AT&T 7200 series, 7500 series, 7100 series, 2500 series, 7400 series, 7300 series Network Evolution

COMMUNICATION SYSTEM NETWORKING — AN OVERVIEW 2-3

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LOCATION A

ETN

LOCATION B

MAIN

TANDEM

A

SDN

TANDEM

B

MAIN

MAIN

SATELLITE

∙Electronic tandem network/Software-Defined Network (ETN/SDN) hybrid network — A network in which users served by the public network are integrated into a private ETN. When users are scattered geographically, this may be a viable alternative to additional private network switches in dispersed locations, or public network toll calls from remote locations.

∙Distributed communications system (DCS) — An information system that provides a messaging overlay for ETN or main-satellite/tributary networks that are designed for DCS implementations. This overlay provides communication among the network nodes so that the operation of a limited number of features is transparent across the network.

∙Software-Defined Network (SDN) — SDN is a service provided by AT&T that allows users to build a complete or partial private network through the AT&T public network facilities.

NETWORK EVOLUTION

As a company grows and its networking needs change, its private network may evolve from a main-satellite network, to an ETN, and, finally, to an ETN/SDN hybrid arrangement. In addition, DCS may be installed when it is important for users across several switches to appear to be on the same switch. This may happen when there are communities of interest that span more than one location.