What is the adapter and what it is not

What is it and what it is used:

Who has moved to the home network cable, that knows you. It has been drawn with difficulty a cable and that was enough and completely. Now to a second device to where you will seek no additional switch, but has the existing switch still a free port.

Here, the adapter is used (namely in a double).
Adapter number 1 comes to the end of the cable to which the switch is located. The two outputs are connected to free ports on the switch.

Adapter number 2 arrives at the other end, there the two devices to the two outputs are connected.

Done. Now one has two compounds with 10 or 100 Mbit via a cable. More then is no longer well.

Why does it work?
The 100Mbit connection requires only two of the four existing pairs. The adapter grinds the second connection so that over the two previously unused pairs of wires running.

What does not work:
1. Gigabit connections (here are all 4 wire pairs required for transmission).
2. PoE (the meinsten injectors supply the device via the unused lines).

My experience with it:
The adapter is simply built that he must just work. And that's what he does.