RJ45
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RJ45 (Registered Jack 45) is a physical interface often used for terminating twisted pair type cables. "RJ" indicates it is part of the Registered Jack family of telecommunications interface standards. It has eight "pins" or electrical connections per connector.
Wiring
It is frequently terminated using the T568A or T568B pin/pair assignments that are defined in TIA/EIA-568-B:
| Pin | T568A Pair | T568B Pair | Wire | T568A Color | T568B Color | Pins on plug (jack is reversed) |
|---|---|---|---|---|---|---|
| 1 | 3 | 2 | tip |
white/green stripe |
white/orange stripe | 
|
| 2 | 3 | 2 | ring |
green solid |
orange solid | |
| 3 | 2 | 3 | tip |
white/orange stripe |
white/green stripe | |
| 4 | 1 | 1 | ring |
blue solid |
blue solid | |
| 5 | 1 | 1 | tip |
white/blue stripe |
white/blue stripe | |
| 6 | 2 | 3 | ring |
orange solid |
green solid | |
| 7 | 4 | 4 | tip |
white/brown stripe |
white/brown stripe | |
| 8 | 4 | 4 | ring |
brown solid |
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 color schemes. T568A is required for US Government installations and recommended for new residential and commercial installations. T568A also has the advantage of being compatible with RJ14. However, T568B is common in commercial installations and continues to be used at those locations for consistency.
Cables that are wired as T568A at one end and T568B at the other are known as "crossover" cables. Such cables often have orange sheaths and, before the widespread acceptance of auto-MDI/MDIX capabilities, were needed to connect hubs to routers.
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[link]. The DE-9<->RJ45 pinout is described here [link].
See Registered jack for other, similar looking jacks, with which the RJ45 is likely (and often) confused.
In floodwired 1 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 crosstalk. 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 may instead connect to RJ45 pin 2 (or any other pin, for that matter).
See also
Notes
Note 1: floodwire is a chiefly British term for installing communications cables in a massive fashion in anticipation of their eventual use.External links
- [How to wire a 10BaseT or 100BaseT connector with Category 5 cable and RJ45 connectors]
- [How to create your own Ethernet Cables]
- [Devices that use RJ45]
- [RJ45 pinout]
- [Catalog page showing the difference between solid and stranded contacts]
| USOC registered jacks RJ9 | RJ11 | RJ12 | RJ14 | RJ21 | RJ25 | RJ45 | RJ48 | RJ50 | RJ61 |
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