asterisk/doc/extensions.txt

The Asterisk dialplan
=====================

The Asterisk dialplan is divided into contexts. A context is simply a group
of extensions. For each "line" that should be able to be called, an extension
must be added to a context. Then, you configure the calling "line" to have
access to this context.

If you change the dialplan, you can use the Asterisk CLI command
"extensions reload" to load the new dialplan without disrupting
service in your PBX.

Extensions are routed according to priority and may be based on any set
of characters (a-z), digits, #, and *. Please note that when matching a
pattern, "N", "X", and "Z" are interpreted as classes of digits.

For each extension, several actions may be listed and must be given a unique
priority. When each action completes, the call continunes at the next priority
(except for some modules which use explicitly GOTO's). 

When each action completes, it generally moves to the next priority (except for
some modules which use explicitly GOTO's. 

Extensions frequently have data they pass to the executing application
(most frequently a string).  You can see the available dialplan applications
by entering the "show applications" command in the CLI.

In this version of Asterisk, dialplan functions are added. These can
be used as arguments to any application. For a list of the installed
functions in your Asterisk, use the "show functions" command.

* Example dial plan

The example dial plan, in the configs/extensions.conf.sample file
is installed as extensions.conf if you run "make samples" after
installation of Asterisk. This file includes many more instructions
and examples than this file, so it's worthwile to read it.
	
* Special extensions

There are some extensions with important meanings:

	s:	What to do when an extension context is entered (unless
		overridden by the low level channel interface)
		This is used in macros, and some special cases. 
		"s" is not a generic catch-all wildcard extension.
	i:	What to do if an invalid extension is entered
	h:	The hangup extension, executed at hangup
	t: 	What to do if nothing is entered in the requisite amount
		of time.
	T:	This is the extension that is executed when the 'absolute'
		timeout is reached.  See "show function TIMEOUT" for more
		information on setting timeouts.	

And finally, the extension context "default" is used when either a) an 
extension context is deleted while an extension is in use, or b) a specific
starting extension handler has not been defined (unless overridden by the
low level channel interface).