Twisted Pair Cabling – Crossover Cable

Twisted-Pair Cabling – Crossover Cable

A crossover cable is used in the following circumstances:
• From a host to a host – MDI to MDI
• From a hub to a hub - MDIX to MDIX
• From a switch to a switch - MDIX to MDIX
• From a hub to a switch - MDIX to MDIX
• From a router to a router - MDI to MDI

Remember that a hub or a switch will provide the crossover function.
However, when connecting a host directly to another host (MDI to MDI),
the crossover function must be provided by a crossover cable.

A crossover cable is often required to uplink a hub to another hub, or to
uplink a switch to another switch. This is because the crossover is performed
twice, once on each hub or switch (MDIX to MDIX), negating the crossover.

Modern devices can now automatically detect whether the crossover
function is required, negating the need for a crossover cable. This
functionality is referred to as Auto-MDIX, and is now standard with Gigabit
Ethernet, which uses all eight wires to both transmit and receive. Auto-
MDIX requires that autonegotiation be enabled.

To create a crossover cable, the transmit pins must be swapped with the
receive pins on one end of the cable:
• Pins 1 and 3
• Pins 2 and 6

Note that the Orange and Green pins have been swapped on Connector 2.
The first connector is using the TIA/EIA-568B standard, while the second
connector is using the TIA/EIA-568A standard.