Answers to Your Questions About VoiceXML
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.
This month we examine more questions from our readers.
Q: After the caller has hung up, is there any way for me to perform any "clean up" to track that back on my Web server?
A: Yes. There are several reasons why VoiceXML developers often want to perform some kind of "post-hangup processing". Most often, it is to POST some final information back to the Web server for logging/tracking purposes. For example, a commerce application may want to explicitly note the list of things that were left in a caller's shopping cart when they suddenly hung up without buying anything.
VoiceXML specifies the pre-defined events "telephone.disconnect.hangup" and "telephone.disconnect.transfer", which can be caught to do this kind of post-hangup processing. "telephone.disconnect.hangup" is thrown when the caller explicitly hangs up the phone, and "telephone.disconnect.transfer" is thrown when a blind (non-bridging) call transfer is invoked and the caller has been permanently transferred to another line and will not return.
A simple example of using "telephone.disconnect.hangup" to submit information back to your Web server is as follows:
<!-- APPLICATION_ROOT.VXML -->
<vxml>
<!-- some global variables -->
<var name="last_state" expr="'null'" />
<var name="usr_id" expr="'null'" />
<!--this defines an application-scope event handler for post-hangup
processing -->
<catch event="telephone.disconnect.hangup">
<submit namelist="last_state usr_id" src="onhangup.jsp"
fetchtimeout="5s" />
</catch>
</vxml>
<!-- MY_APPLICATION.VXML -->
<vxml application="application_root.vxml">
...
...
<!-- your whole application that sets last_state and usr_id
throughout -->
...
...
</vxml>
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Note that in the global event handler above, "fetchtimeout" is limited to 5 seconds. This is intentiona -- it's important to note that post hangup processing can be very tricky performance-wise. It could be very easy to write applications that accidentally (or intentionally) take a long time to complete this processing, and would ultimately crash or seriously degrade the performance of your VoiceXML server once enough calls had passed through the system. It's critical to evaluate both your VoiceXML platform and your application's performance and design with regard to this feature.
Q: Does VoiceXML support cookies?
A: Because VoiceXML is based on HTTP and the Web development paradigm, it is natural to assume that VoiceXML should support cookies just like "regular" Web sites. Technically, the VoiceXML 1.0 specification does not explicitly include or preclude support for cookies. However, most commercial VoiceXML platform implementations available today do support "session cookies"; cookies which expire at the end of a "browser session", which in the case of VoiceXML is a single phone call. Most platform implementations do not support "persistent" cookies, because on the phone they require the notion of a persistent user database with formalized authentication for callers. This is because, on the phone, your browser is "in the cloud" so to speak and the only way for the system to get *your* persistent cookies securely would be for you to explicitly sign in with a user name and password or equivalent authentication mechanism. Automatic Number Identification (ANI) or Caller ID cannot be used for this, because they are not guaranteed to map to a specific user of a specific telephone handset.
Several of the online VoiceXML development resources called out on http://www.voicexml.org/faqs.html have detailed information and code examples on how to use cookies with VoiceXML applications.
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