Chapter 4. Initial Configuration of Asterisk

Perseverance is the hard work you do after you get tired of doing the hard work you already did.

—Newt Gingrich

The purpose of this chapter is to guide the user through the configuration of four channels: a Foreign eXchange Office (FXO) channel, a Foreign eXchange Station (FXS) channel, a Session Initiation Protocol (SIP) channel, and an Inter-Asterisk eXchange protocol (IAX)[28] channel. The purpose is not to give an exhaustive survey of all channel types or topologies, but rather to provide a base platform on which to build your telecommunications system. Further scenarios and channel configuration details can be found in Appendix D. We start by exploring the basic configuration of analog interfaces such as FXS and FXO ports with the use of a Digium Dev-Lite kit . We’ll then configure two Voice over Internet Protocol (VoIP) interfaces: a local SIP channel connected to a soft phone, and a connection to Free World Dialup via IAX.

Once you’ve worked through this chapter, you will have a basic system consisting of many useful interfaces, and you will be ready to learn more about the extensions.conf file (discussed further in Chapter 5), which contains the instructions Asterisk needs to build the dialplan.

What Do I Really Need?

The asterisk character (*) is used as a wildcard in many different applications. It is the perfect name for this PBX for many reasons, one of which is the enormous number of interface types to which Asterisk can connect . These include:

  • Analog interfaces, such as your telephone line and analog telephones

  • Digital circuits, such as T-1 and E-1 lines

  • VoIP protocols such as SIP and IAX

Asterisk doesn’t need any specialized hardware—not even a sound card. Channel cards that connect Asterisk to analog phones or phone lines are available, but not essential. You can connect to Asterisk using the soft phones that are available for Windows, Linux, and other operating systems without using a special hardware interface. You can also use any IP phone that supports either SIP or IAX2. On the other side, if you don’t connect directly to an analog phone line from your central office, you can route your calls over the Internet to a telephony service provider.


[28] Officially, the current version is IAX2, but all support for IAX1 has been dropped, so whether you say “IAX” or “IAX2,” it is expected that you are talking about Version 2.

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