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A medium dependent interface crossover (MDIX) is a version of the medium dependent interface (MDI) enabling a connection between corresponding devices. An MDI port or uplink port is a port on a switch, router or network hub connecting to another switch or hub using a straight-through cable rather than an Ethernet crossover cable. Generally there are one to two ports on a switch or hub with an uplink switch, which can be used to alter between an MDI and MDIX interface.
An MDIX is a female 8 Position 8 Contact (8P8C or RJ45) modular port connector on a router, switch, hub or computer. It uses a straight-through cable which is a network cable that connects pins 1 and 2 (transmitting) on an MDI device to pins 1 and 2 (receiving) on an MDIX device. The “X” or crossover is in reference to the transmitting wires (MDI), which must be connected to the receiving (MDIX)wires to “crossover” signals.
This term is also known as MDI crossover (X).
Generally switches and hubs use an MDIX interface. Routers use an MDI interface in a workstation or PC environment. Newer technology for hubs, switches and routers automatically detect the appropriate cable connection type by the use of automatic medium-dependent interface crossover (Auto-MDIX) or Auto Uplink. With Auto-MDIX straight-through cable and Ethernet, crossover cable can be used. Switches and hubs not having Auto-MDIX will typically have one port that will not cross the line or crossover.
MDIX is a version of the medium dependent interface (MDI), which is a module of the media attachment unit (MAU). The MAU is a transceiver converting signals on an Ethernet cable for which it transmits and receives attachment unit interface (AUI) signals. The standard for the MDIX is the MDI standard. It uses straight through twisted pair cabling allowing crossover (X) signals to be transmitted and received without the need of crossover cable. Older switches and hubs use the MDIX interface. Routers use an MDI interface. Newer devices automatically detect the proper cable connection type by using automatic medium-dependent interface crossover (Auto-MDIX) or Auto Uplink. All 1 Gb or 10 Gb devices and some 10/100 (10Base-T, 10Base-TX) devices have Auto-MDIX. A device that has Auto-MDIX can use either Ethernet crossover cable or straight-through cable. A hub or switch that does not have an Auto-MDIX feature needs to have one port, which will not crossover or cross the line. However, a gigabit Ethernet typically has 2 Auto-MDIX ports connected together.
Auto-MDIX uses automatic line sensing in the ports called auto sensing. This feature eliminates the need for special crossover cable, separate MDI and MDIX ports, and switches requiring selection for particular devices. Auto-MDIX configures the cable connection automatically, allowing both crossover and straight-through cabling to be used. When the Auto-MDIX interface is connected, it will correct any improper cabling. To ensure the speed is correct, the duplex setting needs to be set to "auto.”