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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 ''Universal Service Ordering Code'' (USOC) 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 (FCC) in the 1970s.〔AT&T, ''Registration Interface—Selection and General Information, Bell System Practices, Section 463-400-100 Issue 1, May 1976〕 They were subsequently codified in the Code of Federal Regulations Part 68.〔〔〔 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. Additionally, 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 world-wide. Specifically, for example, the IEEE 802 standards project has adopted RJ-type interfaces for ISDN (RJ48) and computer networking specifications (RJ45), such as Ethernet. The connectors used for registered jack installations are primarily the modular connector and the 50-pin miniature ribbon connector types. For example, RJ11 uses a six-position two-conductor connector (6P2C), RJ14 uses a six-position four-conductor (6P4C) modular jack, while RJ21 uses a 25-pair (50-pin) 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 (modular 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 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. 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. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Registered jack」の詳細全文を読む スポンサード リンク
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