Digit Stripping
Digit stripping strips any outbound digits that explicitly match the destination pattern of
a particular dial peer. By default, POTS dial peers strip any outbound digits that explicitly
match their destination pattern, whereas VoIP dial peers transmit all digits in the called
number. For example, given a destination pattern of 5551... the number transmitted to
the PSTN would contain the last three digits. The first four digits, 5551, would be
stripped because they explicitly match the destination pattern.
In Figure 7-2, users dial a 9 to reach an outside number. If the configured destination pattern
is 9T, the 9 is matched and stripped from the called number sent to the PSTN. On
the other hand, you might have a dial peer for an emergency number such as 911 in the
United States If the destination pattern is 911, you would not want the numbers stripped
when they are explicitly matched. In this case you could use the no digit-strip command
to disable the automatic digit-stripping function. This allows the router to match digits
and pass them to the telephony interface. Figure 7-2 shows an example of this behavior.
372 Authorized Self-Study Guide Cisco Voice over IP (CVOICE)
dial-peer voice 9 pots
destination-pattern 9T
dial-peer voice 911 pots
destination-pattern 911
Dialed Number:
9 281 555-1234
Transmitted Number:
281 555-1234
Dialed Number:
911
Transmitted Number:
None!
dial-peer voice 911 pots
destination-pattern 911
no digit-strip
Dialed Number:
911
Transmitted Number:
911
Reorder
Tone
V
PSTN
Figure 7-2 Digit Stripping Example