A crossover cable connects two devices of the same type, for example DTE-DTE or DCE-DCE, usually connected asymmetrically (DTE-DCE), by a modified cable called a crosslink. Such distinction of devices was introduced by IBM.

The crossing wires in a cable or in a connector adaptor allows:

• connecting two devices directly, output of one to input of the other,
• letting two terminal (DTE) devices communicate without an interconnecting hub knot, i.e. PCs,
• linking two or more hubs, switches or routers (DCE) together, possibly to work as one wider device.

  Examples

  • a Null modem of RS-232
  • Ethernet crossover cable
  • Rollover cable
  • A loopback is a type of degraded "one side crosslinked connection" connecting a port to itself, usually for test purposes.

  Use crossover cables for the following connections: Switch to switch, Switch to hub, Hub to hub, Router to router, PC to PC, Router to PC

  [edit] Other technologies

  Some connection standards use different balanced pairs to transmit data, so crossover cables for them have different configurations to swap the transmit and receive pairs:

  • Twisted pair Token ring uses T568B pairs 1 and 3 (the same as T568A pairs 1 and 2), so a crossover cable to connect two Token Ring interfaces must swap these pairs, connecting pins 4, 5, 3, and 6 to 3, 6, 4, and 5 respectively.
  • A T1 cable uses T568B pairs 1 and 2, so to connect two T1 CSU/DSU devices back-to-back requires a crossover cable that swaps these pairs. Specifically, pins 1, 2, 4, and 5 are connected to 4, 5, 1, and 2 respectively.
  • A 56K DDS cable uses T568B pairs 02 and 04, so a crossover cable for these devices swaps those pairs (pins 01, 02, 07, and 08 are connected to 07, 08, 01, and 02 respectively).

  A null modem cable.

  An Ethernet crossover cable.