RJ-45 (Registered Jack - Type 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.
It is usually used with standards like TIA-568B which define the wiring pinout:
RJ-45 Wiring (EIA/TIA-568B)
| Pin | Pair | Wire | Color
|
| 1 | 2 | 1
| white/orange
|
| 2 | 2 | 2
| orange
|
| 3 | 3 | 1
| white/green
|
| 4 | 1 | 2
| blue
|
| 5 | 1 | 1
| white/blue
|
| 6 | 3 | 2
| green
|
| 7 | 4 | 1
| white/brown
|
| 8 | 4 | 2
| brown
|
The original concept (RJ-11, RJ-14, RJ-25, RJ-48 , RJ-61) 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 optimised 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 known as TIA-568A and TIA-568B overcome this by using adjacent pairs on the outer four pins. TIA-568A and TIA-568B differ by swapping the locations of the green and orange pairs, and thus have identical perfomance characteristics. A given location will generally standardize on one of the two options for consistency. (See: Category 5 cable.)
It is normally utilized in telephone sets, with 4 pins (2 pairs).
A very common application is its use in Ethernet cables, where usually 8 pins (4 pairs) are used (i.e. 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.
See RJ-XX for other, similar looking jacks, with which the RJ-45 is likely (and often) confused.
See also