System information

One of the more unique features of the IAX protocol is IAX trunking.
Trunking an IAX connection could be useful on any network link that will often be
carrying multiple simultaneous VoIP calls between two systems. By encapsulating mul-
tiple audio streams in one packet, IAX trunking cuts down on the overhead on the data
connection, which can save bandwidth on a heavily used network link.
The principal advantage of IAX encryption is that it requires one simple
change to the /etc/asterisk/iax.conf file:
[general]
encryption = yes
For extra protection, you can set the following option to ensure that no IAX connection
can happen without encryption:
forceencryption = yes
Both of these options can be specified in the [general] section, as well as in peer/user/
friend sections in iax.conf.
Emergency Dialing
In North America, people are used to being able to dial 911 in order to reach emergency
services. Outside of North America, well-known emergency numbers are 112 and
999. If you make your Asterisk system available to people, you are obligated (in many
cases regulated) to ensure that calls can be made to emergency services from any tele-
phone connected to the system (even those phones that otherwise are restricted from
making calls).
One of the essential pieces of information the emergency response organization needs
to know is where the emergency is (i.e., where to send the fire trucks). In a traditional
PSTN trunk this information is already known by the carrier and is subsequently passed
along to the Public Safety Answering Point (PSAP). With VoIP circuits things can get
a bit more complicated, by virtue of the fact that VoIP circuits are not physically tied
to any geographical location.
You need to ensure that your system will properly handle 911 calls from any phone
connected to it, and you need to communicate what is available to your users. As an
example, if you allow users to register to the system from softphones on their laptops,
what happens if they are in a hotel room in another country, and they dial 911?
†
The dialplan for handling emergency calls does not need to be complicated. In fact, it’s
far better to keep it simple. People are often tempted to implement all sorts of fancy
functionality in the emergency services portions of their dialplans, but if a bug in one
of your fancy features causes an emergency call to fail, lives could be at risk. This is no
IAX trunking.
IAX encryption.
† Don’t assume this can’t happen. When somebody calls 911 it’s because they have an emergency, and it’s not
safe to assume that they’re going to be in a rational state of mind.
154 | Chapter 7: Outside Connectivity