for two devices to communicate, the transmitter of each device must be connected to the receiver of the other device.the crossover function is usually implemented internally as part of the circuitry in the device. computers and workstation adapter cards are usually media-dependent interface ports, called mdi or uplink ports. most repeaters and switch ports are configured as media-dependent interfaces with built-in crossover ports, called mdi-x or normal ports. auto uplink↑tm automatically senses which connection, mdi or mdi-x, is needed and makes the right connection.

    figure c-1 illustrates straight-through twisted pair cable.

   

    key:

    a = uplink or mdi port (as on a pc)

    b = n4ormal or mdi-x port (as on a hub or switch)

    1, 2, 3, 6 = pin numbers

    figure c-1. straight-through twisted-pair cable

    figure c-2 illustrates crossover twisted pair cable.

   

    key:

    b = normal or mdi-x port (as on a hub or switch)

    1, 2, 3, 6 = pin numbers

    figure c-2. crossover twisted-pair cable