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One of the more useful applications in an interactive Asterisk dialplan is the Back
ground()8 application. Like Playback(), it plays a recorded sound file. Unlike
Playback(), however, when the caller presses a key (or series of keys) on their tele‐
phone keypad, it interrupts the playback and passes the call to the extension that cor‐
responds with the pressed digit(s). If a caller presses 5, for example, Asterisk will stop
playing the sound prompt and send control of the call to the first priority of extension
5 (assuming there is an extension 5 to send the call to).
The most common use of the Background() application is to create basic voice
menus (often called auto attendants, IVRs,9 or phone trees). Many companies use
voice menus to direct callers to the proper extensions, thus relieving their reception‐
ists from having to answer every single call.
Background() has the same syntax as Playback():
[TestMenu]
exten => start,1,Answer()
same => n,Background(enter-ext-of-person)
If you want Asterisk to wait for input from the caller after the sound prompt has fin‐
ished playing, you can use WaitExten(). The WaitExten() application waits for the
caller to enter DTMF digits and is used directly following the Background() applica‐
tion, like this:
[TestMenu]
exten => start,1,Answer()
same => n,Background(enter-ext-of-person)
same => n,WaitExten()
8 It should be noted that some people expect that Background(), due to its name, will continue onward through
the next steps in the dialplan while the sound is being played. In reality, its name refers to the fact that it is
playing a sound in the background, while waiting for DTMF in the foreground.
9 More information about auto attendants and IVR can be found in Chapter 14.
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Chapter 6: Dialplan Basics
If you’d like the WaitExten() application to wait a specific number of seconds for a
response (instead of using the default timeout),10 simply pass the number of seconds
as the first argument to WaitExten(), like this:
same => n,WaitExten(5) ; We always pass a time argument to WaitExten()
Both Background() and WaitExten() allow the caller to enter DTMF digits. Asterisk
then attempts to find an extension in the current context that matches the digits that
the caller entered. If Asterisk finds a match, it will send the call to that extension. Let’s
demonstrate by adding a few lines to our dialplan example:
[TestMenu]
exten => start,1,Answer()
same => n,Background(enter-ext-of-person)
same => n,WaitExten(5)
exten => 1,1,Playback(digits/1)
exten => 2,1,Playback(digits/2)
After making these changes, save and reload your dialplan:
*CLI> dialplan reload
If you call into extension 201, you should hear a sound prompt that says, “Enter the
extension of the person you are trying to reach.” The system will then wait 5 seconds
for you to enter a digit. If the digit you press is either 1 or 2, Asterisk will match the
relevant extension, and read that digit back to you. Since we didn’t provide any fur‐
ther instructions, your call will then end. You’ll also find that if you enter a different
digit (such as 3), the dialplan will be unable to proceed.
Let’s embellish things a little. We’re going to use the Goto() application to have the
dialplan repeat the greeting after playing back the number:
[TestMenu]
exten => start,1,Answer()
same => n,Background(enter-ext-of-person)
same => n,WaitExten(5)
exten => 1,1,Playback(digits/1)
same => n,Goto(TestMenu,start,1)
exten => 2,1,Playback(digits/2)
same => n,Goto(TestMenu,start,1)
These new lines will send control of the call back to the start extension after playing
back the selected number.
10 See the dialplan function TIMEOUT() for information on how to change the default timeouts. See Chapter 10
for information on what dialplan functions are.
Building an Interactive Dialplan
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If you look up the details of the Goto() application, you’ll find that