Introduced in 1998, this made the distinction between uplink and normal ports and manual selector switches on older hubs and switches obsolete. Main article: Medium Dependent Interface § Auto MDI-X The polarity of each pair is not swapped, but the pairs crossed as a unit: the two wires within each pair are not crossed. Such a cable will work for 10BASE-T or 100BASE-TX. A crossover cable may also be used to connect two hubs or two switches on their upstream ports.īecause the only difference between the T568A and T568B pin and pair assignments are that pairs 2 and 3 are swapped, a crossover cable may be envisioned as a cable with one modular connector following T568A and the other T568B (see TIA/EIA-568 wiring). This wiring scheme constitutes a crossover cable.

Since 10BASE-T and 100BASE-TX use pairs 2 and 3, these two pairs must be swapped in the cable. One terminal may be connected directly to another without the use of a switch or hub, but in that case, the crossover must be done in the cabling. A standard straight-through cable is used for this purpose where each pin of the connector on one end is connected to the corresponding pin on the other connector. When a terminal device (with an MDI port) is connected to a switch or hub, this crossover is done internally in the switch or hub ( MDI-X port). The 10BASE-T standard was devised to be used with existing twisted pair cable installations with straight-through connections.

This requires that the transmit pair of each device be connected to the receive pair of the device on the other end. The 10BASE-T and 100BASE-TX Ethernet standards use one wire pair for transmission in each direction.

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