Looking for help designing a circuit.

I'd like to detect when an end point device communicating via Ethernet gets plugged into an RJ-45 connected to the acceptable distance of a CAT-5e+ cable.

The detection should occur without impacting the signal quality. The circuit needs to pass the signal to another end point device without either end point devices being aware of the detection.

This is a very high level overview. I can provide more details if this is confusing.

Thanks in advance!

You can use a discovery routine from the switch that's providing Ethernet connectivity to the end device - why won't that work?

Or you can just look at the green lights on the individual ports on your Switch or router... which only light doing those conditions. Depending on exactly what you are needing this for.

There is a lot more to this than just physical connectivity...but passing and recieving properly formatted valid packets of data. You aren't going to build a simple hardware circuit that can do that part of it. Not without incorporating preconfigured subassemblies to process that part.

THere is the software solution that ebaines offered.