The migration of LAN cabling infrastructure to the use of twisted pair cable has been accompanied by a significant increase in the use of the modular RJ-45 connector. Today most network adapter cards, hubs and concentrators are manufactured to accept the use of the RJ-45 connector.

One of the first networks to use the RJ-45 connector was 10BASE-T, which represents a 10 Mbps version of Ethernet designed for operation over unshielded twisted pair (UTP). Since UTP cable previously installed in commercial buildings commonly contains either three or four wire pairs, the RJ 45 connector or jack was selected to be used with 10BASE-T, even through this version of Ethernet only supports the use of four pins.

Although 10BASE-T only uses four of the eight RJ-45 pins, other versions of Ethernet and different LANs use the additional pins in the connector. For example, a full duplex version of Ethernet requires the use of eight pins.

Thus, the original selection of the RJ-45 connector has proven to be a wise choice. Ethernet is a termthat actually references a series of local area networks that use the same access protocol (CSMA/CD) but can use different types of cable.

Early versions of Ethernet operated over either thick or thin coaxial cable. The attachment of an Ethernet workstation to a thick coaxial cable is accomplished through the use of a short cable which connects the workstation to a device known as a transceiver. This connection is accomplished through the use of a DB-15 connector.

The attachment of an Ethernet workstation to a thin coaxial cable requires the use of a T connector on the coax. The T connector is then cabled to a BNC connector on the network adapter card installed in the workstation.

Recognizing the fact that a workstation could be connected to a thick or thin coaxial cable or a twisted-pair based network manufacturers would have to support three separate types of adapter cards based upon different connectors required.

Rather than face this inventory nightmare, most Ethernet network adapter card manufacturers now incorporate all three connectors on the cards they produce. Not only does this type of card simplify the manufacturer’s inventory but, in addition, it provides end-users with the ability to easily migrate from one wiring infrastructure to another without having to replace network interface cards.

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