Network, Computer and Programming Resources

Network - RJ-xx

RJ-xx is a modular connection mechanism originally developed by the telephone company. (RJ stands for registered jack.) The connection allows for up to eight wires (used as four pairs). In RJ-xx connections, the jack is the female component and the plug is the male component. Various RJ configurations are available. These are distinguished by the following: n Number of wire pairs used (generally two, three, or four) n Which wire pairs are used (known as the wiring sequence) n Keying or other modifications to the plug and jack, designed to make correct connections easier and incorrect connections less likely For example, the telephone company commonly uses two-pair wire in an unkeyed connection. The first wire pair, which uses the two middle positions, carries the voice signal for the primary line. Strictly speaking, the RJ designation applies only to cable that uses a particular wiring scheme (USOC, as described in the Wiring Sequence article). Other wiring sequences have different designations. However, RJ has become a generic designation to describe any type of modular connection. The following are some commonly used RJ connections: RJ-11: Four-wire (two-pair) connection. The telephone company version is used for ordinary single-line residential and business telephone lines. The two central wires (green and red) are tip and ring lines, respectively. RJ-12: Six-wire (three-pair) connection. RJ-11 and RJ-12 connections use the same-sized plug and jack. RJ-45: Eight-wire (four-pair) connection. The telephone company version is used for connections with multiple lines in the same location. If there is no competition for wires, such a connection can also be used for 10BaseT networks. An RJ-45 connection uses a larger plug and jack than for RJ-11 or RJ-12. For unkeyed connections, you can connect an RJ-11 or RJ-12 plug to an RJ-45 jack, but you cannot fit an RJ-45 plug into an RJ-11/12 jack. Although the "user-ends" of RJ-xx jacks all look alike, there are two ways of attaching this type of connector to the cable itself. One type of connector has prongs that wrap around the wire when the connector is crimped onto the cable. This type is used with solid, or single-strand, wire. The other type has prongs that pierce the wire when the connector is attached, and it is used for multistrand wire.