I am setting up ethernet in a friends house with cat 5 cabling. I do not do this professionally but I have made like 20 patch cables and installed about 20 wall sockets before in my own house.
My friend's house has two existing RJ45 wall sockets with an (old) existing cabling between them. I made two patch cables using the T-568-B wiring system and tested them both using a Goobay CAT-Network-Tester TP III. The tester goes through the pins and the other end lights the leds in the same order from 1 to 8.
When I connect all three segments together: - patch cable 1 - wall socket 1 - existing cable inside the walls - wall socket 2 - patch cable 2 and set up the transmitter in one end of patch cable 1 and the terminator at the end of patch cable 2, the tester shows only lights 2, 3, 4, 6, 7, 8.
This seems to indicate, that only green and brown pairs are used. However, cat 5 is supposed to work with green and orange.
So how come this connection works?
update: went to this friends house and checked the speed, the speed is 45Mbps download and 32 Mbps upload which is the same as in other parts of the house. So I am assuming that it is not working on one pair only. The physical layer must somehow detect that non-standard wiring is used and adapts to that