Asterisk: The Future of Telephony, 2nd Edition

Connecting Two Asterisk Boxes Together via IAX

Often it is desirable to connect two physical Asterisk boxes together via IAX in order to send calls between two physical locations (the distance between these locations may be centimeters or kilometers). One of the advantages to using the IAX protocol to do this is a feature called trunking, which utilizes a method of sending the voice data for multiple calls at once with a single header. This has little effect on only one or two simultaneous calls, but if you are sending tens or hundreds of calls between two locations, the bandwidth savings by utilizing trunking can be tremendous.

Configuring a Local Firewall

If you’re running iptables on the same machine as the Asterisk box, then you can run the following commands to open port 4569 for the IAX2 protocol. An excellent book on iptables firewalls is Linux Firewalls by Steve Suehring and Robert Ziegler (Novell Press).

# iptables -I RH-Firewall-1-INPUT -p udp --dport 4569 -j ACCEPT
#service iptables save

Be aware that this will allow all UDP traffic from any source access to port 4569.

Note

You will need a timing interface installed on your system, whether it be hardware from Digium or via the kernel by using the ztdummy driver. This will require you to have Zaptel installed on your system and running. See Chapter 3 for more information about installing Zaptel.

Configuring Our Asterisk Boxes

We’ll be utilizing a simple topology where we have two Asterisk boxes registered to each other directly, ...