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COMMUNICATION SYSTEM NETWORKING — AN OVERVIEW 2-7
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• The Uniform Dial Plan function — With this function, the switch uses the extension number to find the
RNX. The RNX is used to route the call through AAR to its destination. The implementation of the
Uniform Dial Plan function here is identical to that used for the System 75 and Generic 1
communications systems when the UDP or PNA package is activated.
• Extension number portability (ENP) — With this dialing convention, the switch uses the extension
number to find a node number. The node number is then used to route the call through AAR to its
destination. Extension number portability is implemented so that terminals can be attached to any of a
number of switches in a cluster and still retain the same extension numbers. The cluster of switches is
called an ENP subnet. All switches in an ENP subnet share the same RNX number and must be either a
System 85 (R2V3 or R2V4) or a Generic 2 communications system.
Distributed Communications System
The distributed communications system (DCS) is 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.
Feature transparency is achieved by an information link over which the network nodes trade information
about a call. The DIMENSION, System 85, and DEFINITY Generic 2 communications systems use the data
communications interface unit (DCIU) to exchange this type of information between nodes. The System 75
and DEFINITY Generic 1 communications systems use the processor interface (PI) — sometimes called the
switch communications interface (SCI) — for information interchange.
Note: DCS is not provided when either DAC dialing or AAR feature-access-code dialing (8-RNX-XXXX)
is used.
NETWORK CALL PROCESSING
At the heart of networking software across all communications systems is the internal dial plan, and the
Automatic Route Selection (ARS) and Automatic Alternate Routing (AAR) features. Each of these
performs an essential function in the establishment of a network.
• The internal dial plan recognizes the type of call being made.
• AAR processes private network calls.
• ARS process public network calls.