Registered jack


A registered jack 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 Universal Service Ordering Code system of the Bell System in the United States for complying with the registration program for customer-supplied telephone equipment mandated by the Federal Communications Commission in the 1970s. They were subsequently codified in title 47 of the Code of Federal Regulations Part 68. Registered Jack connections began to see use after their invention in 1973 by Bell Labs.
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 and the 50-pin miniature ribbon connector. For example, RJ11 uses a six-position two-conductor connector, RJ14 uses a six-position four-conductor modular jack, while RJ21 uses a 25-pair miniature ribbon connector.

Naming standard

The registered jack designations originated in the standardization processes in the Bell System in the United States, and describe application circuits and not just the physical geometry of the connectors; inspection of the connector does not necessarily show which registered jack wiring is used. The same modular connector type may be used for different registered jack applications.
Strictly, Registered Jack refers to both the female physical connector and its wiring, but the term is often used loosely to refer to modular connectors regardless of wiring or gender, such as in Ethernet over twisted pair. There is much confusion over these connection standards. The same six-position plug and jack commonly used for telephone line connections may be used for RJ11, RJ14 or even RJ25, all of which are names of interface standards that use this physical connector. The RJ11 standard dictates a single wire pair connection, while RJ14 is a configuration for two lines, and RJ25 uses all six wires for three telephones lines. The RJ designations, though, only pertain to the wiring of the jack, hence the name Registered Jack; it is commonplace, but not strictly correct, to refer to an unwired plug by any of these names.
Modular connectors were developed to replace older telephone installation methods that used either hardwired cords, or bulkier varieties of telephone plugs. The common nomenclature for modular connectors includes the number of contact positions and the number of wires connected, for example 6P indicates a six-position modular plug or jack. A six-position modular plug with conductors in the middle two positions and the other four positions unused has the designation 6P2C. RJ11 uses a 6P2C connector. The connectors could be supplied with more pins, but if more pins are actually wired, the interface is not an RJ11.

History and authority

Registration interfaces were created by the Bell System under a 1976 Federal Communications Commission order for the standard interconnection between telephone company equipment and customer premises equipment. These interfaces used newly standardized jacks and plugs, primarily based on miniature modular connectors.
The wired communications provider is responsible for delivery of services to a minimum point of entry. 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 telephone wiring from the wiring owned by the service provider.
In the Bell System, following the Communications Act of 1934, the telephone companies owned all telecommunications equipment and they did not allow interconnection 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 and the Federal Communications Commission's Carterfone 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, 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 and codified in the Code of Federal Regulations, Title 47 CFR Part 68, Subpart F, 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. 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. ACTA and TIA jointly published the standard TIA/EIA-IS-968, 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", 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 for each application.

Registered jack 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 RJ45 jack is rarely used.
The officially recognized types of registered jacks are listed in the following table:
CodeConnectorUsage
RJA1X225A adapterConnector for a modular plug to a four-prong jack
RJA2X267A adapterConnector for splitting one modular jack to two modular jacks
RJA3X224A adapterConnector for adapting a modular plug to a 12-prong jack
RJ2MB50-pin2–12 telephone lines with make-busy arrangement
RJ116P2CEstablishes a bridged connection for one telephone line
RJ126P6CEstablishes a bridged connection for one telephone line with key telephone system control ahead of line circuit
RJ136P4CSimilar to RJ12, but behind the line circuit
RJ146P4CFor two telephone lines
RJ15C3-pin weatherproofFor one telephone line for boats in marinas
RJ186P6CFor one telephone line with make-busy arrangement
RJ21X50-pinMultiple line bridged T/R configuration
RJ256P6CFor three telephone lines
RJ26X50-pinFor multiple data lines, universal
RJ27X50-pinFor multiple data lines, programmed
RJ31X8P8CAllows an alarm system to seize the telephone line to make an outgoing call during an alarm. Jack is placed closer to the network interface than all other equipment. Only 4 conductors are used.
RJ32X8P8CLike RJ31X, this wiring provides a series tip and ring connection through the connecting block, but is used when the customer premises equipment is connected in series with a single station, such as an automatic dialer.
RJ33X8P8CThis wiring provides a series tip and ring connection of a KTS line ahead of the line circuit because the registered equipment requires CO/PBX ringing and a bridged connection of the A and A1 lead from behind the line circuit. Tip and ring are the only leads opened when the CPE plug is inserted. Typical usage is for customer-provided automatic dialers and call restrictors.
RJ34X8P8CSimilar to RJ33X, but all leads are connected behind the line circuit.
RJ35X8P8CThis arrangement provides a series tip and ring connection to whatever line has been selected in a key telephone set plus a bridged A and A1 lead.
RJ38X8P4CSimilar to RJ31X, with a continuity circuit. If the plug is disconnected from the jack, shorting bars allow the phone circuit to continue to the site phones. Only 4 conductors are used.
RJ41S8P8C, keyedFor one data line, universal
RJ45S8P8C, keyedFor one data line, with programming resistor
RJ48C8P4CFor four-wire data line
RJ48S8P4C, keyedFor four-wire data line
RJ48X8P4C with shorting barFor four-wire data line
RJ49C8P8CFor ISDN BRI via NT1
RJ61X8P8CFor four telephone lines
RJ71C50-pin12 line series connection using 50-pin connector ahead of customer equipment. Mostly used for call sequencer equipment.

