A "straight" or "straight-through" cable, on the one hand, and a "crossover" cable, on the other, are the same type of cable between their connectors. The difference is the wiring in one of the connectors of the cable. A straight-through cable uses the same pin configuration at both ends. A crossover cable swaps the pin allocation for some of its constituent wires.
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Several types of cable are used for networks, but the crossover cable can only be implemented with a composite cable, which is any cable made up of a bundle of wires. Coaxial cable, for examples, cannot implement this technique as it has one solid core. Crossover cables requires a number of inner wires that can be crossed over. The most popular cable used for networking is the Unshielded Twisted Pair. As this cable contains eight separate wires, it is ideally suited to the creation of crossover cable.
Unshielded Twisted Pair cable, or UTP contains eight wires, each of which has its own colour coded plastic casing. The important wires for crossover cabling are the Transmit Positive (TX+) wire, which is white with a green stripe; the Transmit Negative (TX-) wire, which is green; the Receive Positive wire (RX+), which is white with an orange stripe; and the Receive Negative wire, which is orange.
In a straight-through cable, the wiring of the four transmit and receive wires goes from one connector to the connector at the other end, connecting to the same pin in each connector. TX+ goes to pin 1, TX- goes to pin 2, RX+ goes to pin 3 and RX- goes to pin 6.
In crossover wiring the connectors at each end are treated differently. The first connector is wired exactly the same as in the straight wiring guide: Pins 1, 2, 3 and 6 receive TX+, TX-, RX+ and RX- respectively. The other connector is the crossover implementation. The transmit wires go to the receive pins and the receive wires go to the transmit pins. So RX+ goes to pin 1, RX- goes to pin 2, TX+ goes to pin 3 and TX- goes to pin 6.
Computers connect to hubs on networks. Computers always send data down the transmit wires and listen for incoming data on the receive wires. The manufacturers of hubs know this, so the contacts inside the cable socket on the hub is reversed with the receive contacts touching the transmit contacts in the plug and the transmit contacts touching the receive plug contacts. By this method the hub receives the computers transmit and the computer receives the hub's transmit. This scenario requires straight cable. When a computer connects to another computer directly by cable, or if a hub connects to another hub, crossover wiring switches the receive and transmit paths to ensure that transmissions are made on the wires the receiver is listening to.
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