EIA/TIA-568-A and EIA/TIA-568-B are standards for the contacting of eight-pin Ethernet RJ-45 connectors. In functional terms, there are no differences and the only visual difference is that core pairs 2 and 3 (orange/white & green/white) are swapped round. The only thing that is important here is that contacting is consistently in line with the standards. In Europe, contacting according to A is widespread as the colours match the code of typical telecommunications cables! In the USA, B is more widespread for historical reasons!
