[Telecom] Anyone remember how a Teloquent ACD system talks to VSM???

I've got an old teloquent ACD (auto call dist.) system. (version

The system uses ISDN, and analog phone lines connected to BRI cards (ISA).

The system has 2 main components: Phone Server: runs on SCO unix OSR5 VSM (voice service module): runs on dos 6.2

A call comes in, and appears to both boxes, and the phone server tells the VSM which line to answer, and what message to play.

The phone server controls the VSM via an ISDN phone line.

My question is this: Can anyone tell me how this communication takes place, what protocol it uses, and the best way to diagnose why this communication is not happening? ( Or anything more than what I've described ??)

OR Can anyone point me to where there's DETAILED documentation?

appreciate any help! TIA Bob