RJ45

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Image:Cat5-cable-with-RJ45.jpg Image:Uncrimped rj-45 connector close-up.jpg

RJ45 (Registered Jack 45) is a physical interface often used for terminating twisted pair type cables. "RJ" stands for Registered Jack which is part of the United States Code of Federal Regulations. It has eight "pins" or electrical connections per connector.

1 Wiring
2 Applications
3 See also
4 Notes
5 External links

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Wiring

It is frequently terminated using the T568A or T568B pin/pair assignments that are defined in TIA/EIA-568-B:

RJ45 Wiring (EIA/TIA-568B T568A/T568B)
Pin	T568A Pair	T568B Pair	Wire	T568A Color	T568B Color	Pins on plug (jack is reversed)
1	3	2	tip	Image:Wire white green stripe.svg white/green stripe	Image:Wire white orange stripe.svg white/orange stripe	Image:Pins-RJ-45.png
2	3	2	ring	Image:Wire green.svg green solid	Image:Wire orange.svg orange solid
3	2	3	tip	Image:Wire white orange stripe.svg white/orange stripe	Image:Wire white green stripe.svg white/green stripe
4	1	1	ring	Image:Wire blue.svg blue solid	Image:Wire blue.svg blue solid
5	1	1	tip	Image:Wire white blue stripe.svg white/blue stripe	Image:Wire white blue stripe.svg white/blue stripe
6	2	3	ring	Image:Wire orange.svg orange solid	Image:Wire green.svg green solid
7	4	4	tip	Image:Wire white brown stripe.svg white/brown stripe	Image:Wire white brown stripe.svg white/brown stripe
8	4	4	ring	Image:Wire brown.svg brown solid	Image:Wire brown.svg brown solid

The original concept (RJ11, RJ14, RJ25, RJ48, RJ61) was that the central 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 optimized by alternating the "live" and "earthy" pins of each pair. This pattern for the eight-pin connector results in a pinout where the outermost pair are then too far apart to meet the electrical requirements of high-speed LAN protocols. Two commonly used standard pinouts defined in TIA/EIA-568-B (T568A and T568B) overcome this by using adjacent pairs on the outer four pins. T568A and T568B differ by swapping the locations of the green and orange pairs, and thus have identical performance characteristics. A given location will generally standardize on one of the two options for consistency.

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Applications

A very common application is its use in Ethernet cables, where usually 8 pins (4 pairs) are used, e.g., a male-to-male cable to connect a cable or ADSL modem to the computer Ethernet network card.

Other applications include other networking services such as ISDN and T1.

RJ45 is also used for RS-232 serial interface according to the EIA/TIA-561 standard[1] [2]. The pinout is described there.

See RJXX for other, similar looking jacks, with which the RJ45 is likely (and often) confused.

In floodwired Template:Fn environments the center (blue) pair is often used to carry telephony signals. Where so wired, the physical layout of the RJ45 jack allows for the insertion of an RJ11 in the center of the socket, provided the RJ11 jack is wired to U.S. telephony standards using the center pair. The formal approach to connect telephony equipment is the insertion of a type-approved converter.

The remaining (brown) pair is increasingly used for Power over Ethernet (POE). Legacy equipment may conflict with this use as manufacturers used to short circuit unused pairs to reduce signal cross talk. Some routers/bridges/switches can be powered by the unused 4 lines — blues(+) and browns(-) — to carry current to the unit.

Beware: Different manufacturers of RJ45 jacks arrange for the pins of the RJ45 socket to be linked to wire connectors (often IDC type terminals) that are in a different physical arrangement from that of other manufacturers: Thus, for example, if you are in the habit of connecting your white/orange wire to the "bottom right hand" IDC terminal, which links it to RJ45 pin 1, be aware that on jacks made by other manufacturers this terminal connects instead to RJ45 pin 2, etc!!

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