Filter
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7-19
Capture and Display Filters
Multi-State and Multi-Statement Filters
7
Filter Structure
The capture or display filter consists of states, each with a unique label so it can be
referenced. Each state contains an IF statement, an ELSE statement, and optional
ELSE IF statements. Each IF or ELSE IF statement is comprised of a condition to
match against packets and the actions to implement if the condition matches. The
ELSE statement is a set of actions to take when the other statements are false. The
actions result in the subset of data that is captured or displayed by Surveyor. The
statements and labels have an order, structure, and syntax. You always start and stay
in State0 until an action takes you to a different state.
Capture and display filters have the following structure:
ROOT statement (The root statement for capture filters con-
tains settings for global variables. The root statement for
display filters contains no variables.)
STATE0 identifier (Label for GoTo Action to Change the Fil-
ter
Operation -- Initial Starting Point)
IF statement (Specify conditions and actions)
ELSE IF statement (optional - same structure as IF statement)
other ELSE IF statements
ELSE statement (if no conditions satisfied, take these
actions)
STATE1 identifier (Label for GoTo Action to
Change the Filter Operation)
IF statement (Specify conditions and actions)
ELSE IF statement (optional - same structure as IF statement)
other ELSE IF statements
ELSE statement (if no conditions satisfied, take these
actions)
. ...
. ...
...
STATE3 identifier (Label for GoTo Action to
Change the Filter Operation)
IF statement (Specify conditions and actions)
ELSE IF statement (optional - same structure as IF statement)
other ELSE IF statements
ELSE statement (if no conditions satisfied, take these
actions)