Thanks for expanding on my knowledge. I have only experience implementing support for talking to a fluid property sensor in an industrial process and not much more. Thankfully, I might add.

Looked at it like a fixed phy layer with some parts of the messaging fixed as well, although now that you brought it up, I remember adding J1939 support too.

Ugh, it was, in my opinion, a bit-hacked mess :) I can really appreciate when things that despite being messy and hackish, solve real, actual problems, and for that, I thank thee, CAN-bus :).