Registered jack

This article is about the registered jack (RJ) wiring standard. For other uses of modular connectors, see Modular connector.

Left to right, RJ connectors:

• an eight-contact 8P8C plug (used for RJ49, RJ61 and others, but often called "RJ45" because of its outward resemblance to the true RJ45)
• six-contact RJ25 plug
• four-contact RJ14 plug (often also used instead of two-pin RJ11)
• a four-contact handset plug (also popularly, though incorrectly, called "RJ22", "RJ10", or "RJ9")

RJ25 and RJ14 can be plugged into the same standard six-pin jack, pictured.

A registered jack (RJ) is a standardized physical network interface — both jack construction and wiring pattern — for connecting telecommunications or data equipment to a service provided by a local exchange carrier or long distance carrier. The standard designs for these connectors and their wiring are named RJ11, RJ14, RJ21, RJ48, etc. Many of these interface standards are commonly used in North America, though some interfaces are used world-wide.

The physical connectors that registered jacks use are mainly of the modular connector and 50-pin miniature ribbon connector types. For example, RJ11 uses a 6 position 2 conductor (6P2C) modular plug and jack, while RJ21 uses a 50-pin miniature ribbon connector.

Naming confusion

Strictly, registered jack refers to both the female physical connector (modular connector) and its wiring, but the term is often used loosely to refer to modular connectors regardless of wiring or sex, such as in Ethernet over twisted pair. The RJ designation describes a wiring pattern and not the physical geometry of the connectors.

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 wiring of the 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. 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 with more pins, but if more pins are actually wired, the interface is no longer an RJ11.)

Registered jacks were created by the FCC to be the standard interface between a telephone company and a customer. The wired communications provider (telephone company) is responsible for delivery of services to a minimum point of entry (MPOE) (physically a utility box) which connects the telephone/network wiring on the customers property (customer-premises equipment/CPE) to the communication provider's network. The customer is responsible for jacks, wiring, and equipment on their side of the MPOE. The intent is to establish a universal standard for wiring and interfaces, and to separate ownership of in-home (or in-office) telephone wiring away from (North America's) Bell Systems and relinquish ownership of wiring in an entity's owned structure to that entity.

The various interfaces created due to this regulation were numbered and integrated into the telecommunications' order system by adopting them as Universal Service Order Codes (USOC). USOCs are commonly passed to the communications provider by large businesses for a variety of services. Because there are many standardized interface options available to the customer, the customer must specify the type of interface required, by RJ/USOC. And for a multi-line interface such as the RJ21, they must denote which position(s) of the interface are to be used. If there are multiple RJ21 connectors, they are numbered sequentially and the customer must advise the communications provider of which one to use.

Twisted pair

See also: Category 5 cable and TIA/EIA-568-B

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. 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. For T568A, the inner four pins are wired identically to those in RJ14. In the T568B variant, different pairs are assigned to different pins, so a T568B jack is incompatible with the wiring pattern of RJ14. In connecting cables, however, the performance differences between the pairs that are assigned to different pins are minimal, and in general use T568A and T568B patch cables are interchangeable.

History and authority

Further information: Interconnection

Under the Bell System monopoly (following the Communications Act of 1934), the Bell System owned the phones and did not allow interconnection of separate phones or other terminal equipment. Phones were generally hardwired, or at times used proprietary Bell System connectors.

This began to change with the case Hush-A-Phone v. United States [1956] and the FCC's Carterfone [1968] decision, which required Bell to allow some interconnection, which culminated in registered jacks.

Registered jacks were introduced by the Bell System in the 1970s under a 1976 FCC order ending the use of protective couplers. They replaced earlier, bulkier connectors. The Bell System issued specifications for the modular connectors and their wiring as Universal Service Order 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, Title 47 CFR Part 68, Subpart F superceded by T1.TR5-1999.

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 Attachments (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, "Network and Customer Installation Interface Connector Wiring Configuration Catalog", by reference to specify the wiring. With the publication of TIA-968-B, the connector descriptions have been moved to TIA-1096-A. 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 802.3i-1990, the original 10BASE-T twisted-pair wiring version of Ethernet.

