Call Control and Voice Apps: CCXML
Introduction and History
As editor of the new CCXML specification I am proud to report that the W3C has just released the first working draft of CCXML, a language to provide Call Control support for telephone applications.
What is Call Control?
Newton's Telecom Dictionary, 16th edition, defines Call Control as "the term used by the telephone industry to describe setting up, monitoring, and tearing down telephone calls". Fundamentally, Call Control is session control for telephone calls.
What is CCXML?
Traditionally, Call Control has required interaction with and understanding of telephony API's which often change from one platform to another.
CCXML is the "Call Control eXtensible Markup Language". It is an XML based language that can control the setup, monitoring, and tear down of phone calls. CCXML allows the industry to leverage the strength of web platforms and technologies to intelligently control calls on and off the telephone network. Additionally, CCXML will create a high-level industry standard for Call Control that can run over any telephony platform.
Why not build Call Control into VoiceXML directly?
VoiceXML was never designed to support advanced Call Control features -it was designed to be a dialog control language and it does that quite well. While VoiceXML does support basic Call Control features via the <transfer> tag, those features are in fact too basic for many telephony applications. Because of this limitation, vendors looked at adding Call Control to VoiceXML using several different approaches. Some companies added robust Call Control support by extending VoiceXML while others created their own Call Control languages such as CallXML from Voxeo or TXML from Telera. While these solutions provided enhanced Call Control support they were incompatible with each other and did not address all of the Call Control scenarios reviewed by the W3C.
VoiceXML controls the presentation of media inside of calls. It uses a model based on forms and transactions that occur in a linear fashion - a model that works very well for user driven voice interfaces. Call Control uses a model based on events and commands that can occur at any time. The fundamental differences in these models made it very difficult - if not impossible - to deliver robust Call Control inside of VoiceXML itself.
Additionally, many W3C members and telephone industry leaders wanted a language that could be used outside of VoiceXML itself. While only some phone calls require automated voice interaction, every phone call requires Call Control. As a result, CCXML could end up being used and supported by everything from PBX's to the telephone switches that run the phone network itself. Many of these telephony platforms have no need or support for the things VoiceXML itself can do.
What does CCXML allow you to do?
There are a number of features that VoiceXML currently can't supply that CCXML will:
- Support for multi-party conferencing, plus more advanced conference and audio control. Any telephone conferencing application requires such features.
- The ability to give each active line in a voice application its own dedicated VoiceXML interpreter. Currently, many VoiceXML platforms initiate a second call or "call leg" to transfer a call from an automated VoiceXML platform to another telephone user. The second leg of a transferred call on these platforms lacks a VoiceXML interpreter of its own, limiting the scope of possible applications that can occur on that second leg.
- Sophisticated multiple-call handling and control, including the ability to place outgoing calls at any time, initiated outside of the VoiceXML platform.
- Handling for richer and more asynchronous events. Advanced telephony operations involve substantial signaling, status events, and message-passing. VoiceXML does not currently have a way to integrate these asynchronous "external" events into its event-processing model.
- An ability to receive events and messages from systems outside of the CCXML or VoiceXML platform. Interaction with an outside call center platform, calls started asynchronously from the VoiceXML platform, and communication between multiple "clustered" VoiceXML or CCXML platforms all require event interaction from one platform to another.
CCXML allows developers to write advanced applications that require these features. Examples of such applications include
- "Follow me, Find me" applications that find the person you are trying to call by dialing their cell phone, home phone, and office phone in parallel.
- Call center applications that intelligently gather information from the caller and then pass that information on to the call center agent.
The W3C Voice Browser Working Group decided to tackle Call Control and came up with a set of comprehensive requirements that address the Call Control needs of almost all voice applications. After reviewing those requirements several proposals were submitted. CCXML is the result of those proposals.
CCXML is currently a first working draft and the specification is still far from complete. The W3C wanted to start getting comments from the public as early in the CCXML standardization process as possible. If you have comments on CCXML you can subscribe to the e-mail list and send in your feedback. You can sign up for the www-voice list by visiting http://www.w3.org/Voice .
What does CCXML do?
CCXML adds robust Call Control support to VoiceXML. However CCXML could also be used with other dialog systems such as a traditional IVR (Interactive Voice Response) platforms created before VoiceXML was available.
One critical thing to understand is that CCXML is not a media/dialog language like VoiceXML. It only provides support to move calls around and connect them to dialog resources. CCXML does not provide any dialog resources on its own. (Note: A dialog resource is anything that interacts with a caller via voice, such as a VoiceXML platform or even a second caller at another location.)
Continued...
back to the top
Copyright © 2001-2002 VoiceXML Forum. All rights reserved.
The VoiceXML Forum is a program of the
IEEE Industry Standards and Technology Organization (IEEE-ISTO).
|
