MDI/MDIX

medium-dependent interface/medium-dependent interface crossed

A type of Ethernet port connection that uses twisted-pair cabling, as specified in the IEEE 802.3 standard. Network adapter cards on computers typically connect to a network using RJ-45 interface ports that use pins 1 and 2 to transmit, and pins 3 and 6 to receive. Uplink ports on hubs and switches use the same pin assignments. Normal ports on hubs and switches use the opposite pin assignment: pins 1 and 2 are used to receive, and pins 3 and 6 are used to transmit. Such ports are called MDIX ports.