An Ethernet crossover cable is a type of Ethernet cable used to connect computing devices together directly. It is most often used to connect two devices of the same type: e.g. two computers (via network interface controller) or two switches to each other. By contrast,patch cables or straight through cables are used to connect devices of different types, such as a computer to a router (or network switchor hub).
Many devices today support Auto MDI-X capability, wherein a patch cable can be used in place of a crossover cable, or vice versa, and the receive and transmit signals are reconfigured automatically to yield the expected result.
The RJ45 connector is standardized as the IEC 60603-7 8P8C modular connector with eight conductors. The RJ45S, a similar standard jack once specified for modem or data interfaces, uses a mechanically-keyed variation of the 8P8C body with an extra tab that prevents it from mating with other connectors; the visual difference from the more-common 8P8C is subtle. The original RJ45S keyed 8P2C modular connector had pins 5 and 4 wired for tip and ring of a single telephone line, and pins 7 and 8 shorting a programming resistor,[7][8] but is obsolete today.
An installer may wire the jack to an arbitrary pinout, or use it as part of a standardized generic structured cabling system such as ISO/IEC 15018 or ISO/IEC 11801, using 8P8C patch panels for both phone and data wiring.
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