Ring communication system (Figure 1) using ISDN including terminal adapter hardware and associated software that can be combined with a general purpose computer and used to provide a work station or party unit which can be linked together with other similarly configured units via the ISDN to provide a closed wide area network. Although the system can be implemented on any type of computer using any programming language, in the preferred embodiment proprietary software designated WinISDN.DLL in a Microsoft Windows® environment is used to implement a novel algorithm in Visual Basic or C-language programming systems. The hardware aspects of the invention are provided in a terminal adapter card (Figure 2) that includes a dual port RAM, and ISDN controller, and a subscriber access controller. The adapter card plugs into the (E)ISA bus that is the PC standard bus/backplane.