Regular Expressions (Regex)

You can configure SIP header manipulation rules using regular expressions (regex). Regex is a special text string pattern matching engine which is used to define the condition that must exist in order to use a specific manipulation rule. If the SIP header matches the regex pattern, then the "action" of the manipulation rule is applied to the SIP message. Executing a regex pattern also creates sub-expressions. The sub-expressions are referenced using the $n syntax, where n is a digit in the range of 1 to 13 (e.g., $3). Expressions enclosed by parenthesis (…) are stored in the variables $1, $2 … $n.

Note that spaces within a regular expression must be enclosed by parenthesis, as shown in the first example below:

body.sdp regex (AVP 8)
body.sdp regex avp

This feature provides the following main benefits:

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The device does not need to know the SIP header name or structure.

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The sub-expressions can be used in the manipulation action. All that is required is to set the action (for example, add, modify, etc.) and then reference the sub-expression you want to use as the value.

Regex is supported in the following tables and corresponding fields:

Configuration Tables and Relevant Fields

Table	Fields
Message Manipulations Table	■ 'Condition' ■ 'Action Value'
Message Conditions Table	■ 'Condition'
Pre-Parsing Manipulation Table	■ 'Pattern' ■ 'Replace-With'
Call Setup Rules Table	■ 'Condition' ■ 'Action Value'

Syntax:

<$n>

Where <$n> is used to reference a resulting sub-expression after executing a regex in a condition; where n is an integer referencing the sub-expression.