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602 Chapter 16: Voice Techniques
·
Toll call control
·
Least-cost routing
Whenever you use a phone in an office situation, it is very likely that a dial plan governs the
flow of voice traffic. The internal extensions are mapped to direct in-house numbers. Interoffice
calls typically require you to enter four digits to reach an extension. The plan might require you
to dial 9 to get access to the outside network. It might require dialing 8 to get access to long-
distance calls. The plan might require access codes to make long-distance calls. Some phones
might not be able to access the outside network. Dial plans typically create a number of Class
of Service (CoS)
groups. CoS assigns privileges to users. A class can contain one or many users.
CoS can also restrict access during specified times.
To describe a typical dial plan, let's take a look at a small voice network with four remote sites
and a central site. Users at all sites can dial three-digit extensions to reach other users at the local
site. To call between sites, the users must use a trunk access code to connect the phone switch
to the remote site. After receiving a second dial tone, users can dial a three-digit extension. In
this example, users from Site A must dial 2 to reach site B, 3 to reach site C, and 4 to reach site
D. Table 16-3 depicts the dial plan for a small network. The dial plan allows for scalability up
to 1000 connections.
Table 16-3
Network Dial Plan
Source
Destination
Dialed Numbers
From Site 1
To Site 1
001­999
From Site 1
To Site 2
2001­2999
From Site 1
To Site 3
3001­3999
From Site 1
To Site 4
4001­4999
From Site 2
To Site 2
001­999
From Site 2
To Site 1
1001­1999
From Site 2
To Site 3
3001­3999
From Site 2
To Site 4
4001­4999
From Site 3
To Site 3
001­999
From Site 3
To Site 1
1001­3999
From Site 3
To Site 2
2001­3999
From Site 3
To Site 4
4001­4999
From Site 4
To Site 4
001­999
From Site 4
To Site 1
1001­1999
From Site 4
To Site 2
2001­2999
From Site 4
To Site 3
3001­3999
87200333.book Page 602 Wednesday, August 22, 2001 1:41 PM