Page 147 - Asterisk™: The Future of Telephony

CHAPTER 5

Dialplan Basics

Everything should be made as simple as possible, but not
simpler.
—Albert Einstein (1879–1955)

The dialplan is truly the heart of any Asterisk system, as it defines how Asterisk handles
inbound and outbound calls. In a nutshell, it consists of a list of instructions or steps
that Asterisk will follow. Unlike traditional phone systems, Asterisk’s dialplan is fully
customizable. To successfully set up your own Asterisk system, you will need to un-
derstand the dialplan.
If you have attempted to read some sample dialplans and found them overwhelming,
or if you’ve tried to write an Asterisk dialplan and had no success, help is at hand. This
chapter explains how dialplans work in a step-by-step manner and teaches the skills
necessary to create your own. The examples have been designed to build upon one
another, so feel free to go back and reread a section if something doesn’t quite make
sense. Please also note that this chapter is by no means an exhaustive survey of all the
possible things dialplans can do; our aim is to cover just the fundamentals. We’ll cover
more advanced dialplan topics in later chapters.

Dialplan Syntax

The Asterisk dialplan is specified in the configuration file named extensions.conf.

The extensions.conf file usually resides in the /etc/asterisk/ directory, but
its location may vary depending on how you installed Asterisk. Other
common locations for this file include /usr/local/asterisk/etc/
and /opt/asterisk/etc/.

The dialplan is made up of four main concepts: contexts, extensions, priorities, and
applications. In the next few sections, we’ll cover each of these parts and explain how

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