Registered jack types

Common types

6P4C crimp-on style connector commonly used for RJ11 and RJ14

The most familiar registered jack is probably the RJ11. This is a modular connector wired for one plain old telephone service line (using two wires out of six available positions), and is found in most homes and offices in most countries of the world for single-line telephones. Essentially all one, two, and three line analog telephones made today (2009) are meant to plug into RJ11, RJ14, or RJ25 jacks, respectively.

RJ14 is similar, but for two lines, and RJ25 is for three lines. RJ61 is a similar registered jack for four lines. The telephone line cord and its plug are more often a true RJ11 with only two conductors.

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.

List of official registered jacks

Code	Connector	Usage
RJ2MB	50-pin miniature ribbon	2–12 telephone lines with make-busy arrangement
RJ11C/RJ11W	6P2C	For one telephone line (6P4C with power on second pair)
RJ12C/RJ12W	6P6C	For one telephone line ahead of the key system
RJ13C/RJ13W	6P4C	For one telephone line behind the key system
RJ14C/RJ14W	6P4C	For two telephone lines (6P6C with power on third pair)
RJ15C	3-pin weatherproof	For one telephone line
RJ18C/RJ18W	6P6C	For one telephone line with make-busy arrangement
RJ21X	50-pin miniature ribbon	For up to 25 lines
RJ25C/RJ25W	6P6C	For three telephone lines
RJ26X	50-pin miniature ribbon	For multiple data lines, universal
RJ27X	50-pin miniature ribbon	For multiple data lines, programmed
RJ31X	8P8C	Often incorrectly stated as allowing alarm (fire and intrusion) equipment to seize a phone line, the jack is actually used to disconnect the equipment from the phone line while allowing the phone circuit to continue to the site phones. (Only 4C are actually used)
RJ38X	8P8C	Similar to RJ31X, with continuity circuit
RJ41S	8P8C, keyed	For one data line, universal
RJ45S	8P2C, keyed	For one data line with programming resistor
RJ48C	8P8C	For four-wire data line (DSX-1)
RJ48S	8P8C	For four-wire data line (DDS)
RJ48X	8P8C with shorting bar	For four-wire data line (DS1)
RJ49C	8P8C	For ISDN BRI via NT1
RJ61X	8P8C	For four telephone lines
RJ71C	50-pin miniature ribbon	12 line series connection using 50 pin connector (with bridging adapter) ahead of customer equipment. Mostly used for call sequencer equipment.

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 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 doesn't look as nice as a cord plugged into an RJ11C.)

Unofficial plug names

These RJ names do not refer to official ACTA RJ types:

• RJ9, RJ10, RJ22: 4P4C or 4P2C, for telephone handsets. Since telephone handsets do not connect directly to the public network, they have no registered jack code whatsoever.
• RJ45: 8P8C, informal designation for T568A/T568B, including Ethernet; not the same as the true RJ45/RJ45S
• RJ50: 10P10C, often used for data

RJ11, RJ14, RJ25 wiring details

6P6C connector showing the location of pin 1

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 (two, four and six respectively) allowing connections for 1, 2 or 3 phone lines respectively.

Cables sold as RJ11 are nearly always 6P4C (six position, four conductor), with four wires running to a central junction box. Two of its six possible contact positions connect tip and ring and the other two conductors are then unused or used for a second phone line. 6P2C and 6P6C can also be found in stores.

The conductors other than the two central tip and ring conductors are in practice used for various things such as a second or third phone line, a ground for selective ringers, low voltage power for a dial light, or for 'anti-tinkle' circuitry to prevent pulse dialing phones from ringing the bell on other extensions. With tone dialing anti-tinkle measures are not required.

Pinouts

Holding the connector in your hand tab side down with the cable opening toward you, the pins are numbered 1–6, left to right.

