[HECnet] DECnet et al

[Bob Armstrong]

When did DECNET first appear? 

  Mid-1970s, depending on which version ("Phase") you consider to be
"DECnet".   I'm sure someone will provide a more specific date.

using what means to connect each system.

  Point to point serial (note that doesn't mean RS-232!) links (rarely
parallel) using various means for the actual physical connection.

  DECnet definitely predates Ethernet by many years, if that's your point.

Bob