Registered jack
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- an eight-contact 8P8C plug (used for RJ49, RJ61 and others, but often called "RJ45" because of its outward semblance 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")
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 4 conductor (6P4C) modular plug and jack, while RJ21 uses a 50-pin miniature ribbon connector.
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[edit] 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, such as in Ethernet over twisted pair.
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 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 customer's property (CPE - Customer-premises equipment) 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.
[edit] 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.
[edit] 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; a popular saying was "Ma Bell has you by the calls". 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, 47 CFR 68, subpart F.
In January 2001, the FCC turned over responsibility for standardizing connections to the telephone network to a new private industry organization, the Administrative Council for Terminal Attachment (ACTA). The FCC removed Subpart F from the CFR and added Subpart G, which delegates the task to the ACTA. The ACTA published a standard called TIA/EIA-IS-968 which contained the information that was formerly in the CFR. The current version of that standard, called TIA-968-A, specifies the modular connectors at length, but not the wiring. Instead, TIA-968-A incorporates a standard called T1.TR5-1999 by reference to specify the wiring. With the publication of ANSI/TIA-968-B, the connector descriptions have been moved to ANSI/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).
[edit] 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.
[edit] Registered jack types
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It has been suggested that RJ11, RJ14, RJ25, RJ21, RJ48 and RJ61 be merged into this article or section. (Discuss) |
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It has been suggested that this section be split into a new article titled List of registered jacks. (Discuss) |
The most familiar registered jack is probably the RJ11. This is a 6 position modular connector wired for one phone line, and is found in most homes and offices in North America for single line telephones.
RJ14 and RJ25 are also fairly common, using the same size connector as RJ11, but with two and three phone lines, respectively, connected.
Essentially all one, two, and three line analog telephones made today (2009) are meant to plug into RJ11, RJ14, or RJ25 jacks, respectively.
The true RJ45(S) is an extremely uncommon registered jack, but the name "RJ45" is also used quite commonly to refer to any 8P8C modular connector.
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.
[edit] "Unofficial" (incorrect) plug names
These "RJ" names do not really refer to truly existing 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
[edit] See also
[edit] External links
- RJ glossary
- TIA-968-A - Contains dimensions for jacks and plugs.
- RJ reference - Descriptions and applications
- Administrative Council for Terminal Attachments
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