What is a crossover cable and what is it used for?
Cabling standard defines one pair of conductors as transmit pair and one pair of conductors for receive pair. When terminal devices are connected to a switch or hub, the cross over is done internally within the switch or hub, the cross over are done internally without a hub or switch, a crossover cable must be used. 10BaseT and 1000BaseTX crossover only require crossing of Pin 1/2 with Pin 3/6. For Gigabit crossover, T4 crossover is required. In addition of crossing Pin 1/2 with Pin 3/6, Pin 4/5 must cross with Pin 7/8. T4 crossover is backward compatible for 10BaseT and 1000BaseTX crossover.
