Internet Engineering Task Force                                   SIP WG
Internet Draft                                     Rosenberg,Mataga,Ladd
draft-rosenberg-sip-vxml-00.txt                              dynamicsoft
July 13, 2001
Expires: February 2002


               A SIP Interface to VoiceXML Dialog Servers

STATUS OF THIS MEMO

   This document is an Internet-Draft and is in full conformance with
   all provisions of Section 10 of RFC2026.

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Abstract

   VoiceXML is an XML based scripting language for describing voice
   dialogs. VoiceXML interpreters run within an interpreter context
   that, among other tasks, provides a call control interface for
   accessing the interpreter. It is very natural to provide a VoIP-based
   interpreter context that uses SIP and RTP to communicate with the
   outside world. In this document, we provide detailed specifications
   for a SIP/RTP based interpreter context.


1 Introduction

   VoiceXML [1] is an XML based scripting language for describing voice
   dialogs. It supports user input through speech recognition and DTMF,
   and can communicate with the user through text-to-speech or recorded
   files. VoiceXML scripts are interpreted by a VoiceXML interpreter.



Rosenberg,Mataga,Ladd                                         [Page 1]

Internet Draft                  sip-vxml                   July 13, 2001


   This interpreter, in turn, runs within an interpreter context. The
   interpreter context is the interface between the outside world and
   the interpreter. It typically handles the mechanisms by which the
   script execution begins, and by which it is fed media to drive it. It
   also provides the means for fetching documents from some form of
   document server.

   It is very natural to provide a VoiceXML interpeter context based
   purely on IP. Specifically, based on VoIP using SIP [2] and RTP [3],
   along with HTTP for document access. An incoming VoIP call triggers
   the execution of the script, fetched from a server using HTTP. The
   incoming RTP stream for the call is passed to the interpeter for
   processing, and speech generated by the interpreter is sent over RTP
   to the called party. We call a pure IP-based VoiceXML system an "IP
   dialog server", or just "dialog server".

   Dialog servers are a key part of the application story for SIP-based
   networks, as described in the SIP application component architecture
   [4]. That document describes SIP-based dialog servers, and provides a
   high level overview of how the SIP interface works. This document
   provides a stand-alone, self-contained, more thorough description of
   a SIP-based VoIP VoiceXML interpreter context.

2 Script Initiation

   The script execution begins when a session is established using an
   INVITE request.

2.1 Script Naming

   In SIP, the request-URI identifies the user or service that the call
   is destined for. In the case of a dialog server, the dialog itself is
   the target for the call. As such, the request URI should contain the
   identifier for this dialog. This is consistent with the Request-URI
   service invocation model of RFC 3087 [5]. This URL can be in one of
   two formats. In the first, the VoiceXML script is identified directly
   by an HTTP URL. In the second, the script is not specified. Rather,
   the dialog server uses its configuration to map the incoming request
   to a specific script. The format for the Request-URI in either case
   is:



   Request-URI      =  "sip:" service-ID "." dialog-type ["." dialog-specific]
                       "@" hostport url-parameters [headers]
   service-ID       =  "dialog" | extension-token
   dialog-type      =  "vxml" | service-token
   dialog-specific  =  vxml-specific | service-token



Rosenberg,Mataga,Ladd