Position	Pair	T/R	±	RJ11	RJ14	RJ25	Twisted pair colors	25-pair colors	Old colors[a]	German colors[b]	Australian colors
1	3	T	+			T3	white/green	white/green	white	pink	orange
2	2	T	+		T2	T2	white/orange	white/orange	black	green	red
3	1	R	-	R1	R1	R1	blue	blue/white	red	white	blue
4	1	T	+	T1	T1	T1	white/blue	white/blue	green	brown	white
5	2	R	-		R2	R2	orange	orange/white	yellow	yellow	black
6	3	R	-			R3	green	green/white	blue	gray	green

• ^[a] While the old solid color code was well established for pair 1 and usually pair 2, there are several conflicting conventions for pair 3 (and sometimes even pair 2). The colors shown above were taken from a vendor of "silver satin" flat 8-conductor phone cable that claims to be standard. 6-pair solid (old) bellwire cables previously used by the Bell System use white for pair 3 tip but some vendor's cable may substitute orange for white. At least one other vendor of flat 8-conductor cable uses the sequence blue, orange, black, red, green, yellow, brown and white/slate.
• ^[b] This color scheme originates in the (withdrawn) national standard DIN 47100. The scheme shown here is the correct color code for interfacing with the RJ connector standards.

  However, with German domestic telephone equipment (and that in some neighbouring countries), 6P4C plugs and sockets are typically only used to connect the telephone cable to the phone base unit, whereas the mechanically different TAE plug is used at the other end of the cable. Older base units may accommodate the additional connectors of TAE (E, W, a2, b2) and may feature non-RJ standard sockets that can be connected „straight“ to TAE plugs. Further, flat DIN 47100 cables typically place the wires in ascending order. When used directly with 6P4C plugs, the colors will be garbled.

Powered version of RJ11

In the powered version, Pins 2 and 5 (black and yellow) may carry low voltage AC or DC power. While the phone line itself (tip and ring) supplies enough power for most telephone terminals, old telephone terminals with incandescent lights in them (such as the classic Western Electric Princess and Trimline telephones) need more power than the phone line can supply. Typically, the power on Pins 2 and 5 comes from a transformer plugged into a wall near one jack, supplying power to all of the jacks in the house. Trimline and Princess phone dial lights are rated at 6.3 volts and the transformer output is typically around 5 volts, providing a long service life for the incandescent lamps.

Compatibility with structured cabling

With the rise of Ethernet local area networks operating over Cat5e and Cat6 unshielded twisted pair cable, structured cabling networks adhering to TIA/EIA-568-B are widely used for both computer networking and analog telephony. The 8P8C (RJ45) jack used by TIA/EIA-568-B physically accepts the 6-position connector used by RJ11, RJ14 and RJ25, but only RJ11 and RJ14 have full electrical compatibility. TIA/EIA-568-B splits the third pair of RJ25 across two separate cable pairs, rendering it unusable. This was necessary to preserve the electrical properties of those pairs for Ethernet, which operates at much higher frequencies than analog telephony.

Both the third and fourth pairs of RJ61 are similarly split. Because of this incompatibility, and because they were never very common to begin with, the TIA/EIA-568-B conventions are displacing RJ25 and RJ61 for telephones with more than two lines.

RJ21

Female RJ21 connector

RJ21 is a registered jack standard for a modular connector using 50 conductors, usually used to implement a 25-line (or less) telephone connection such as that used in the 1A2 key telephone system. It is also known as a 50-pin telco connector, CHAMP(AMP) or an Amphenol connector. (The latter is a genericized trademark, as Amphenol was the largest manufacturer of these at one time.)

Dual RJ21 connectors are often used on punch blocks to make a breakout box for PBX and other key telephone systems.

RJ21 connectors are used to connect Ethernet ports in bulk from a switch with RJ21 ports to a CAT-5 rated patch panel, or between two patch panels. A cable with an RJ21 connector on one end can support 12 8P8C "RJ45" connectors or Ethernet ports on a patch panel.

The same connector (with spring bail locks) is used for SCSI-1 connections. Some computer printers use a shorter 36-pin version known as a Centronics connector.

