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.
Network interface controller, the device a computer uses to connect to a computer network
Local Exchange Carrier (LEC) is a regulatory term in telecommunications for the local telephone company.
"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, such as in Ethernet over twisted pair.
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. 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
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 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,
Title 47 CFR Part 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 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 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.
Common types
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.[1] 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 types
Many of the basic names have suffixes that indicate subtypes:
C: flush-mount or surface mount
W: wall-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.)
RJ2MB: 50-pin miniature ribbon connector, 2-12 telephone lines with make-busy
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 (key telephone system)
RJ13C/RJ13W: 6P4C, for one telephone line behind the key system (key telephone 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 connector, for up to 25 lines
RJ25C/RJ25W: 6P6C, for three telephone lines
RJ26X: 50-pin miniature ribbon connector, for multiple data lines, universal
RJ27X: 50-pin miniature ribbon connector, for multiple data lines, programmed
RJ31X: 8P8C (although usually only 4C are used), 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.
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
RJ48S: 8P8C, for four-wire data line (DDS)
RJ48C: 8P8C, for four-wire data line (DSX-1)
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: 12 line series connection using 50 pin connector (with bridging adapter) ahead of customer equipment.
Mostly used for call sequencer equipment.
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, for data
RJ11, RJ14, RJ25 wiring details
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).
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. 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 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.
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.
Pinouts
RJ14 6P4C crimp-on style connector
Holding the connector in your hand tab side down with the cable opening toward you, the pins are numbered 1-6, left to
right. The multi-conductor cables attached to RJ11 connectors usually have colored sheaths.
RJ25 RJ14 RJ11 Twisted pair Old German Australian
position Pair T/R ± 25-pair colors
pin pin pin colors colors[a] colors[b] Colours
1 1 3 T + white/green white/green white pink orange
2 2 1 2 T + white/orange white/orange black green red
3 3 2 1 1 R – blue blue/white red white blue
4 4 3 2 1 T + white/blue white/blue green brown white
5 5 4 2 R – orange orange/white yellow yellow black
6 6 3 R – green green/white blue gray green
^[a] While the old solid color code was well established for pairs 1 and 2, there are several conflicting conventions for
pair 3. 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.
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.
Modular connector is the name given to a family of electrical connectors examples of which are pictured. These
connectors were originally used in telephone wiring. Even though they are still used for that purpose they are used for a
variety of other things as well. A modular connector's advantage over many other kinds include small size and ease of
plugging and unplugging. However the plastic retaining spring clip tends to get broken off when cables are pulled from
storage for use. If that happens, the plug can easily fall out of the wall jack. Many uses that originally used a bulkier
connector have migrated to modular connectors. Probably the most well known applications of modular connectors is for
telephone jacks and for Ethernet jacks, which are nearly always modular connectors.
An 8P8C modular plug. This is the common crimp type plug, of the same kind pictured above crimped onto a cable (with
moulded sleeve)
Sizes and contacts
Modular connectors have positions, some or all of which have contacts in them, some or all of which have wires
attached; positions with omitted contacts or contacts unattached to wires are unused for the electrical connection, but
ensure that the plug fit correctly. For instance, RJ11 wires usually have connectors with 6 positions and 4 contacts, to
which are attached 2 wires.
Modular connectors come in four sizes: 4-, 6-, 8-, and 10-position, where a position is a location for a contact. Not all of
the positions may have contacts: when contacts are omitted, they are typically done so from the outermost two contacts
inward, such that the number of contacts is always an even number.
The connectors are typically designated using two numbers that represent the quantity of positions and contacts, with each
number followed by a "P" and "C", respectively: for example, "6P2C" for a connector having 6 positions and 2 contacts.
Alternate designations omit the "P" and "C" while separating the position and contact quantities with either an "x" ("6x2")
or a slash ("6/2").
The dimensions of the connectors are such that a plug can be inserted into a jack that has more positions than the plug,
leaving the jack's outermost contacts unterminated. However, not all plugs from all manufacturers have this capability,
and some jack manufacturers warn that their jacks are not designed to accept smaller plugs without damage.
When all of the positions have contacts, the contacts are numbered sequentially starting from 1. When viewed head-on
with the retention mechanism on the bottom, jacks will have contact number 1 on the left and plugs will have it on the
right. If the connector has positions that do not have contacts, the remaining contacts are numbered as if all of the
positions had contacts: for example, on a 6-position, 2-contact plug, where the outermost four positions do not have
contacts, the innermost two contacts are numbered 3 and 4.
Some modular connectors are indexed: their dimensions are intentionally non-standard, preventing connections with
connectors of standard dimensions. The means of indexing may be non-standard cross-section dimensions or shapes,
retention mechanism dimensions, or retention mechanism quantity.
Pinouts
Contact assignments, or pinouts, vary by application. While standardized for telephone applications by registered jack
standard, and Ethernet over twisted pair by the TIA/EIA-568-B standard, there may be no standardization within an
application: for example, there are multiple conventions for use of 8P8C connectors for RS-232.
For this reason, D-sub-to-modular adapters are typically shipped without the D-sub contacts (pins or sockets) terminated,
so that the D-sub-to-modular contact pairing can — and must — be performed by the end-user.
