VoiceXML Review - Columns - Speak & Listen

In this monthly column, an industry expert will answer common questions about VoiceXML and related technologies. Readers are encouraged to submit questions about VoiceXML, including development, voice-user interface design, and speech technology in general, or how VoiceXML is being used commercially in the marketplace. If you have a question about VoiceXML, e-mail it to and be sure to read future issues of VoiceXML Review for the answer.

Q: Hi, I would like to ask is it possible for me to get the caller ID (i.e. the phone number which the user called from)? Please help.

A: The caller ID information can be accessed through the VoiceXML session variable session.telephone.ani -IF- it is provided by the telephony interface. Also, if you are using analog telephone lines, you would need to ensure that your service provider is providing the caller ID (also known as the ANI - automatic number identification) on the line. An example of VoiceXML code that retrieves the caller Id info would look something like the following:

<?xml version="1.0"?>

<vxml version="1.0">
  <var name="phoneNumber" />
  <script>
    phoneNumber = session.telephone.ani;
  </script>
  <form id="sayNumber">
    <block>
      Your phone number is <value expr="phoneNumber"/>
    </block>
  </form>
</vxml>

A: There is no predefined VoiceXML variable that will return the duration of a phone call. However, you can calculate this on your own with some simple ECMAScript and event handling. Let's look at an example:

<?xml version="1.0"?>

<vxml version="1.0">
  <var name="startDate" />
  <var name="startTime" />
  <script>
  startDate = new Date();
  startTime = startDate.getTime();
  </script>
  <catch event="telephone.disconnect.hangup">
    <script>
      var endDate = new Date();
      var endTime = endDate.getTime();
      var callDuration = endTime - startTime;
    </script>
      <submit next = "http://someURL/logTime.jsp"
              namelist = "callDuration"
              method = "get" />
  </catch>
  <form id="sayGoodbye">
    <block name="block1">You can hangup now.
      <throw event="telephone.disconnect.hangup" />
    </block>
  </form>
</vxml>

In this example, the initial <script> executes upon loading the document into the VoiceXML interpreter. An ECMAScript Date object is instantiated as startDate and the starting time is determined through the getTime() method of this object (for those unfamiliar with ECMAScript or JavaScript, I recommend paging through one of the many excellent books currently available on the topic). Finally, when the caller hangs up a telephone.disconnect.hangup event is thrown. This event is caught with application scope by the <catch event = "telephone.disconnect.hangup"> tag and all handling is performed by the enclosed code. This includes a <script> that gets the time at which the event was thrown by instantiating a new Date object endDate, and calculating the call duration (the difference between the starting and finishing times). It should be noted that all return values of the getTime() method are in msec. Hence, the value of the callDuration variable will also be in msec. After determining the call duration, the application sends the value to a server page called "logTime.jsp" for processing via the <submit> tag.

Note that if an application spans two or more VoiceXML documents, it would be necessary to declare and initialize the startTime variable in the application root document.

Answers to Your Questions About VoiceXML

By Eric Tober

Q: Hi, I would like to ask is it possible for me to get the caller ID (i.e. the phone number which the user called from)? Please help.