A cable color scheme, in common use, is determined for 25 pairs of conductors as follows. For each tip, the primary, more prominent color is chosen from {blue, orange, green, brown, slate}, in that order, and the secondary, thinner stripe color from {white, red, black, yellow, violet}, in that order. The ring conductor color scheme uses the same colors as the matching tip 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 x 5 + 2 - 5 = 17th pair of wires. If the yellow is the more prominent, thicker stripe, then the wire is a ring conductor connecting to the pin numbered 25 + the pair #, which is pin 42 in this case. (Tip conductors connect to the same pin number as the pair number.)

A conventional enumeration of wire color pairs then begins blue (& white), orange (& white), green (& white) and brown (& white), which subsumes a color coding convention used in cables of 4 or fewer pairs (8 wires or less) with 8P and 6P connectors.

Color	Pin (Tip)		Pin (Ring)	Color
White/Blue	26		1	Blue/White
White/Orange	27		2	Orange/White
White/Green	28		3	Green/White
White/Brown	29		4	Brown/White
White/Slate	30		5	Slate/White
Red/Blue	31		6	Blue/Red
Red/Orange	32		7	Orange/Red
Red/Green	33		8	Green/Red
Red/Brown	34		9	Brown/Red
Red/Slate	35		10	Slate/Red
Black/Blue	36		11	Blue/Black
Black/Orange	37		12	Orange/Black
Black/Green	38		13	Green/Black
Black/Brown	39		14	Brown/Black
Black/Slate	40		15	Slate/Black
Yellow/Blue	41		16	Blue/Yellow
Yellow/Orange	42		17	Orange/Yellow
Yellow/Green	43		18	Green/Yellow
Yellow/Brown	44		19	Brown/Yellow
Yellow/Slate	45		20	Slate/Yellow
Violet/Blue	46		21	Blue/Violet
Violet/Orange	47		22	Orange/Violet
Violet/Green	48		23	Green/Violet
Violet/Brown	49		24	Brown/Violet
Violet/Slate	50		25	Slate/Violet

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 8 position modular connector.

RJ48C is commonly used for T1 lines and uses pins 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 "smart jack".

RJ48S is typically used for local area data channels/subrate digital services, and carries one or two lines. It uses a keyed variety of the 8P8C modular connector.

RJ48 connectors are fastened to STP (Shielded Twisted Pair) cables, not the standard UTP (Unshielded Twisted Pair) CAT-(1-5).

RJ48C and RJ48X wiring

Pin	Pair	Signal	Color
1	R	RX Ring	Orange/White
2	T	RX Tip	White/Orange
3		reserved	White/Green
4	R1	TX Ring	Blue/White
5	T1	TX Tip	White/Blue
6		reserved	Green/White
7		shield	White/Brown
8		shield	Brown/White

Crossover Wiring

Router to Router (RJ48C) Crossover, uses an 8 position connector and UTP (Unshielded Twisted Pair) cable. TIA/EIA-568#Wiring defines a telecommunications standard for enumerating all 4 wire pairs that is more comprehensive than what is needed for 10/100Base-T (see 10Base-T / 100Base-T) Ethernet cables, which only require 2 twisted pair conductors on pins 1,2,3 and 6. These 10/100 Base-T Ethernet specific cables often use only blue and orange colored wires to enumerate wire pairs 1 and 2. To confuse the issue, this convention is sometimes applied to fully populated connectors so that the central pin contacts are no longer the blue pair (but green), emphasizing the cables colour coding for data and not as TIA/EIA-568 for voice communications! Electrically, however, the colors make no difference as long as correct pin to pin wire pairings are made, where, fortunately the TIA/EIA-568 conventions subsume those needed for Ethernet.

Pin	Pin	Color
1	3	White/Orange
2	6	Orange/White
3	1	White/Green
4	4	Blue/White
5	5	White/Blue
6	2	Green/White
7	7	White/Brown
8	8	Brown/White

Note that the following table is identical to the above but rearranged numerically by the second connector pinout. This identifies a conventional numbering of a wire pair and the pins on the second connector associated with each pair. 10BASE-T and 100BASE-TX Ethernet signaling only requires the two wire pairs occupying pins 1, 2, 3 and 6, thus the orange pair and green pair (pairs 2 and 3 in this table) effect the crossover, however 1000BASE-T requires all four pairs to operate.

