RJ45: All About the Network Connector


RJ45 is the most common twisted-pair connector for Ethernet cables and networks. RJ means “registered jack”, which 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.

What Is an Ethernet Cable?

Ethernet networks, modem and router wiring typically use the physical connector RJ45. All commercial wiring and telecommunications products under the 3 EIA / TIA-568-B standards have adopted it as a connection. Therefore, it is one of the most popular link connections that exist today, although wireless networks have become popular in homes and offices but are still being used for many applications.

EIA (Electronic Industries Alliance), an association of electronics and technology companies in the United States whose purpose is to develop and promote competitiveness in this industry, was responsible for creating the RJ45 (Registered Jack).

Pinouts of RJ45 Connectors

The RJ45 has a plastic structure, normally transparent (there may be other colors), which contains 8 metal pins for connection. In addition, it has a kind of semi clamp with a tab that fits in the port so that it does not move or release, since it is a connector that will support data transfers, it must be secured.

As for the connection of their cables, they can be done in two ways. One of them is by a crimper stripping the ends of the cables and connecting them manually. Another is through an automated industrial process, which is used for cables produced by manufacturers. However, surely, if you work with this type of network equipment, surely you have ever had to do it manually to create a twisted pair for example

Type of Connections

The cable connections that we have described in the previous section can be made in several possible ways and thus the application for which the RJ45 cable is to be used is varied. The ways to connect them are:

  • >Direct: the same order of pins is respected at both ends, that is, it will connect the same in the two RJ45s that we have in a cable. In this case, devices that are unequal can be connected, for example a PC and a switch, or a PC and a hub, etc.
  • > Crossed: very popular in applications to connect two equal devices in a network to be able to transmit data between them without an intermediate device. For example, you could connect two PCs directly through their network cards with a crossover cable. To do this, the RX and TX cables must be crossed, so that when one PC transmits through the TX it receives the other PC through RX, and vice versa.


For RJ45 you can find several types of cables in stores. They vary depending on the internal architecture and the type of application for which each one stands out:

  • > UTP: designed to be combined with unshielded twisted pair cable. Its price is very low and easy to use, but they can produce more errors than other types of cables and have limitations to work over long distances without signal regenerators. Therefore, they would be good for connecting nearby devices and where errors are not critical.
  • > FTP: designed to combine with twisted pair cable and global shield. This protection greatly improves the reliability of the cable for transfers, since they generate a screen like that of the coaxial cables of the TV antennas. They will be a little more expensive than UTPs, but they are better for longer distances and where errors are more critical.
  • > STP: designed to be combined with a special version of twisted pair cable that uses metallic protection to shield and shield the cable (of each pair and of the whole assembly). It is the most expensive of all, but also the one that gives the best results.