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Figure 619 Flow chart for dial plan operation process on the called side
1. After receiving a voice call (the called number), the voice gateway on the called side performs
global calling/called number substitution.
2. The voice gateway on the called side selects proper local numbers or call routes based on the
local number or call route selection priority rules. Number substitution might also be involved
during the local number or call route selection. If the called party is a local number, the gateway
directly connects the line. If the called party is a PSTN subscriber, the gateway initiates a call
and sends the calling and called numbers to the PSTN. The PBX in the PSTN connects the call.
Regular expression
You will use some regular expressions frequently when you configure number substitution rules.
Regular expressions are a powerful and flexible tool for pattern matching and substitution. They are
not restricted to a language or system, and have been widely accepted.
When using a regular expression, you must construct a matching pattern according to certain rules,
and then compare the matching pattern with the target object. The simplest regular expressions do
not contain any meta-character. For example, you can specify a regular expression hello, which only
matches the string hello.
To help you construct matching patterns flexibly, regular expressions support some special
characters, called meta-characters, which define the way other characters appear in the target
object.
Table 231 Meta-characters
Meta-character Meaning
0-9 Digits 0 through 9.
# and * Each indicates a valid digit.
.
Wildcard, which can match any valid digit. For example, 555…. can match any number
beginning with 555 and ending in four additional characters.
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