Pin	Pin	Pair	Color
3	1	3	White/Green
6	2	3	Green/White
1	3	2	White/Orange
4	4	1	Blue/White
5	5	1	White/Blue
2	6	2	Orange/White
7	7	4	White/Brown
8	8	4	Brown/White

Naming confusion

People sometimes refer to the 10P10C modular connector as RJ48. The origin of this misnomer is unknown; none of the RJ48 registered jacks uses a 10P10C connector. However, it may be an outgrowth of the common misperception of the RJ USOCs as names of physical connectors. If one knew of the names RJ45 and RJ48 and knew of the 8P8C and 10P10C modular connectors, and believed (as explained in the RJ45 article) that RJ45 is the name of the 8P8C, one might conclude that RJ48 is the name of the larger 10P10C.

RJ61

Not to be confused with RJ45.

See also: 8P8C and Ethernet over twisted pair

RJ61 is a physical interface often used for terminating twisted pair type cables. It is one of the Registered Jacks, and uses an eight position, eight conductor (8P8C) modular connector.

RJ61 specifies the wiring pinout of the connector as follows:

RJ61 wiring (USOC)

Pin	Pair	Wire	Color
1	4	tip	White/Brown
2	3	tip	White/Green
3	2	tip	White/Orange
4	1	ring	Blue/White
5	1	tip	White/Blue
6	2	ring	Orange/White
7	3	ring	Green/White
8	4	ring	Brown/White

This pinout is for multi-line telephone use only; RJ61 is unsuitable for use with Ethernet over twisted pair (10BASE-T, 100BASE-TX and 1000BASE-T) because the pins for pairs 3 and 4 are too widely spaced. This causes excessive crosstalk at the high signaling frequencies used by Ethernet, which uses the pinouts specified in TIA-568A/B instead. The pairings for the middle four pins are the same in all three pinouts, but the pair assignments differ; only pair 1 is the same in all three, and pair 2 is the same only in RJ61 and TIA-568A.

With the advent of structured wiring systems that can be used for either voice or data (Ethernet), the RJ61 pinout is falling into disuse because of its unsuitability for Ethernet. The EIA/TIA-568A/B conventions are instead used for both voice and data.

Note that the flat 8-conductor "silver satin" cable traditionally used with 4-line analog telephones is unsuitable for use with Ethernet, even though both applications use the 8P8C modular connector. Twisted pair cable and the pairings given in TIA-568A/B (which are different from the pairings shown above) must be used with Ethernet. The 8-conductor phone wiring is RJ61. T1 lines use another wiring for the same connector, designated RJ48.

See also

• Telephone plug
• Interconnection
• Modified Modular Jack – A variation used by Digital Equipment Corporation for serial computer connections
• BS 6312 – British equivalent to RJ25
• 4P4C – Handset jack
• 8P8C – Eight position connector used with twisted pair Ethernet as well as RJ45 and RJ61 telephone applications
• Key telephone system
• Telco cable
• Micro ribbon

Further reading

• RJ glossary
• RJ48C, RJ48S, RJ48X
• T1 & T3 RJ48 cables
• Registered Jack reference guide
• TIA-968-A or tia-eia-is-968 documents of FCC specifications from the Administrative Council for Terminal Attachments, section 6.2 in particular
• TIA-1096-A
• UTP cable termination standards 568A vs 568B
• John R. Carlsen: On wiring modular telephone connectors
• Modular jack wiring
• Modular wiring reference showing differences between 8P8C, true RJ45 8-position keyed connector, 6P6C, and 6-position modified offset tab
• Common outlet configurations graphical representation of twisted pair pinouts

External links

• Administrative Council for Terminal Attachments
• Doing your own telephone wiring
• Connecting a second phone line