AT&T ISDN Service Operations and Test Plan for Phase 1-Issue 2.

The AT&T Integrated Services Digital Network (ISDN) provides a flexible digital access service between the customer location and the AT&T Service Node. The architecture consists of a digital PBX interface (or other Customer Premise Equipment (CPE) supporting the Primary Rate Interface (PRI), DS1 digital transport to the Service Node, an Integrated Access Distributor (IAD) Digital Access and Cross Connect System (DACS) to integrate private line and switched services on one access line and the 4ESS(TM) switch (including the Common Network Interface (CNI) ring). Phase 1 ISDN introduces D channel out-of-band signaling which allows 64 Kbps channel and other feature capabilities.