1. Overview

   In SIP-based media networks (RFC 3261prop [10]), there is a need to
   provide basic network media services.  Such services include playing
   announcements, initiating a media mixing session (conference), and
   prompting and collecting information with a user.

   These services are basic in nature, are few in number, and
   fundamentally have not changed in 25 years of enhanced telephony
   services.  Moreover, given their elemental nature, one would not
   expect them to change in the future.

   Multifunction media servers provide network media services to clients
   using server protocols such as SIP, often in conjunction with markup
   languages such as VoiceXML [20] and MSCML [21].  This document
   describes how to identify to a multifunction media server what sort
   of session the client is requesting, without modifying the SIP
   protocol.

   It is critically important to note that the mechanism described here
   in no way modifies the SIP protocol, the meaning, or definition of a
   SIP Request URI, or does it put any restrictions, in any way, on
   devices that do not implement this convention.

   Announcements are media played to the user.  Announcements can be
   static media files, media files generated in real-time, media streams
   generated in real-time, multimedia objects, or combinations of the
   above.

   Media mixing is the act of mixing different RTP streams, as described
   in RFC 3550std64 [13].  Note that the service described here suffices for
   simple mixing of media for a basic conferencing service.  This
   service does not address enhanced conferencing services, such as
   floor control, gain control, muting, subconferences, etc.  MSCML [21]
   addresses enhanced conferencing.  However, that is beyond the scope
   of this document.  Interested readers should read conferencing-
   framework [22] for details on the IETF SIP conferencing framework.

   Prompt and collect is where the server prompts the user for some
   information, as in an announcement, and then collects the user's
   response.  This can be a one-step interaction, for example by playing
   an announcement, "Please enter your pass code", followed by
   collecting a string of digits.  It can also be a more complex
   interaction, specified, for example, by VoiceXML [20] or MSCML [21].

1.1. Conventions Used in This Document

   RFC 2119 [6] the interpretations for the key words "MUST", "MUST
   NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT",
   "RECOMMENDED", "MAY", and "OPTIONAL" found in this document.