Asterisk Open-Source PBX System

The next file is voicemail.conf (Listing 3). Again, it has a general section that deals with general or global parameters for voice mail. The first parameter, format, lists the audio format of the messages. The next two parameters are used for e-mail notification: serveremail is the source e-mail address (from field), and attach instructs Asterisk to attach the message to the e-mail. In our example, we do not want the message attached. Again, some parameters have been omitted.

<mbox> is the number used to save and access messages for the user. This is also used in extensions.conf for directing the call flow to the proper voice-mail box. The <passwd> parameter is needed when checking messages. <name> is the name of the user. <email> and <pager> are e-mail addresses that are used to send message notifications. The pager e-mail has a shorter message, because it needs to be read on smaller devices (pagers and cell phones). Many mobile and pager providers have e-mail gateways that can deliver the message to the device.

The last file that we examine here is the extensions.conf file (Listing 4). This is one of the most involved files because it contains the dialplan. The dialplan in my example is rather simple compared to its capabilities. This file has a general and global section. The general section is similar to the general section in the previous files; it defines general parameters. I don't define any general parameters in this example. The global section is used to define global variables. These variables can be accessed in the dialplan by using the syntax ${VARIABLE}. I have defined one variable: TIMEOUT is the answer timeout. Built-in variables also can be used within the dialplan, such as, CONTEXT, EXTEN and CALLERID.

[globals]
TIMEOUT=12

[misc]
exten => t,1,PlayBack(timeout)
exten => t,2,Hangup()
exten => i,1,PlayBack(invalid)
exten => i,2,Hangup()

;  voicemail management
[voicemail]
include => misc
exten => 6245,1,VoiceMailMain2()
exten => 6245,2,Hangup

[iax]
include => misc
exten => 111/222,1,SetCIDName("it's your wife!")
exten => 111/222,2,agi(callerid.agi)
exten => 111/222,3,Dial(IAX/brett/s,${TIMEOUT})
exten => 111/222,4,Voicemail2(111)
exten => 111,1,agi(callerid.agi)
exten => 111,2,Dial(IAX/brett/s,${TIMEOUT})
exten => 111,3,Voicemail2(111)
exten => 222,1,Dial(IAX/maria/s,${TIMEOUT})
exten => 222,2,Voicemail2(222)
exten => maria,1,Goto(iax,222,1)
exten => 333,1,Dial(IAX/niko/s,${TIMEOUT})

[afterhours]
include => misc
exten => _.,1,Wait(1)
exten => _.,2,Answer
exten => _.,3,Background(vm-menu)

exten => 1,1,Voicemail2(111)
exten => 2,1,Voicemail2(222)
exten => 3,1,Voicemail2(333)

[cg1]
include => iax
include => voicemail

[cg2]
include => afterhours|1:00-6:00|*|*|*
include => iax

All of the other sections are context definitions. A context is simply a grouping of digit patterns. Here I have defined several contexts that define dialing scenarios: voicemail, iax and afterhours. Think of these as individual or mini-dialplans. I then define two contexts that I assign to the users. These inherit the capabilities of the other contexts I already have defined by using the include keyword.

The first context, voicemail, lists the digit patterns that allow users to access their voice-mail messages. Users can dial 6245, and the application VoicemailMain2 prompts them for the mailbox number and password. Users then can manage (listen to, delete and so on) the messages in their mailbox.

The iax context is used for PBX dialing between IAX users. We have defined various extensions for each of the users. An entry with the name of the user (maria) redirects to the extension number entry. For the 111 extension, I also match on callerid. If the callerid matches, I change the callerid name so it has a relative meaning. For example, if the extension dialed is 111, and the callerid is 222, the callerid name is changed to “it's your wife!”. This message shows up on my client whenever my wife calls me (I won't get into how I use this to my advantage).

The last digit pattern context is used for calls that arrive during late hours. Because I don't want to be disturbed at night by external users, I match on any dialed number (_.). It waits for one second and then answers the call. After it answers, it plays a background message so the caller can choose for which person to leave a message (“for brett, press 1”). So, if the caller presses 1, the call proceeds to the 1,1,Voicemail2(111) entry, which sends the user to the 111 mailbox. This is a simple illustration of how you could construct an IVR system.

The [cg1] and [cg2] contexts include functionality I already have defined inside other contexts. This allows me to create different user groups easily. For example, [cg1] has all of the capabilities I have defined, but [cg2] has only the iax capabilities and gets directed to voice mail during late hours. Powerful dialing capabilities can be constructed by utilizing the flexibility of Asterisk's dialplan. My example has shown only a glimpse of the possibilities. You also can simplify the dialplan by using macros, but I leave that as an exercise for the reader.