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Chapter 4: Trunks 129
3. Trunk ( Prefix setting): If the trunk’s ANI has not been set, the system will
check to see whether a prefix has been set in the trunk. When this is the case,
the system will add the fixed number to the front of all calls leaving the trunk.
In many cases when you have an ITSP, you may want a prefix number to be
appended to the front of all calls. The prefix could be an account number, a
least-cost routing number, or a number to indicate an outside line on another
system (e.g., 9 as shown below).
4. Trunk ( Trunk ANI setting).
As a last resort, the system uses the DID number of the trunk, if there is one.
This is a typical scenario in the NANPA area, where a trunk has a primary num-
ber associated with it. When someone calls the number, the caller will typically
reach an auto attendant that processes the DID number.
Representing the Source
The system differentiates between the following two numbers when presenting a num-
ber on the trunk.
•
Display number: This number is the number that the user should see on the
display of the phone. In the case of a redirected call, this number would be the
original caller-ID that the system sees on the incoming call.
•
Network number: This number is the number that the provider wants to see
for billing purpose.