This is really intriguing. I was recently pondering something related: 10/100 ethernet only uses two pairs, one in each direction. Of course the jack has four

This is really intriguing. I was recently pondering something related: 10/100 ethernet only uses two pairs, one in each direction. Of course the jack has four pairs, and the cable has four pairs and gigabit uses all four. But, if you're only using 10/100, it's trivial to split the jack on either end of a run, and carry two "ports" worth over a single cat5 cable. However, this requires a second splitter at the switch end, like so: https://lib.store.yahoo.net/lib/cablesonline/NETWORK13.JPG https://lib.store.yahoo.net/lib/cablesonline/NETWORK13.JPG Would it be possible for a suitably-bastardized GigE PHY to drive the four pairs as two independent "ports" of 10/100, assuming such a splitter was just on the far end, but the cable on the near end was plugged directly into the switch? Don't ask about practical applications, I really have none in mind. It just struck me as a perverted and wrong thing to do, therefore it must be done. (And on that note, since GigE really runs the four pairs as four nearly-independent bidirectional channels and then merges their capacity afterward.... could you get four 250Mbps "ports" out of such a thing? By routing all four pairs to four separate devices, each of which is also running this bonkers implementation? Essentially reinventing single-pair ethernet (yet again yet again yet again yet again) using all stock PHYs. This would require cooperating devices on both ends of the link, but the prior idea could be used with stock 10/100 devices.)