Cabling · Networking
RJ45
Also known as: Ethernet Jack, 8P8C
The standard 8-pin connector used for Ethernet — the rectangular plastic plug on every Ethernet cable and the matching jack on switches, routers, and computers.
RJ45 is technically an 8P8C (8-position, 8-contact) modular connector, but everyone calls it an RJ45. It's been the standard physical interface for Ethernet since the early 1990s, supporting everything from legacy 10Mbps to modern 10Gbps connections over twisted-pair copper cable.
The eight pins carry four twisted pairs. In modern Ethernet (1Gbps and above), all four pairs carry data simultaneously. At lower speeds, only two pairs are used for data.
Wiring standards: T568A vs T568B
Two wiring schemes define how the eight wires map to the eight pins. Both work; what matters is consistency — both ends of a cable must use the same standard, and a network should stick to one throughout.
T568B is the more common choice in North America. T568A is common in government and some international installations. Mixing the two on opposite ends of a cable produces a crossover cable — used for direct device-to-device connections without a switch, though modern equipment generally handles this automatically via Auto-MDIX.
Cable categories
The RJ45 connector is compatible with all twisted-pair Ethernet cable categories. The cable spec — Cat5e, Cat6, Cat6a — determines maximum speed and distance, not the connector itself.