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I want to power on/off an (Gigabit) Ethernet connection physically by using some circuit. The main idea was to use a transistor with the Raspberry Pi GPIO to switch an Ethernet cable. The schematics are in the link below.

Could this work? Or do you have any alternative ideas on the matter? Which ground could the cable and the Transistor + RPi use?

Schematics:

enter image description here

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What do you expect this circuit to do? How would disconnecting a data signal wire in an Ethernet cable power down a device? You need to control power, not data. – Transistor May 13 at 11:06
    
It will be used for an experiment to simulate a physical disconnection of a cable – swinja123 May 13 at 11:49
    
Well read your question title and content again. That is not at all what you have asked. Edit your question and explain exactly what you are trying to do and why. – Transistor May 13 at 13:50
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Sorry but your circuit won't work. As Michael says Ethernet is too sensitive for solutions like that. So here are a few other suggestions that might help.

The simplest solution would be a managed switch that both machines were connected by and then use the Pi to connect to the management interface, via serial or telnet, and tell the switch to close and open the ports as you need.

Or write and install a service on the hosts that when the authenticated Pi sent a message to them the services used operating system functions to disable the network interfaces. Obviously there is a problem with this solution when it comes to turning the connection back on.

You might be able to use a USB Ethernet adapter on the Pi to create your own two port switch, then bridge the connections using the Pi's OS. The Pi can then enable and disable the connections at will, but I'm not sure what the performance would be like.

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Thank you for your comprehensive answer, I will definetely look into some of your suggestions – swinja123 May 13 at 13:28
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The circuit you have posted above will not work because Ethernet signals are isolated at the jack i.e. there is no direct current path from the wires in the cable to the traces from the PHY on the PCB.

You may also run into trouble with signal integrity going via a transistor, the transistor will introduce too much distortion to the signal in the cable and either cause the connection to fail entirely or run at a reduced rate.

A better approach would be to use a relay as this will allow you to keep the control coming from the PI isolated from the Ethernet cable, you may still run into excessive signal distortion, check out this question for more information:

How can I make a device that will remotely disconnect an Ethernet port?

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Thank your very much for you great answer. Could you please explain it in more detail why the circuit won't work? Thank you very much – swinja123 May 13 at 13:29

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