Page 375 - Asterisk™: The Future of Telephony

Signaling and Payload Signaling and Payload Signaling and Payload
framing (converted) (voice) framing (converted) (voice) framing (converted) (voice)

Figure A-1. Trunking disabled
set transfer to no, the media path for this channel will always pass through Asterisk;
it cannot be redirected to another IAX node.
If you yourself are a remote node, and you need to connect into a remote node as a
user, you would define that main node as your peer:
[sashimi_platter]
type=peer
username=sushi
secret=wasabi
host=192.168.1.101
qualify=yes
trunk=yes
A peer is called from the dialplan by using Dial() with the name contained in square
brackets. If you need to authenticate to the peer with a username, you can set that
username and secret in the username and secret fields.

Remember, an incoming call from a user specified in iax.conf must au-
thenticate using the name specified in square brackets. When Asterisk
itself is calling to an outside peer however, you can use the username
setting to set the authentication username.

host is specified using either IP dotted notation or a fully qualified domain name
(FQDN). You can determine the latency between you and the remote host, and whether
the peer is alive, with qualify=yes. To minimize the amount of overhead for multiple
calls going to the same peer, you can trunk them.
Trunking is unique to IAX and is designed to take advantage of the fact that two large
sites may have multiple, simultaneous VoIP connections between them. IAX trunking
reduces overhead by loading the audio from several concurrent calls into each signaling
‡
packet. You can enable trunking for a channel with trunk=yes in iax.conf.
Figure A-1 shows a channel with trunking disabled, and Figure A-2 shows a channel
with trunking enabled.

Channel-specific parameters
Now, let’s take a look at the channel-specific parameters:

‡ You can think of IAX trunking as carpooling for VoIP packets. This becomes very useful in many situations,
as the IP overhead (UDP headers, IP headers, and so forth) is often bigger than the audio payload it carries.
If you have several concurrent calls between two Asterisk boxes, you definitely want to turn on IAX trunking!

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