4.7. Configuring Inbound IAX
Connections
The Inter-Asterisk eXchange (IAX) protocol is
usually used for server-to-server communication; more hard phones
are available that talk SIP. However, there are several soft phones
that support the IAX protocol, and work is progressing on several
fronts for hard phone support in firmware. The primary difference
between the IAX and SIP protocols is the way media (your voice) is
passed between endpoints.
With SIP, the RTP (media) traffic is passed
using different ports than those used by the signaling methods. For
example, Asterisk receives the signaling of SIP on port 5060 and
the RTP (media) traffic on ports 10,000 through 20,000, by default.
The IAX protocol differs in that both the signaling and media
traffic are passed via a single port: 4569. An advantage to this
approach is that the IAX protocol tends to be better suited to
topologies involving NAT.
An IAX user is
used to authenticate and handle calls coming into the PBX system.
For calls going out from the PBX, Asterisk uses an IAX
peer entry in the iax.conf file to authenticate with the remote
end. (IAX peers will be explored in the section "Configuring
Outbound IAX Connections.")
This section explores the configuration of your
system for a Free World Dialup (FWD) account via IAX. Free World
Dialup is a free VoIP service provider that allows you to connect
to any other member of the network, regardless of physical
location, for free. FWD is also connected to over 100 other
networks to which you can connect for free.
This section sets up iax.conf and extensions.conf to allow you to accept calls
from another FWD user. The section on outgoing IAX
connections deals with placing
calls.
4.7.1. iax.conf Configuration
In iax.conf,
sections are defined with a name enclosed in square brackets
([]). Every iax.conf file
needs at least one main section: [general]. Within the
[general] section, you define the settings related to the
use of the IAX protocol, such as default codecs and jitter
buffering. You can override the default codecs you specify in the
[general] section by specifying them within the
user or peer definitions.
The following [general] section is the
default from the iax.conf.sample
configuration file (the same file that's installed when you perform
a make samples). For more information about the options,
see Appendix A.
[general]
bandwidth=low
disallow=lpc10
jitterbuffer=no
forcejitterbuffer=no
tos=lowdelay
autokill=yes
register => fwd_number:password@iax2.fwdnet.net
[iaxfwd]
type=user
context=incoming
auth=rsa
inkeys=freeworlddialup
Within the [general] section, you'll
need to add a register statement. The purpose of the
register statement is to tell the FWD IAX server where you
are on the Internet (your IP address). When a call is placed to
your FWD number, the FWD servers do a lookup in their database and
forward the call to the IP address associated with the FWD
number.
In the [iaxfwd] section, define the
user for incoming calls with type=user. Then define where
the incoming call will be handled within the dialplan , with context=incoming. To specify
that the authentication for the incoming call will be done with an
RSA public/private key pair, use auth=rsa. The public key
is defined with inkeys=freeworlddialup. The
freeworlddialup public key comes standard with
Asterisk.
4.7.2. Dialplan Configuration
Handling an incoming call in the extensions.conf file is simple. First, create
a context called incoming (the same context name
configured for the iaxfwd user in iax.conf). The context is followed by a
Dial( ) statement that will dial the SIP extension created
earlier in this chapter. Replace the number 10001 with
that of your FWD account:
[incoming]
exten => 10001,1,Dial(SIP/john)
|
