Network Working Group                                         E. Candell
Request for Comments: 3773                                      Comverse
Category: Informational                                        June 2004


            High-Level Requirements for Internet Voice Mail

Status of this Memo

   This memo provides information for the Internet community.  It does
   not specify an Internet standard of any kind.  Distribution of this
   memo is unlimited.

Copyright Notice

   Copyright (C) The Internet Society (2004).

Abstract

   This document describes the high-level requirements for Internet
   Voice Mail (IVM) and establishes a baseline of desired functionality
   against which proposed MIME profiles for Internet Voice Messaging can
   be judged.  IVM is an extension of the Voice Profile for Internet
   Mail (VPIM) version 2 designed to support interoperability with
   desktop clients.  Other goals for this version of VPIM include
   expanded interoperability with unified messaging systems, conformance
   to Internet standards, and backward compatibility with voice
   messaging systems currently running in a VPIM enabled environment.
   This document does not include goals that were met fully by VPIM
   version 2.

1.  Introduction

   Until recently, voice mail and call answering services were
   implemented as stand-alone proprietary systems.  Today, standards
   such as the Voice Profile for Internet Mail (VPIM) enable
   interoperability between such systems over the Internet.  VPIM
   version 1 [VPIM1] was experimental and was a first attempt at a Voice
   Profile for Internet Mail, but is now classified as Historical.  VPIM
   Version 2 [VPIM2] is an improvement on VPIM version 1 that was
   originally intended to provide interoperability between voice
   messaging systems only.  It describes a messaging profile that
   standardizes the exchange of voice mail over an IP messaging network
   using SMTP [DRUMSMTP] and MIME [MIME1].

   Because the number of desktop boxes is growing rapidly and will soon
   approach the number of desktop telephones, it is essential to
   consider the requirements of desktop email client applications

   (including, but not limited to, MIME-compliant email clients).  With
   the trend toward integration of voice mail and email through unified
   messaging (UM), it is now necessary to define a profile that supports
   the needs of desktop applications and unified messaging systems
   (including Internet Facsimile [EXFAX]).  This profile is being
   referred to as Internet Voice Mail (IVM).

   This document defines the goals for Internet Voice Mail.  This
   standard will support the interchange of voice messages between voice
   mail systems, unified messaging systems, email servers, and desktop
   client applications.  The desktop client application is of particular
   and important interest to IVM.  This document will also expand the
   offerings of service providers by facilitating access to voice mail
   from a web client.

2.  Conventions used in this document

   The following terms have specific meaning in this document:

   "service"      An operational service offered by a service provider
   "application"  A use of systems to perform a particular function
   "terminal"     The endpoint of a communication application
   "goal"         An objective of the standardization process

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   "SHOULD", "SHOULD NOT", "RECOMMENDED",  "MAY", and "OPTIONAL" in this
   document are to be interpreted as described in BCP 14, RFC 2119
   [RFC2119].

3. Goals for Internet Voice Mail

3.1.  Interoperability

   Enhanced interoperability is the primary goal of IVM.  The profile
   MUST facilitate interoperability between voice mail systems, unified
   messaging systems, Internet email servers, and desktop client
   applications.  Such interoperability MUST support systems which
   combine multiple media types in a single message, as well as legacy
   voice mail and email systems.  It MUST allow the ability to
   accommodate varying capabilities of the voice mail, unified
   messaging, and email systems.  Furthermore, IVM MUST be compatible
   with Internet Fax (extended mode) proposed standards and VPIM
   messages that contain fax body parts.

   To have "interoperability" means that an IVM compliant sender
   attempting to send to a recipient will not fail because of
   incompatibility.  IVM MUST support interoperability amongst the
   systems listed below:

      - Desktop Email client applications
      - IVM-capable Voice Mail systems
      - IVM-capable unified messaging systems
      - Traditional email servers

   IVM SHOULD also support interoperability with VPIM version 2 Voice
   Mail Systems.

   IVM MUST include new functionality to facilitate access to voice mail
   messages from desktop applications.

   Overall interoperability requires interoperability for all message
   elements: body parts deemed essential for message validity MUST be
   preserved, essential information MUST be provided in a form that is
   accessible by the users, status codes [CODES] MUST be understood, and
   operations that are standard for each system SHOULD be supported.

3.1.1.  Interoperability with Desktop Email Client Applications

   Desktop email applications are typically text based.  The abilities
   to listen to, reply to, forward, and generate voice mail messages
   from a traditional desktop environment are relatively new
   developments.  To accommodate current use and future developments in
   this area, IVM MUST provide features to support access to voice mail
   messages from the desktop and other email-reading devices.  Also, web
   access to voicemail SHOULD be supported from the desktop.

   IVM SHOULD NOT require desktop email applications to possess a large
   amount of processing power, and a base level implementation MUST
   interoperate, even if it does not offer complex processing.  In order
   to support interoperability, at least one mandatory codec MUST be
   defined.  The mandatory codec(s) SHOULD be widely available on
   desktops.  For interoperability with VPIM version 2 systems, IVM
   applications MAY also support the VPIM v2 mandatory codec, 32KADPCM
   [ADPCM and G726-32].

