Nortel BCM 3.7, Manual

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PRI networking using Call-by-Call services 519
Programming Operations Guide
PRI networking using Call-by-Call services
The example shown in the following figure highlights the use of PRI Call-by-Call services. It
shows two offices of a company, one in New York and one in Toronto. Each office is equipped
with a Business Communications Manager system and a PRI line. Each office has to handle
incoming and outgoing calls to the public network. In addition, employees at each office often
have to call colleagues in the other office.
Figure 182 PRI networking using Call-by Call Services
To reduce long distance costs, and to allow for a coordinated dialing plan between the offices,
private lines are used to handle interoffice traffic. Refer to
“Configuring the public and private
dialing plans” on page 312 .
If call-by-call services were not used, each Business Communications Manager system might have
to be equipped with the following trunks:
• 12 T1 DID lines needed to handle peak incoming call traffic.
• eight T1 E&M lines needed to handle inter-office calls.
• eight lines needed to handle outgoing public calls
The total required is thus 28 lines. If the Business Communications Manager systems were using
T1 trunks, then two T1 spans would be required at each office. Note that the total of 28 lines
represents the worst case value for line usage. In reality, the total number of lines in use at any one
time will generally be less than 28. For example, during periods of peak incoming call traffic, the
demand for outgoing lines will be low.
With PRI Call-by-call services, it is not necessary to configure a fixed allocation of trunks. Each of
the 23 lines on the PRI can be used for DID, private Tie, or outgoing public calls. This
consolidation means that it may be possible for each office to use a single PRI span, rather than
Network # 2221
Received # 2221
Internal # 2221
DID # 763-2221 Network # 6221
Received # 6221
Internal # 6221
DID # 562-6221
Toronto office
New York office
Tie Connection
Public Network
PRI PRI
Business Communications Manager
Central
Office
Central
Office