it had things called 'flows' which were half way between pure
datagrams (i.e. no setup - you just stick the right destination address in the
header and send it off) and VCs (read the RFCs if you want to kow why),
In that connection I have always admired Padlipsky's RFC 962, which exploits the existing TCP architecture to do just this. So simple, so easy, so Unixy.