MDI Port Definition

A medium dependent interface port (MDI port), also called an uplink port, is a port (i.e., connector) on a network hub or on a network switch that is used to connect to other hubs or switches via a conventional straight-through cable, i.e., without requiring a crossover cable.

A crossover cable is a type of twisted pair copper wire cable for LANs (local area networks) in which the wires on the cable are crossed over so that the receive signal pins on the RJ-45 connector on one end are connected to the transmit signal pins on the RJ-45 connector on the other end. Its purpose is to allow the direct connection two hubs or switches.

An MDIX (MDI crossover) port is a version of an MDI port that enables connection between like devices (e.g., two hubs) by crossing the transmit and receive circuits. The straight-through cable connecting an MDI port on one hub or switch is inserted into an MDIX port on the other hub or switch. Both MDI-to-MDI and MDIX-to-MDIX connections use crossover cables.

There are typically one or two ports on a hub or switch that the user can toggle with a small switch between MDI and MDIX operation.

Created October 27, 2005.
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