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Chapter 2 System telephony networking overview
Tandem calling to a remote PSTN
A system connected to a private network that uses dedicated circuits or VoIP circuits can allow a
user to dial directly to many other users, on different nodes, using a coordinating dialing plan.
Using a private network saves on toll charges, and local charges, as fewer PSTN accesses are
required for internal and external calling. Several nodes located on one site initiate their external
local calls to a centralized BCM having a T1 termination to the PSTN. This type of configuration
avoids multiple PSTN terminations at other local nodes.
The same tandeming concepts can be applied to inbound calls. DID numbers dialed from the
PSTN can be processed and tandem routed out of the centralized system to the localized remote
nodes. See other details on Tandem routing “Creating tandem private networks” on page 43.
Figure 3 Tandem dialing through a BCM to/from a private network
In the above example, there are three types of callers.
Each type of caller has a specific method of accessing the other two systems.
Callers using BCM
These callers can:
•
call directly to a specific telephone
•
select an outgoing line to access a private network
•
select an outgoing line to access features that are available on the private network
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