System information

Your service provider will have a definition in either its sip.conf or iax.conf configuration
file (depending on whether you are connecting with the SIP or IAX protocol, respec-
tively) for your Asterisk server. If you only receive calls from this provider, you will
define it as a user (if it is another Asterisk system, you might be defined in its system
as a peer).
Now let’s say that your box is on your home Internet connection, with a dynamic IP
address. Your service provider has a static IP address (or perhaps a fully qualified do-
main name), which you place in your configuration file. Since you have a dynamic
address, your service provider specifies host=dynamic in its configuration file. In order
to know where to route your [phone] call, your service provider needs to know
where you are located in relation to the Internet. This is where the register statement
comes into use.
The register statement is a way of authenticating and telling your peer where you are.
In the [general] section of your configuration file, you place a statement similar to this:
register => username:secret@my_remote_peer
You can verify a successful registration with the use of the iax2 show registry and sip
show registry commands at the Asterisk console.
VoIP Security
We can barely scratch the surface of the complex matter of VoIP security in this ap-
pendix; therefore, before we dig in, we want to steer you in the direction of the VoIP
Security Alliance (http://www.voipsa.org). This fantastic resource contains an excellent
mailing list, white papers, howtos, and a general compendium of all matters relating
to VoIP security. Just as email has been abused by the selfish and criminal, so too will
voice. The fine folks at VoIPSA are doing what they can to ensure that we address these
challenges now, before they become an epidemic. In the realm of books on the subject,
we recommend the most excellent Hacking Exposed VoIP by David Endler and Mark
Collier (McGraw-Hill Osborne Media). If you are responsible for deploying any VoIP
system, you need to be aware of this stuff.
Spam over Internet Telephony (SPIT)
We don’t want to think about this, but we know it’s coming. The simple fact is that
there are people in this world who lack certain social skills, and that coupled with a
kind of mindless greed, means that these folks think nothing of flooding the Internet
with massive volumes of email. These same types of characters will think little of doing
the same with voice. We already know what it’s like to get inundated with telemarketing
calls; try to imagine what might happen when those telemarketers realize they can send
voice spam at almost no cost. Regulation has not stopped email spam, and it will prob-
ably not stop voice spam, so it will be up to us to prevent it.
636 | Appendix B: Protocols for VoIP
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