Category Archives: Asterisk

First Release of PHP Swift TTS Extension

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I’m happy to announce the first release of the Swift Text-To-Speech PHP extension; the swift engine is the free TTS engine provided with any Cepstral TTS voice. A lot of Asterisk fans out there will recognize the Cepstral Allison voice, as the default voice for Asterisk installations.

The extension will only work on systems support by the Swift engine, and has only been tested (so far) on Linux (CentOS).

The extension will generate audio based on the text provided, and can be exported in several different audio formats, including:

  • PCM (RAW audio)
  • u-law / a-law (logarithmically encoded RAW audio)
  • WAV (RAW audio)
  • GSM (when compiled with the libgsm library)
  • MP3 (when compiled with the libmp3lame library)

A simple example on how to use this:

//
// create the new TTS object
//
$tts = new SwiftTTS();

//
// set a voice to use for generation
//
$tts->setVoice("Allison");

//
// generate text, and return a stream for the audio
//
$s = $tts->generate("hello my name is allison", SwiftTTS::FORMAT_WAV);
if ($s !== false)
{
        //
        // write the stream contents to a file
        //
        file_put_contents("audio.wav", $s);
}

For more details, and to download the current version, see the Google Code page.

Automatic Dial Resource Fail-over in Asterisk

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Asterisk is generally pretty reliable, but termination providers aren’t always so good; in a market where anybody can re-sell an upstream provider, or setup a few Asterisk boxes and start routing calls for people, it’s generally a good idea to have a “backup” provider (or three) to route your calls through.

You can easily setup an Asterisk system, to fail-over to secondary systems, if your primary provider fails for some reason- and this can all be done right in the dial plan, using a simple MACRO.

Add this MACRO to your dial plan:

[macro-direct-dial]
exten => s,1,Set(CALL_ATTEMPT=1)
exten => s,2,Set(TERM_PROVIDER=${TERM_PROVIDER1})
exten => s,3,Dial(${TERM_PROVIDER}/${ARG1},60)
exten => s,4,GotoIf($["${CALL_ATTEMPT}" >= "${MAX_PROVIDERS}"]?s-CANCEL,1)
exten => s,5,Set(CALL_ATTEMPT=$[${CALL_ATTEMPT} + 1])
exten => s,6,Goto(s-${DIALSTATUS},1)

exten => s-BUSY,1,Noop()
exten => s-NOANSWER,1,Noop()
exten => s-CANCEL,1,Hangup()
exten => s-HANGUP,1,Hangup()

exten => s-CHANUNAVAIL,1,Set(TERM_PROVIDER=${EVAL(${TERM_PROVIDER${CALL_ATTEMPT}})})
exten => s-CHANUNAVAIL,2,Goto(s,3)

exten => s-CONGESTION,1,Set(TERM_PROVIDER=${EVAL(${TERM_PROVIDER${CALL_ATTEMPT}})})
exten => s-CONGESTION,2,Goto(s,3)

Now you’ll need to route your calls into this MACRO; this can vary by dial plan, as you may have a special configuration for different area codes, or country codes, or based on some least-cost-routing business decisions, but a simple example would be something like this:

[default]
exten => _1NXXNXXXXXX,1,Answer()
exten => _1NXXNXXXXXX,2,Macro(direct-dial,${EXTEN})
exten => _1NXXNXXXXXX,3,Hangup()

This routes any NANPA numbers through the direct-dial MACRO above, passing in the phone number as the first argument to the MACRO.

Now, before this will work, you’ll need to configure some variables; this can be done in many places- in my working configuration, I have these variables dynamically generated via an AGI script, based on the phone number being dialed. This way I can control dial-groups, by phone number, based on a cost/preference/etc.

In this example, we’ll simply set these values in the globals section of the extensions.conf file:

[globals]
TERM_PROVIDER1 = SIP/first_provider
TERM_PROVIDER2 = IAX/second_provider
TERM_PROVIDER3 = SIP/last_provider
MAX_PROVIDERS = 3

So I’ve configured three fictitious termination providers; you can specify as many as you like, as long as the TERM_PROVIDER increments one for each, and you set the MAX_PROVIDERS value to the total number of providers listed.

This is obviously more useful if this list is automatically generated somehow, or changed based on the phone number being dialed, otherwise the retries could simply be hard-coded into the dial plan.

Now when you dial your number, it will start with the first (default) provider; if the dial() function returns a congestion or channel un-available error, the MACRO will cycle to the next provider, until it as gone through all of the providers listed.