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COMMUNICATION SYSTEM NETWORKING — AN OVERVIEW 2-3
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SDN
ETN
LOCATION B
SATELLITE
MAIN
MAIN
MAIN
TANDEM
B
TANDEM
A
LOCATION A
• 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.