Hi Ian,

I agree with all three of your bullets - points well made.

To step back a bit, the very point of digitally encoding any kind of signal for transmission is to make the base signal more robust in the presence of noise and distortion that always affect analogue electromagnetic signals to some degree. I think we all agree on that

TCPIP, where it applies, adds further robustness to this picture by preventing transmission of data packets containing errors.

Back with the Ethernet signal, there is some inevitable distortion of the component analogue waveforms, certainly including some degree of attenuation and some temporal distortion. That these things will happen to some degree is a certainty, based on long established principles of signal transmission and properties of conductors. Making this un-true would require some basic laws of physics to be broken.

The cleverness in Ethernet design is that it creates a remarkably robust environment that allows data to be passed reliably over distances of upto 100m. The day job of digital encoding and TCPIP (where applicable) in this context is to allow continuous accurate data transmission in the presence of some noise and distortion on the base waveform. This ties back to the basic objective behind digitally encoding a signal.

In Ethernet, whatever percentage of the underlying analogue signal is distorted, while it does no harm to the data stream, contributes additively to RFI noise inside the cable and is passed on relatively transparently down the food chain.

It's worth having a look online for oscilloscope images of Ethernet signals at the downstream end of a cable - you'd be surprised by how much distortion of the original square wave there can be without causing big errors. Just make sure you're looking at images showing a signal after transmission, rather than a fresh signal on the output of a switch, where there would be no meaningful distortion.

It's also quite helpful to look for screen grabs from spectrum analysers, where you can see what I described earlier re the base signal being made up of energy at increasing frequencies and decreasing amplitudes.

Regards,
Dave

808v5, MD600 & DSP7200.1
Dedicated audio mains supply