voicexml tutorial - post-dialing

VoiceXML 2.1 Development Guide

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Post-Dialing

Sometimes, we will want our application to be able to navigate directly through an office directory to connect with a particular callee's extension. We can use post-dialing in our VoiceXML transfer's to accomplish the keypresses, or DTMF input, necessary to do this.


<?xml version="1.0"?>
<vxml version="2.1">
  <form>
    <transfer name="MyCall" dest="tel:+12223334444;postd=ppp123" 
          bridge="true" connecttimeout="20s" maxtime="60s">
     <filled>
       <if cond="MyCall == 'busy'">
         <prompt>
           The lines are busy. Please try again later.
         </prompt>
         <exit/>
       </if> 
     </filled>
   </transfer>
 </form>
</vxml>

Note that the ‘p’ character indicates a pause between connection and post-dial input from the application; navigation of voicemail systems using the postdial method should be timed carefully using this syntax.

DTMF In-Band vs. Out-of-Band

What is the difference between in-band and out-of-band DTMF, and why does it matter? The simple explanation is, when you can hear the DTMF keypress over the phone's speaker, that is in-band DTMF - the audio tone is sent 'in-band' with the rest of the audio in the voice stream producing an audible beep. Out-of-band DTMF, or RFC2833, is when the DTMF signal is sent outside of the voice stream, producing no audible sound. Older PSTN or 'landline' phones use inband DTMF, while VoIP and digital phones, such as cell phones, send out-of-band DTMF. The use of out-of-band DTMF greatly reduces the likelihood of misrecognition or missed DTMF tones resulting in better DTMF recognition.

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CallerID and CalledID

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