Communication or communications?

I have my friend in a headlock about this one. The subject is the transfer of data via a cable (data communciation) between two devices. He wants to say "If communications are...") and I feel "If communication is ...." is correct.
I know communications is correct in some cases, but to me it implies a distinctly countable subject. In our case, we're using it for data communication, which to me is an uncountable stream (I mean are you going to count each piece of data as it flies by?)
Are there any rules about this one?

Here is the full sentence.
"The vacuum pump cannot be started and plasma ignition is not possible if communications are not established between the PC and the main unit."
I want to say-
"The vacuum pump cannot be started and plasma ignition is not possible if communication is not established between the PC and the main unit."

(Now that I think about it, I should probably say:
"Communication must be established between the PC and the main unit prior to starting the vacuum pump and igniting the plasma.")

Checked out M.Webster's site and they say:

3 a : a process by which information is exchanged between individuals through a common system of symbols, signs, or behavior ; also : exchange of information b : personal rapport
(and also)
4 plural a : a system (as of telephones) for communicating b : a system of routes for moving troops, supplies, and vehicles c : personnel engaged in communicating

They seem to be saying when communication relates to humans, use "communication". When it relates to something else, use "communications".
But am I right that this implies a LOT of distinct entities communicating? In my case it is just the PC and the main unit, similar perhaps to two persons, or 3a.