Page 365 - Asterisk™: The Future of Telephony

APPENDIX A

VoIP Channels

VoIP channels in Asterisk represent connections to the protocols they support. Each
protocol you wish to use requires a configuration file, containing general parameters
defining how your system handles the protocol as well as specific parameters for each
channel (or device) you will want to reference in your dialplan. In this appendix, we’ll
take an in-depth look at the IAX and SIP configuration files.

IAX

The IAX configuration file (iax.conf) contains all of the configuration information As-
terisk needs to create and manage IAX protocol channels. The sections in the file are
separated by headings, which are formed by a word framed in square brackets ([]). The
name in the brackets will be the name of the channel, with one notable exception: the
[general] section, which is not a channel, is the area where global protocol parameters
are defined.
This section examines the various general and channel-specific settings for iax.conf.
We will define each parameter and then give an example of its use. Certain options
may have several valid arguments. These arguments are listed beside the option, sep-
arated with the pipe symbol (|). For example, bandwidth=low|medium|high means that
the bandwidth option accepts one of the values low, medium, or high as its argument.
You can insert comments anywhere in the iax.conf file, by preceding the comment text
with the semicolon character (;). Everything to the right of the semicolon will be ig-
nored. Feel free to use comments liberally.

General IAX Settings

The first non-comment line in your iax.conf file must be the heading [general]. The
parameters in this section will apply to all connections using this protocol, unless de-
fined differently in a specific channel’s definition. Since some of these settings can be
defined on a per-channel basis, we have identified settings that are always global with
the tag “(global)” and those that can optionally be configured for individual channels

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