Modern communications-based applications require a degree of flexibility, user control, responsiveness, and integrative capability beyond that provided in traditional networks. Solutions founded on digital connectivity implemented in a distributed processing environment have begun to meet these needs. These solutions have been constrained, however, by limits to the extent in which systems could communicate with each other across network boundaries. The Integrated Services Digital Network architecture defines key interfaces that support and extend this distributed processing capability and do this in an environment of internationally defined interface standards. These interfaces are channelized into two broad categories: information-bearing channels and signaling channels. Protocols for the latter have been defined using the layered architecture of the open systems interconnect reference model. Two specific ISDN access arrangements have been specified and are planned for systems within an overall ISDN architecture. Applications for such an architecture and future directions are discussed.