Number Expansion
Many larger offices use extension numbers to dial internally between users,
instead of the entire E.164 telephone number. Extensions can be defined as a
destination-pattern for a dial peer.This way the router will recognize the extension
number and will be able to translate it into the E.164 number; that is, if the
num-exp command has been implemented.
This will enable the router to prepend the digits you define before it passes
them to the remote telephony device.This will reduce the total number of digits
that must be dialed to complete a call to reach a user at a remote office location.
Number expansion is similar to implementing a prefix (discussed earlier), but
number expansion is applied to all dial peers, not just those defined.
An example of number expansion would be an office where you would dial
the last four digits of the E.164 address to reach someone within the company. In
this instance, the complete telephone number may be 747-3637, but internal
users would only have to dial 3637 to reach the particular user. All users located
at this office have the same first four digits (7473).With this information, you
cold configure the dial peers destination-patterns using each extension number,
and use number expansion to prepend those first four digits to the extension.The
router configurations would look like this:
num-exp 3… 7473…
dial peer voice 4 pots
destination pattern 3637
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