eight position, eight conductor (8P8C)

. This pinout is for multi-line telephone use only; RJ61 is unsuitable for use with high-speed data, because the pins for pairs 3 and 4 are too widely spaced for high signaling frequencies.

T1 line Digital Signal 1 (DS1, sometimes DS-1) is a T-carrier signaling scheme devised by Bell Labs. DS1 is the primary digital telephone standard used in the United States, Canada and Japan and is able to transmit up to 24 multiplexed voice and data cal ...

s use another wiring for the same connector, designated RJ48.

(

10BASE-T 1 (one, unit, unity) is a number representing a single or the only entity. 1 is also a numerical digit and represents a single unit of counting or measurement. For example, a line segment of ''unit length'' is a line segment of length 1. I ...

100BASE-TX In computer networking, Fast Ethernet physical layers carry traffic at the nominal rate of 100 Mbit/s. The prior Ethernet speed was 10 Mbit/s. Of the Fast Ethernet physical layers, 100BASE-TX is by far the most common. Fast Ethern ...

and

1000BASE-T In computer networking, Gigabit Ethernet (GbE or 1 GigE) is the term applied to transmitting Ethernet frames at a rate of a gigabit per second. The most popular variant, 1000BASE-T, is defined by the IEEE 802.3ab standard. It came into use i ...

) also use a different wiring for the same connector, either

T568A ANSI/TIA-568 is a technical standard for commercial building cabling for telecommunications products and services. The title of the standard is ''Commercial Building Telecommunications Cabling Standard'' and is published by the Telecommunications I ...

T568B ANSI/TIA-568 is a technical standard for commercial building cabling for telecommunications products and services. The title of the standard is ''Commercial Building Telecommunications Cabling Standard'' and is published by the Telecommunications I ...

. RJ48, T568A, and T568B are all designed to keep pins close together for pairs 3 and 4. The flat eight-conductor silver-satin cable traditionally used with four-line analog telephones and RJ61 jacks is also unsuitable for use with high-speed data. Twisted pair cabling is required for data applications. Twisted-pair data patch cable used with the three data standards is not a direct replacement for RJ61 cable, because RJ61 pairs 3 and 4 would be split among different patch cable twisted pairs, causing cross-talk between voice lines 3 and 4 that might be noticeable for long patch cables. With the advent of structured wiring systems and TIA/EIA-568 (now ANSI/TIA-568) conventions, the RJ61 pinout is falling into disuse. The T568A and T568B standards are used in place of RJ61 so that a single wiring standard in a facility can be used for both voice and data.

Similar jacks and unofficial names

The following ''RJ''-style names do not refer to official ACTA types. The labels ''RJ9'', ''RJ10'', ''RJ22'' are variously used for

4P4C A modular connector is a type of electrical connector for cords and cables of electronic devices and appliances, such as in computer networking, telecommunication equipment, and audio headsets. Modular connectors were originally developed for ...

and 4P2C modular connectors, most typically installed on telephone handsets and their cordage. Telephone handsets do not connect directly to the public network, and therefore have no registered jack designation. ''RJ45'' is often incorrectly used when referring to an

8P8C A modular connector is a type of electrical connector for cords and cables of electronic devices and appliances, such as in computer networking, telecommunication equipment, and audio headsets. Modular connectors were originally developed for ...

connector used for ANSI/TIA-568 T568A and T568B and

Ethernet Ethernet () is a family of wired computer networking technologies commonly used in local area networks (LAN), metropolitan area networks (MAN) and wide area networks (WAN). It was commercially introduced in 1980 and first standardized in 198 ...

. It is distinct from the official RJ45S and

ARJ45 GG45 (GigaGate 45) and ARJ45 (Augmented RJ45) are two related connectors for Category 7, Category 7A, and Category 8 telecommunication cabling. The GG45 interface and related implementations are developed and sold by Nexans S.A., while the ...

interfaces. ''RJ50'' is often a

10P10C A modular connector is a type of electrical connector for cords and cables of electronic devices and appliances, such as in computer networking, telecommunication equipment, and audio headsets. Modular connectors were originally developed for ...

interface, often used for data applications. The micro ribbon connector, first made by Amphenol, that is used in the RJ21 interface, has also been used to connect Ethernet ports in bulk from a switch with 50-pin ports to a

Cat-5 Category 5 cable (Cat 5) is a twisted pair cable for computer networks. Since 2001, the variant commonly in use is the Category 5e specification (Cat 5e). The cable standard provides performance of up to 100 MHz and is ...

rated

patch panel A patch panel is a device or unit featuring a number of jacks, usually of the same or similar type, for the use of connecting and routing circuits for monitoring, interconnecting, and testing circuits in a convenient, flexible manner. Patch ...

, or between two patch panels. A cable with a 50-pin connector on one end can support six fully wired 8P8C connectors or Ethernet ports on a patch panel with one spare pair. Alternatively, only the necessary pairs for 10/100 Ethernet can be wired allowing twelve Ethernet ports with a single spare pair. This connector is also used with spring bail locks for

SCSI-1 Parallel SCSI (formally, SCSI Parallel Interface, or SPI) is the earliest of the interface implementations in the SCSI family. SPI is a parallel bus; there is one set of electrical connections stretching from one end of the SCSI bus to the oth ...

connections. Some

computer printers In computing, a printer is a peripheral machine which makes a persistent representation of graphics or text, usually on paper. While most output is human-readable, bar code printers are an example of an expanded use for printers. Diffe ...

use a shorter 36-pin version known as a

Centronics connector IEEE 1284 is a standard that defines bi-directional parallel communications between computers and other devices. It was originally developed in the 1970s by Centronics, and was widely known as the Centronics port, both before and after its Insti ...

. The 8P8C modular jack was chosen as a candidate for

systems. In order to be considered, the connector system had to be defined by an international standard, leading to the creation of the ISO 8877 standard. Under the rules of the

IEEE 802 IEEE 802 is a family of Institute of Electrical and Electronics Engineers (IEEE) standards for local area networks (LAN), personal area network (PAN), and metropolitan area networks (MAN). The IEEE 802 LAN/MAN Standards Committee (LMSC) maintains ...

standards project, international standards are to be preferred over national standards, so when the original

twisted-pair wiring version of Ethernet was developed, this modular connector was chosen as the basis for IEEE 802.3i-1990.

References

External links

RJ glossary

ANSI/TIA-968-B
documents o

specifications from th
Administrative Council for Terminal Attachments
section 6.2 in particular
ANSI/TIA-1096-A

Administrative Council for Terminal Attachments

Doing your own telephone wiring

{{DEFAULTSORT:Registered Jack Telephone connectors Computer connectors Networking hardware