What Is the Purpose of an RJ45 Port?

The RJ-45 port on a computer is a socket enabling a connection to a network. The RJ-45 jack is a form of connector that was originally designed for telephone connections. The plug configuration was adapted for use with Unshielded Twisted Pair cable, specifically to follow Ethernet standards.

1. Ethernet

   • Ethernet is the most widely implemented set of standards dictating the physical properties of networks. These properties include the cable type and connector configuration. The RJ-45 socket is the most common form of connector used for Ethernet networks. Although Ethernet also recommends other cable types with other connectors, the RJ-45 plug is so widely used for Ethernet networks that it is often referred to as the "Ethernet jack."

   Specification

   • The RJ-45 is always used in conjunction with Unshielded Twisted Pair cable. The "RJ" of RJ-45 stands for "Registered Jack. The Registered Jack series was originally devised for the US Federal Communication Commission who wished to standardize telephone connectors. The RJ specifications refer to the wiring plan of each connector. The RJ-45 used for networks does not conform to the RJ-45 specification, and so is not, strictly speaking an RJ-45, although it looks like one. The original RJ-45 connector contains eight pins, but only two contacts. This is written in shorthand as 8P2C. The Ethernet implementation uses the same plug, but has eight pins and eight contacts. This is known as 8P8C.

   Network Cable

   • The RJ-45 plug terminates Unshielded Twisted Pair cable. Like the connector, UTP is so widely implemented for Ethernet networks that it is commonly known as Ethernet cable. The cable contains eight wires, which makes the eight pins of the RJ-45 plug suitable for use with this cable type. Although Ethernet networks recommend the use of this eight wire cable, only four of the wires actually ever carry a charge.

   Paths

   • The eight contacts within the computer socket touch eight metal contacts within the plug head. Each contact leads to a pin, which, in turn, leads to a wire. Two wires are the positive and negative lines of the transmit path, on which the computer sends data. Computers do not listen for incoming data on these wires. Instead, they expect to receive in data on two other lines, which are the positive and negative paths of the receive path.