...
The RJ45 connector is the standard to connect to an ethernet cable with 8 pins that correspond to 4 bi-directional differential pairs. In gigabit ethernet, all 4 differential pairs are used, and a minimum of Category 5 cable is required. Magnetic Transformers are required for these differential pairs to isolate the communication wires from the rest of the system and ensure that their signal isn’t corrupted by any faults elsewhere. They can either be integrated with the RJ45 connector or added externally in the schematic design.
...
Gigabit Ethernet uses 4 differential pairs to transmit and receive data. Each of these pairs is bi-directional so they can send and receive data at the same time., and therefore backwards compatible with slower methods of ethernet. The naming and colour codes for these pairs are seen below:
...