[watersb]

Thanks, that explains it quite nicely.

1990s AppleTalk networks could work over a single pair. I ran a network with hundreds of Macs for a tech company. Ten buildings in a small campus.

Still remember the day the fire-alarm techs punched down over one of the Macs in the executive office. Not much of a network signal when there's 24 Volts on the same line.