alt Hacker News1000Base-T uses two pairs per direction, actually. It's full duplex. Each port sees two TX and two RX pair.
There are four pair of wires in the cable. If you use all of them for TX, you can't receive.
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anonymousiam • today at 8:57 PM
1000Base-T uses four pairs in both directions at the same time. It does this through the use of a hybrid in the PHY that subtracts what is being transmitted from what is received on the wires. 802.3ab is a fairly complicated specification with many layers of abstraction. I spent a few months studying it for a project about a decade ago.
direwolf20 • today at 2:36 PM
That's not true. https://en.wikipedia.org/wiki/Gigabit_Ethernet#1000BASE%E2%8...
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> There are four pair of wires in the cable. If you use all of them for TX, you can't receive.
No, you absolutely can use them all for transmit and receive at the same time. The device at each end knows what signal it is transmitting, and can remove that from the received signal to identify what has been transmitted by the other end.
This is the magic that made 1000Base-T win out among the candidates for Gige over copper, since it required the lowest signaling frequencies and thus would run better over existing cables.