MDIX
From Wikipedia, the free encyclopedia
Medium dependent interface crossover or MDIX (the “X” representing “crossover”) is an Ethernet port connection on a router, hub or switch. Straight through cables connect pins 1 & 2 (transmit) on an MDI device to pins 1 & 2 (receive) on an MDIX device. Similarly pins 3 & 6 are receive on an MDI device and transmit on a MDIX device. The X refers to the fact that transmit wires on an MDI device must be connected to receive wires on an MDIX device. As a rule, end stations (i.e., PCs or workstations) use an MDI interface and routers, hubs and switches use MDIX interfaces. Newer routers, hubs and switches (including all 1 Gigabit and 10 Gigabit devices) use Auto MDI/MDIX to automatically switch to the proper configuration once a cable is connected. The other four wires are used but are not crossed since Auto MDI/MDIX is mandatory at the higher speeds. See Ethernet over twisted pair for more details on cables and standards.
