Page 148 - Asterisk™: The Future of Telephony

they work together. After explaining the role each of these elements plays in the
dialplan, we will step you though the process of creating a basic, functioning dialplan.

Sample Configuration Files
If you installed the sample configuration files when you installed Asterisk, you will most
likely have an existing extensions.conf file. Instead of starting with the sample file, we
suggest that you build your extensions.conf file from scratch. This will be very beneficial,
as it will give you a better understanding of dialplan concepts and fundamentals.
That being said, the sample extensions.conf file remains a fantastic resource, full of
examples and ideas that you can use after you’ve learned the basic concepts. We suggest
you rename the sample file to something like extensions.conf.sample. That way, you
can refer to it in the future. You can also find the sample configuration files in
the /configs/ directory of the Asterisk source.

Contexts

Dialplans are broken into sections called contexts. Contexts are named groups of ex-
tensions, which serve several purposes.

Contexts keep different parts of the dialplan from interacting with one another. An
extension that is defined in one context is completely isolated from extensions in any
other context, unless interaction is specifically allowed. (We’ll cover how to allow in-
teraction between contexts near the end of the chapter.)
As a simple example, let’s imagine we have two companies sharing an Asterisk server.
If we place each company’s voice menu in its own context, they are effectively separated
from each other. This allows us to independently define what happens when, say, ex-
tension 0 is dialed: people pressing 0 at Company A’s voice menu will get Company
A’s receptionist, and callers pressing 0 at Company B’s voice menu will get Company
B’s receptionist. (This example assumes, of course, that we’ve told Asterisk to transfer
the calls to the receptionists when callers press 0.)

Contexts are denoted by placing the name of the context inside square brackets ([ ]).
The name can be made up of the letters A through Z (upper- and lowercase), the num-
*
bers 0 through 9, and the hyphen and underscore. For example, a context for incoming
calls looks like this:
[incoming]

* Please note that the space is conspicuously absent from the list of allowed characters. Don’t use spaces in
your context names—you won’t like the result!

120 | Chapter 5: Dialplan Basics