What is an RJ45 Gigabit LAN Port?

By Stephen Byron Cooper

Sockets on computers and network devices are known as “ports.” A network port is also called a LAN port -- LAN stands for local area network -- which is an industry term for a private network. The leading set of standards for the physical properties of LANs is called Ethernet. The Ethernet recommendations evolve over time, each new addition creating faster and more efficient networks. The latest series of Ethernet standards covers networks that can transfer data at more than a thousand million bits per second -- a gigabit LAN. RJ45 is the common name for connecting the network cable to the computer.


The RJ45 connector is the most common form of plug/socket design used in networking today. Computers shipped from the manufacturer with a network adapter installed always have an RJ45 port. The name is not completely accurate as it is a code allotted to a type of telephone jack by the US Federal Communication Commission. The “RJ” in RJ45 stands for “Registered Jack” and all telephone connectors approved for use in the United States have an RJ code. The true RJ45 plug has eight pins and two contacts. In Ethernet applications, the plug has eight pins and eight contacts. As the RJ designation refers to the wiring plan and not the design of the plug, the Ethernet plug is not an RJ45. However, it looks exactly like one, and so everyone calls it RJ45.

LAN Port

LAN ports are also known as Ethernet ports, network ports, RJ45 jacks, network socket or network card. The socket looks similar to a telephone socket, only it is a little wider. Inside the socket eight metal strips at the bottom connect with corresponding strips in the plug. When the plug is inserted into the port it is locked into place by as plastic spring. This plug holds a connection by keeping the metal strips in the plug and socket in contact. The LAN port connects directly to the computer's network adapter and it is this connection between network adapters over cable that forms a network.


The Ethernet standards have been published as open standards since 1983. The controlling authority is the Institute of Electrical and Electronics Engineers. All Ethernet standards are published under the code 802.3 followed by one or two letters to indicate a sequence. Each recommendation forms a description of hardware requirements that the 802.3 committee has investigated as the best interconnection of technologies to produce improved network performance. The standards recommend different cable types for each level of performance. The most common form of cable in use today for Ethernet networks is unshielded twisted pair, which is terminated by the RJ45-style connector.

Gigabit Ethernet

The Ethernet recommendations for gigabit networks include four types of cable: twin-axial cable, unshielded twisted pair and single-mode and multi-mode fiber optic cable. Of these four types, only UTP uses the RJ45-style plug and could connect to the RJ45 LAN port of a computer.