MERLIN LEGEND Communications System Release 6.1
Feature Reference
555-661-110
Issue 1
August 1998
Features
Page 675Tandem Switching
A switch identifier should be unique across a network. This helps avoid a situation
called
automatic immediate cycling
. For example, when the switch identifiers for
the incoming trunks and the automatically selected outgoing trunks for a call
match indicating the tandem call would return to the originating switch, another
route for the call is selected if possible. However, if all available routes specify
systems with matching switch identifiers, the caller hears a fast-busy tone. The
call is routed to the destination system and then back to the originating system in
a continuous loop, until all available trunks are used.
Once switch identifiers are assigned, the system can be set up for proper routing
among networked systems. The next topic provides general descriptions of the
steps involved.
Automatic Route Selection (ARS), Uniform Dial
Plan Routing, and Remote Access 43
Tandem switching allows network system users to use ARS calls that are carried
on private network trunks to non-local systems where they are routed out over
public switched telephone network facilities. At the non-local systems to which or
through which calls are routed, the calls are received as remote-access calls,
even though the callers dial normally without using a remote access code. When
an ARS call arrives at a networked system, ARS routes the call cost-effectively
either over local lines/trunks accessing the public switched telephone network or
over tandem trunks that connect to another networked system.
For example, an organization might have a main office in Boston and subsidiary
offices in New Jersey and New York, connected by networked private tandem
trunks that link three MERLIN LEGEND Communications Systems. A user in the
New Jersey office who wishes to make an outside call to the 617 area code
(Boston) can do so through a line/trunk connected to the system in Boston. To
accomplish this, ARS routes the call from New Jersey over tandem trunks, first to
the New York system and then to the Boston system. Remote Access features are
used at the New York system, through which the call is routed, and at the Boston
system, where the outgoing call is sent to the public switched telephone network.
The caller does not dial a remote access code. For example, a user might dial,
.
This section discusses the general steps for setting up ARS and Remote Access
at the system where calls originate, at any intervening systems, and at the system
where the calls are connected to the public switched telephone network. It
includes the following two topics:
â– Local Calls Routed to Other Systems. This topic explains the factors that
you must consider when you set up your local system so that your users
can make ARS calls via public switched telephone network trunks
connected to another networked system.
System A
Origin (NJ)
System CSystem B
(Boston)
tandem
(NY)
tandem
PSTN
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