Asterisk: The Definitive Guide, 5th Edition

Chapter 6. Dialplan Basics

Everything should be made as simple as possible, but not simpler.

Albert Einstein

The dialplan is the heart of your Asterisk system. It defines how calls flow into and out of the system. The dialplan is written in a scripting language, which specifies instructions that Asterisk follows in response to calls arriving from channels. In contrast to traditional phone systems, Asterisk’s dialplan is fully customizable.

Experienced software developers find Asterisk dialplan code archaic, and often prefer to control call flow using Asterisk APIs such as AMI and ARI (which we will discuss in later chapters). Regardless of your plans in this regard, learning how Asterisk behaves is far easier if you understand dialplan first. It is perhaps also worth noting that Asterisk dialplan is performance-tuned, and is therefore the fastest way to execute call flow in terms of responsiveness and minimal load on the system. Dialplan is fast.

This chapter introduces the essential concepts of the dialplan, which will form the basis of any dialplan you write. Do not skip too much of this chapter, since the examples build on each other, and it is so fundamentally important to Asterisk. 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 essentials. We’ll cover more advanced dialplan topics in later chapters. You are encouraged to experiment.

Dialplan Syntax

The Asterisk dialplan is specified ...