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MERLIN LEGEND Communications System Release 6.1
Network Reference
555-661-150
Issue 1
August 1998
Introduction
Page 1-7Tandem Trunking and Tandem Switching
1
Figure 1–1. Series Configuration
To make a call from System A to System C, a user at Extension 4321 dials
3699 to
reach Extension 3699. The call travels over tandem trunks through System B to
System C without using the PSTN to provide switching services. Systems B and C
in this
series configuration
are called
tandem switches
.
Using another aspect of tandem switching, the user at Ext. 3699 employs
Automatic Route Selection (ARS) normally in order to dial a number in the New
York area code,
912125551234, for example, where 9 is the ARS code. In this case,
the call is routed from System C to System A over tandem trunks. At System A,
the call goes out over a facility connected to the PSTN as a local call from System
A.
These two calls have the following features in common:
■ All or part of each call is carried over tandem trunks.
■ The calls are routed seamlessly from a system extension to a destination.
■ The calls can result in substantial savings over the cost of the same calls
using telecommunications service providers and the PSTN.
■ The users dial the calls normally: one is an inside call and one is an ARS
call made on a System Access (SA) button. ARS and Universal Dial Plan
(UDP) routing are programmed to take advantage of all PSTN facilities in
the network.
Public Switched Telephone Network (PSTN)
Tie
PRI
PRI
New York, NY
Chicago, IL
Los Angeles, CA
Santa Monica, CA
ML A
ML B
ML C
ML D
Ext.
4321
Ext.
5455
Ext.
3699
Ext.
6233