What are the two Standards for patch cable pin configuration?

Answer 1

One is straight-through, meaning that pin 1 on one plug goes to pin 1 on second plug and so on. This type of cable is used 99% of the cases, when you want to connect a computer (or other networked device) to a hub or switch. There can be 1-3 (or even more) such cables on the way, for example:

- 1 cable connecting a computer to a desktop switch directly

- 3 cables: one to the wall socket, next from wall socket to the patchpanel in the cabinet (socket-to-socket cable, instead of plug-to-plug, but the principle is the same), and third from patchpanel to the switch inside the cabinet.

The socket in a hub/switch is internally connected in such a way, that transmitted signal (TX pair) from the computer is fed to the receiver (RX), and vice versa: RX pair from the computer is wired to the TX output. This makes it possible to use straight-through cables in any necessary quantity, because nothing gets changed on the way.

The second type is a "crossover" cable. It is wired in such a way, that the RX pair on one side is connected to the TX pins on the other side, and the TX pair is connected to the RX pins. It is used in special cases, for example if you want to connect:

- two computers with each other only

- two hubs/switches together to extend the network

- a router or modem-router with a computer only

This type of cable can be extended, but only using straight-through cable, because an even number of crossover cables (for example 2) will result in crossing twice, which will bring the signals back to the same position, hence not crossing at all.

Modern network equipment usually has auto-sensing network ports, which reconfigure themselves automatically based on the signals they sense in the cable, so the necessity of using crossover cables is diminished. It will usually be written somewhere in a form similar to "Auto MDI/MDIX".