Copper based, twisted pair ethernet terminations come in 2 different flavors recognized by ANSI, TIA and EIA. T568A and T568B. You may have heard the term crossover cable which is a cable terminated with both standards on the 2 opposing ends. All “normal” cables have the same termination on both ends also known as “1 to1”. T568B tends to be more widely used in normal twisted pair cable manufacturing than T568A. Although there is no apparent performance difference between the two there is still some debating in the industry as to which one is better.

Twisted Pair Pin Configurations

The only difference between T568A and T568B wiring standards is the orientation of the green and orange wire pairs. You can see in the attached image that pins 1 and 2 swap orientation with pin 3 and 6. Some older equipment uses standard “A” which might require you to use a crossover cable while using a new computer. Crossovers are also useful if connecting 2 computers together without a switch in between. Nowadays there is rarely a need for crossover because gigabit switches and NIC cards started auto detecting the pin configuration and started doing the pin reconfiguration within the electronic chip electronically. This technology is called auto-MDIX which stands for automatic medium-dependent interface crossover.