Looking over a list of various VAX processors, I noticed a reference to a "CI" bus. Poking about in Google I can only find very passing mentions of this, and no details. I suspect this had some other un-acronym name that might work better?
At a certain point in the 1980s, 'I' things were all the rage in DEC.
BI - Backplane Interconnect (the bus in the 8xxx series VAXen - see Wikipedia)
CI - Computer Interconnect (showed up as star coupler for VAXclusters, also to HSC intelligent storage controllers)
NI - Network Interconnect (ethernet to you).
SI - Storage Interconnect - controller-to-disk.
The point was to define a hierarchy of standardized interconnect structure, with different characteristics of speed, operating area, number of nodes supported, etc.)
Figure 1-3 in this manual shows various interconnects, including the CI.
The DEC Technical Journal, number 5, from 1987, has some CI details.