Many of the basic names have suffixes that indicate subtypes:
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 positions and the actual number of contacts installed within these positions. RJ11, RJ14, and RJ25 all use the same six-position modular connector, thus are physically identical except for the different number of contacts 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 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 for selective ringers, low-voltage power for a dial light, or for anti-tinkle circuitry to prevent pulse dialing 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:
PositionPairTip or
Ring
±RJ11RJ14RJ25U.S. Bell System colors25-pair color codeGerman colorsAustralian colorsDutch colors
13T+T3 or
white or orange

white/green

violet

orange
Not used
22T+T2T2
black

white/orange

green

red

orange
31RR1R1R1
red

blue/white

white

blue

red
41T+T1T1T1
green

white/blue

brown

white

blue
52RR2R2
yellow

orange/white

yellow

black

white
63RR3 or
blue or brown

green/white

slate

green
Not used

Some telephones such as the Western Electric Princess and Trimline telephone models require additional power for operation of the incandescent dial light. This power is delivered to the telephone set from a transformer by the second wire pair of the 6P4C connector.

RJ21

RJ21 is a registered jack standard using a modular connector with contacts for up to fifty conductors. It is used to implement connections for up to 25 lines, or circuits that require many wire pairs, such as used in the 1A2 key telephone system. The miniature ribbon connector of this interface is also known as a 50-pin telco connector, CHAMP, or Amphenol connector, the latter being a genericized trademark, as Amphenol was a prominent manufacturer of these at one time.
A cable color scheme, known as even-count color code, 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 with a yellow 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, orange, green and brown, which subsumes a color-coding convention used in cables of 4 or fewer pairs with 8P and 6P connectors.
Dual 50-pin ribbon connectors are often used on punch blocks to create a breakout box for private branch exchange and other key telephone systems.

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.
The 8P8C connector is often incorrectly called RJ45 connector in several fields such as telecommunications and computer networking but it lacks the extra tab.

RJ48

RJ48 is a registered jack. It is used for T1 and ISDN termination and local area data channels/subrate digital services. It uses the eight-position modular connector.
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 cables, not the standard unshielded twisted pair CAT-.

RJ61

PinPairSignalColor
14Tip White/brown
23Tip White/green
32Tip White/orange
41Ring Blue/white
51Tip White/blue
62Ring Orange/white
73Ring Green/white
84Ring Brown/white

RJ61 is a physical interface often used for terminating twisted pair type cables. It uses an eight position, eight conductor modular connector.
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 lines use another wiring for the same connector, designated RJ48. Ethernet over twisted pair also use a different wiring for the same connector, either T568A or T568B. 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-B 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 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 used when referring to an 8P8C connector used for T568A/T568B and Ethernet. It is distinct from the official RJ45S interface.
RJ50 is often a 10P10C 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 rated patch panel, or between two patch panels. A cable with a 50-pin connector on one end can support 6 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 connections. Some computer printers use a shorter 36-pin version known as a Centronics connector.
The 8P8C modular jack was chosen as a candidate for ISDN 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 standards project, international standards are to be preferred over national standards, so when the original 10BASE-T twisted-pair wiring version of Ethernet was developed, this modular connector was chosen as the basis for IEEE 802.3i-1990.