Yamaha was quite good at glomming networking features on top of MIDI. They did it in a few ways - I remember double-taking in a Tokyo ops room when I saw a Yamaha C1 being used as a server for a bunch of CX5M's .. traditionally a game or music-making setup, but in this case it was electronic mail and bulletin-boards .. in Japanese ..
Anyway MIDI lives on today because its a great little easy networking protocol, easy to implement and suddenly your device can communicate to a lot of other interesting things..
So it was MIDI! I suspected as much but could not find any documentation.
Funny that since it was the first network I've seen I was naturally expecting all networks to use mini-DIN cables and daisy chaining. The next network, many years later, was a co-axial setup - my mind was blown.
Anyway MIDI lives on today because its a great little easy networking protocol, easy to implement and suddenly your device can communicate to a lot of other interesting things..