Asterisk has a lot of configuration files. Rather than assign all settings into one master configuration file; Asterisk opts to have many smaller files. This is advantageous since, depending on what hardware and features you are using, there are some files you may never touch. Another advantage is that a syntax error in one file may not necessarily bring down the entire system.

The dial plan is the keystone for the entire Asterisk system. Every phone call handled by Asterisk goes through the dial plan for routing information. Dial plans consist of three major parts: contexts, extensions, and variables. Contexts are groups of extensions that function together. Extensions are groups of commands that tell Asterisk what to do. Variables are simply used to store data. A special kind of context is a macro, which allows you to write small functions for common tasks in order to save code.

Two dial plan types are available: the common extensions.conf, and the newer more powerful extensions.ael. AEL stands for Asterisk Extension Language, which is a programming language developed by Digium for writing extensions. AEL is more powerful than the regular extensions.conf syntax, but is still very new and not fully mature.

Connections are the lifeblood of Asterisk. Without them you wouldn t be able to accomplish much since you wouldn t be able to talk to anyone. Asterisk supports numerous VoIP protocols and many models of hardware. The two most commonly used protocols in Asterisk are SIP and IAX2. SIP...