Gender
Modular connectors have gender: male connectors are called plugs, while female connectors are called jacks or,
sometimes, sockets.
The choice of gender is generally based on the location of the connector: plugs are used to terminate loose cables and
cords, while jacks are used for fixed locations on surfaces such as walls and panels. (This is in contrast to some other
connector systems, where the choice of gender is based on the function of the connector: for example, in power cabling
systems, female connectors deliver power, while male connectors receive power.) Cables with a plug on one end and a
jack on the other are rare; instead, cables that have the more common arrangement of plugs on both ends are connected
using a male-to-male adapter, which has two jacks.
Category 5
Category 5 cable is a twisted pair high signal integrity cable type often referred to as Cat5 or Cat-5. Most
Category-5 cables are unshielded, relying on the twisted pair design for noise rejection. Category 5 has been
superseded by the Category 5e specification. This type of cable is used in structured cabling for computer
networks such as Ethernet and ATM, and is also used to carry many other signals such as telephony and video.
Cable standard
The specification for Category 5 cable was defined in ANSI/TIA/EIA-568-A, with clarification in TSB-95.
These documents specified performance characteristics and test requirements for frequencies of up to 100 MHz.
Category 5[2] cable includes twisted pairs in a single cable jacket. This use of balanced lines helps preserve a
high signal-to-noise ratio despite interference from both external sources and other pairs (this latter form of
interference is called crosstalk). It is most commonly used for 100 Mbit/s networks, such as 100BASE-TX
Ethernet, although IEEE 802.3ab defines standards for 1000BASE-T – Gigabit Ethernet over category 5 cable.
Each of the four pairs in a Cat 5 cable has differing precise number of twists per metre based on prime numbers
to minimize crosstalk between the pairs. On average there are 6 twists per 5 centimetres. The pairs are made
from 24 gauge (AWG) copper wires within the cables.
Connectors and other information
The cable exists in both stranded and solid conductor forms. The stranded form is more flexible and withstands
more bending without breaking and is suited for reliable connections with insulation piercing connectors, but
makes unreliable connections in insulation-displacement connectors. The solid form is less expensive and
makes reliable connections into insulation displacement connectors, but makes unreliable connections in
insulation piercing connectors. Taking these things into account, building wiring (for example, the wiring inside
the wall that connects a wall socket to a central patch panel) is solid core, while patch cables (for example, the
movable cable that plugs into the wall socket on one end and a computer on the other) are stranded. Outer
insulation is typically PVC or LSOH.
Cable types, connector types and cabling topologies are defined by TIA/EIA-568-B. Nearly always, 8P8C
modular connectors, often incorrectly referred to as "RJ-45", are used for connecting category 5 cable. The
specific category of cable in use can be identified by the printing on the side of the cable.[3]
The cable is terminated in either the T568A scheme or the T568B scheme. Canada and Australia use the T568A
standard, and the United States commonly uses T568B scheme. It really doesn't make any difference which is
used as long as you use only one of the standards so all connections are the same at your location to avoid
confusion and potential problems. Mixed cable types should not be connected in series as the impedance per
pair differs slightly and may cause signal degradation. The article Ethernet over twisted pair describes how the
cable is used for Ethernet, including special "cross over" cables.
Conductors required
10BASE-T (IEEE) and 100BASE-TX (IEEE) Ethernet connections require two cable pairs. 1000BASE-T
(IEEE) and 1000BASE-TX (TIA/EIA-854, requiring category 6 cabling) Ethernet connections require four
cable pairs. Four pair cable is by far most commonly available type.
Bending radius
Most Cat.5 cables can be bent at a radius approximately 4 times the diameter of the cable.[4]
Characteristics
Electrical characteristics for Cat.5e UTP
Property Nominal Value Tolerance Unit ref
[5]
Characteristic impedance @ 100 MHz 100 ± 15 Ω
[5]
Nominal characteristic impedance @ 100 MHz 100 ±5 Ω
[5]
DC-Loop resistance ≤ 0.188 Ω/m
[5]
Propagation speed 0.64 c
[5]
Propagation delay 4.80-5.30 ns/m
[5]
Delay skew < 100 MHz < 0.20 ns/m
[5]
Capacitance at 800 Hz 52 pF/m
[6]
Inductance 525 nH/m
[6]
Cutoff frequency 50323 Hz
[5]
Max tensile load, during installation 100 N
[5][7]
Wire size AWG-24 (0.205 mm² )
[5]
Insulation thickness 0.245 mm
[7]
Maximum current per conductor 0.577 A
[5]
Temperature operating -55 to +60 °C
Dielectric
Example materials used as dielectric in the cable[8]
Acronym Material
PE Polyethylene
FP Foamed polyethylene
FEP Teflon / Fluorinated Ethylene Propylene
FFEP Foamed Teflon / Fluorinated Ethylene Propylene
AD/PE Air dielectric / Polyethylene
Individual twist lengths
By altering the length of each twist, crosstalk is reduced, without affecting the impedance.[6]
Pair color [cm] per turn Turns per [m]
Green 1.53 65.2
Blue 1.54 64.8
Orange 1.78 56.2
Brown 1.94 51.7