Re: Rings
The original ethernet was 3 MBits and used black RG11U foam 75 ohm impedance (with 50 ohm connectors!) cables with vampire taps. The speed of propagation was 66% of the speed of light. The design of the cable interface to the vampire taps was done by Tat Lam as the PARC people weren't really analog hardware experts. The collision detect would not work on very high-speed networks because of the speed of light/propagation. Tests showed 99% utilization with an offered load of 300%. We had multiple protocols running on the net: pup, leaf sequin, paulos, xns, ip, breath of life etc. with some other protocols for playing TREK or mazewars.
Some of these protocols also existed on the ARPANET
Eventually we got a 10 MBit cable with 50 ohm impedance.
TCP/IP didn't have a field to indicate other protocols so we used an illegal length to indicate the other protocols.
The original ALTO computers had a hard-wired 8-bit address which had to be changed when changing nets to avoid duplicating some other machine on the net. I think that the maximum number of nets was 255. It was hard tracking down another machine with the same address. The best strategy was to check who just received an ALTO.