Accidentally flipped a pair of Ethernet wires. Why does it still work?
Dec 11
I pulled off my patch panel today to discover that I had originally punched down the green pair (3/6) incorrectly?
I never noticed because it all just worked? If it matters, the wiring is CAT6, in a CAT6A patch panel. I pulled off one of the wall jacks to ensure it’s wired correctly... and it is.
I just want to know why it worked?
1 answer
Accepted answer · original discussion
Dec 11
Ethernet TX and RX signals (Green and Orange pairs) are transmitted in differential mode aka "balanced":
https://en.wikipedia.org/wiki/Differential_signaling
https://en.wikipedia.org/wiki/Ethernet_physical_layer
https://en.wikipedia.org/wiki/Ethernet_over_twisted_pair
When using differential signaling the information is carried by the voltage difference (electrical pulses) betweeen conductors. The signal polarity (being which of the two conductors is the "positive" one) is important only in the case the receiver device is not able to auto detect it and automatically invert the received pulses decoding. Most if not all of the modern Ethernet chips are able to auto-sense polatiry. As an example, the following model is able to do automatic polarity detection and correction: http://ww1.microchip.com/downloads/en/devicedoc/8720a.pdf
The so called "polarity fault" has been addressed by the IEEE 802.3 Note that since 100BASE-TX specification, polarity is no more used in receiver.
The following link reports a more detailed analysis:
http://ww1.microchip.com/downloads/en/AppNotes/AN127-UNG.pdf
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