Was it perhaps DEC Baseway[1] system? It would arguably qualify as a form of DCS, with central VAX servers and running high level software, PDP-11 "shop floor" computers, which in turn talked with PLCs and related devices.

And additionally, TCP/IP was an optional layered product - either DEC's own UCX (Ultrix Communication eXtensions) or 3rd party

[1] https://bitsavers.org/pdf/dec/vax/vms/baseway/

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intrasight 17 hours ago | parent [-]

I guess they didn't buy the optional network software.

I remember working with this engineer writing in the lower level TCPIP stack on the deck - maybe in Fortran? Anyway, he didn't understand why he wasn't getting all the data transmitted and while I was no expert in TCP/IP, I was already familiar with packets and maximum segment size (MSS). I remember being impressed that he banged out a network stack in a couple weeks.

	▲	p_l 11 hours ago \| parent [-]
		Baseway, and various other industrial control systems that also ran on VMS and related, tended to either use DEC-suggested (DECnet) protocols or implemented custom Ethernet-layer ones