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Donald V. Glen

Abstract: There has been a significant internationa1 effort to develop standards for Integrated Services Digital Networks (ISDNs) at the same time that events leading to the divestiture of the American Telephone and Telegraph (AT&T) Company were occurring in the United States. The ISDN standards activity continues with end–to–end digital connectivity providing the basis for a myriad of new services for home and business as the objective. The divestiture has resulted in changed telephony markets and new network architectures for the Public Switched Telephone Network (PSTN). This report describes the PSTN operating structure as it existed prior to divestiture and as it now exists with new routing schemes, equal access principles, and Local Access Transport Areas (LATAs). Eight central office switches that are now, or have the potential to be, part of the new market and network structure in United States are also described. In essence, this report deals with the networks and switches that exist in the post–divestiture period and will become part of the anticipated ISDN era.

Keywords: circuit switching; Integrated Services Digital Network (ISDN); common channel signaling (CCS); access tandem; CCITT Signaling System No.7; central office switches; common channel interoffice signaling (CCIS); Dynamic Nonhierarchal Routing (DNHR); end office; equal access; Local Access Transport Area (LATA); local office; stored program controlled (SPC); tandem switch; public switched telephone network

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