You are mentioning two things. 1) yes, they send send signals, and their "inverse" over a pair of cables. That's guaranteed by the use of transformers on your n

You are mentioning two things. 1) yes, they send send signals, and their "inverse" over a pair of cables. That's guaranteed by the use of transformers on your network card/network switch. Current that the transformer sends in one line of a pair, has to be returned in the other pair. https://www.google.de/search?q=ethernet+transformer&tbm=isch https://www.google.de/search?q=ethernet+transformer&tbm=isch On an old 10MBit or 100MBit/s card (10BaseT, 100BaseT) on each device there will be one pair to send data out, and one to receive data. This uses up 4 pins on your RJ45 connector, the other 2 are unused. The pair that is used on your network card to send out data are pins 1 and 2. The pair that is used on your network card to receive data is on pins 3 and 6. The 2nd thing you mention are the two standards TIA/EIA-568 assigns colors to pins, and they have a version A and B where the colours of pair 1/2 and pair 3/6 are swapped. https://en.wikipedia.org/wiki/TIA/EIA-568 https://en.wikipedia.org/wiki/TIA/EIA-568 Hence, when you have a cable where one side is wired according to "A" and the other is wired according to "B" you have something that, in the old days, was called a cross-cable, which you could use to directly connecto two computers with each other, without having a hub or switch in between. Which is very useful, especially if you'd connect e.g. two switches in two buildings with each other. Tx 568A 568B Tx 1 o---white----\ /---white---o 2 o---green---- \ /----orange--o X 3 o---white---- / \----white---o 6 o---orange---/ \---green---o Rx Rx But because miswirings regarding the two color schemes were so frequent, and connecting routers/switches/computers directly using "straight" cables was so convenient, most devices manufactured after the 90s can swap these pairs internally automatically. Hence no matter if you have a strait or cross-cable, or a miswired 568A/B installation computers will just function fine. With 1000BaseT (Gigabit-Ethernet) data is transmitted and received on all pairs simultaneously, and also this miswiring is automatically detected and taken into account.