User guide

6.5 Configuration Files
The number of configuration files that you need to edit in order to run Asterisk depends on the types of
VoIP technologies that you want to use simultaneously in your actual installation. The basic logic behind
the configuration of Asterisk can be summarized in two steps:
Step 1: Define and Configure Communication Channels
First, you need to define and configure the communication channels that you want to use. A simple way
to picture a communication channel is a “phone wire.” The channels are the “logical wires” to your
PBX. As the Internet allows you to have several and simultaneous voice sessions running using the
same wire, you need to define each of those channels operating inside the tangible Internet wire.
Remember that Asterisk allows you to interconnect devices running different
VoIP protocols. This means that you can interconnect several types of IP (VoIP
phones, ATA, Softphones) and non-IP based telephony devices. The
configuration files that you need to prepare depend on the type of VoIP
technology to be used. Do not forget to install the samples files that can serve
as a guideline.
Step 2: Define Rules for Extensions (Create a dialplan)
Secondly, you need to describe the rules of how those channels will interact with each other. The voice
calls come to or leave your PBX via the previously defined channels, but those channels can interact
with each other in many different ways. For example, you might prefer that an incoming call from the
PSTN be forwarded automatically to a VoIP phone or, you might want to interconnect two IP phones in
a wireless network twenty kilometres apart. All that kind of “intelligence” between the channels is done
in a configuration file known as the extensions file. The extensions file contains all the rules known as a
dial plan.
To get a better picture of these VoIP concepts, think of the old telephony times when a person (the
operator) was responsible for connecting telephone wires manually. In order to place a call between
two telephone lines (the communication channels) it was necessary first to contact the operator (the
PBX) and then indicate who we wanted to call (extensions file). The channel configuration files
describes the type of telephone lines in use, and the extension configuration files replace the
functionality of the phone operator.
We will use these five basic configuration files in three different scenarios:
Configuration file Description
/etc/asterisk/extensions.conf Lays out the dialplan and brings channels together
Page 24 TRICALCAR | www.wilac.net/tricalcar – Version: February 2008