AT&T Information Systems Architecture defines a framework for compatibility among AT&T products as well as with key products of other vendors. A key direction of Information Systems Architecture is the use of standard, open interfaces and protocols. Standards now being defined for the Integrated Services Digital Network (ISDN) play an important role in the architecture. Support of ISDN will provide customers with uniform access to integrated voice and data capabilities which are provided through digital transmission and common channel signaling. Support of ISDN within Information Systems Architecture promises to provide customers with compatibility and high functionality. The AT&T Information Systems PBX product family already supports many capabilities that provide ISDN functionality. These capabilities make incorporation of ISDN in Information Systems Architecture and full support of ISDN a direct step in product evolution.

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Network design methods are described which determine the multiplexing and digital transmission facilities required to serve a given data‐circuit demand. The long‐haul network design is based on the definition of a three‐level network routing hierarchy, the derivation of intercity bit‐stream requirements, and a technique for selecting digital transmission facilities to carry the bit streams. The distribution network design within metropolitan areas makes use of different multiplexing combinations best suited to anticipated demands and techniques for using short‐haul digital facilities in an efficient manner.

This paper highlights AT&T's role in the evolution of ISDN switch‐to‐computer interfaces. Initially, the digital multiplexed interface (DMI) provided a multiplexed channel for data communications between a computer and a private branch exchange (PBX). DMI evolved to the Integrated Services Digital Network (ISDN) primary rate interface (PRI) that forms the backbone of many customers' networks. While PRI and DMI provided data transport applications based on higher performance, speed, and economy, these applications addressed only part of the potential power of an ISDN‐computer link. In telecommunications, the term “switch‐computer applications interface” (SCAI) is applied to linking computers and switches on an application (as opposed to a connectivity) basis. SCAI combines switches and computers in a client/server arrangement that provides new applications to integrate communications and computing functions. This paper describes the architecture, capabilities, and applications of AT&T's SCAI, the adjunct/switch application interface (ASAI). It addresses the requirements for marketing ASAI, specifically the need to conformance‐test ASAI interface implementations and test the interoperability of switch and computer applications. Finally, it identifies future trends for SCAI standards activities.