   Any codecs included in the IVM specification SHOULD meet the
   following criteria:

      -  Availability on desktops: Codecs SHOULD be available on most
         platforms.

      -  Source code availability: Source code SHOULD be readily
         accessible.

      -  Decoding complexity: All codecs MUST be low complexity to
         decode.

      -  Encoding complexity: Some of the codecs MUST be low complexity
         to encode.

      -  Bit rate: IVM SHOULD specify a codec with low bit rate for
         devices (i.e., wireless) that do not have much space/bandwidth.

      -  Voice Over IP support: IVM SHOULD specify a codec that supports
         Voice over IP implementations.

   Voice Content MUST always be contained in an audio/basic content-
   type unless the originator is aware that the recipient can handle
   other content.  To enable future support of other formats, IVM SHOULD
   provide identification of the codec used without requiring
   interpretation of an audio format.  IVM MAY allow audio encodings and
   formats that are not identified in the IVM specification to support
   environments in which the sender is aware of the optimal encoding and
   format for the recipient.

   To address performance and bandwidth issues, IVM MAY support
   streaming of IVM audio to the desktop.  IVM MAY explicitly support
   formats other than raw audio to facilitate streaming.

   Because most email readers are text/html based and because many
   devices are not capable of recording audio content, IVM MUST allow
   inclusion of text body parts in a voice message.  IVM SHOULD NOT
   explicitly prohibit other media types as long as critical content is
   identified and minimal discard rules are specified.

   To support devices that have applications dedicated to specific media
   types or that are not capable of handling specific content, IVM
   SHOULD define a way to describe the content of the message,
   indicating how the content can be accessed.

   Desktop implementation of IVM MUST support attachments of any media
   type.

3.1.2.  Interoperability with IVM-capable Voice Messaging Systems

   Voice messaging systems are generally implemented as special-purpose
   machines that interface to a telephone switch and provide call
   answering and voice messaging services.  VPIM version 2 was designed
   to support interoperability between such systems and remains the best
   messaging profile for this purpose.

   To support interoperability between IVM voice messaging systems and
   other compliant systems, IVM SHOULD have a minimum set of required
   features that will guarantee interoperability, and also provision for
   additional functionality that may be supported by more complex
   systems.  IVM MUST define a mechanism for identifying essential
   content and status codes [CODES] indicating that a message could not
   be delivered due to capability differences.

   NOTE: IVM SHOULD provide some level of interoperability with VPIM
   version 2 voice messaging systems.  In order to support minimal
   interoperability between IVM and VPIM version 2, IVM systems MAY be
   able to receive the VPIM version 2 32KADPCM codec [ADPCM and G726-
   32], and MUST gracefully handle the case where a legacy receiving
   system does not support the IVM codecs.

3.1.3.  Interoperability with IVM-capable Unified Messaging Systems

   Unified messaging solutions typically leverage common store,
   directory, and transport layers to provide greater interoperability
   and accessibility to a variety of media content.  They support
   creation of and access to voicemail, email, and fax messages from a
   single user interface.

   To accommodate the common functionality of unified messaging systems,
   IVM MUST support the inclusion of body parts containing different
   media types.  It MUST also handle messages that contain VPIM messages
   as attachments to messages of another type (such as multipart/mixed),
   and VPIM messages that contain attachments of another type.

   To provide interoperability with systems that cannot handle a
   particular content type, IVM MUST provide a mechanism for identifying
   critical content and MAY define media specific status codes and
   strings to handle non-delivery of these body parts.

3.1.4.  Interoperability with Traditional Email Servers

   Traditional email servers are those that support only textual media
   as inline content.  IVM MUST interoperate consistently with the
   current Internet mail environment.  If an IVM message arrives in
   users' mailboxes, IVM MUST provide a mechanism to interoperate with
   common user practices for mail messages: storing them in databases,
   retransmission, forwarding, creation of mail digests, and replying to
   messages using non-audio equipment.

3.2.  Conformance to Existing Standards

   It is the goal of IVM to conform as closely as possible to existing
   standards while meeting the other goals defined in this document.

   -  Restrictions: The profile SHOULD impose as few restrictions as
      possible to existing Internet mail standards.  In particular, it
      MUST support all elements of RFC 2822 [DRUMSIMF], except those
      that prevent the profile from meeting other IVM goals.

   -  Additions: The profile SHOULD make as few additions as possible to
      existing internet mail standards.  It SHOULD adhere to existing
      desktop conventions in desktop-related areas such as file
      extensions.  If it is necessary to define new MIME types or sub-
      types, the IVM work group SHOULD propose terms that are already
      standard or in common use in the desktop environment.

3.3.  Backward Compatibility

   This profile SHOULD provide backward compatibility with VPIM version
   2 to the extent that the functionality required to meet the goals of
   this profile is not compromised.  Where backward compatibility is not
   possible, IVM SHOULD provide and define a minimal set of rules and
   status codes for handling non-delivery of IVM messages resulting from
   interoperability with VPIM version 2 systems and other legacy
   systems.

3.4.  Robustness

   IVM MUST be usable in an environment in which there exist legacy
   gateways that do not understand MIME.  Core features and critical
   data MUST not be lost when messages pass through AMIS gateways
   [AMIS-A and AMIS-D].  IVM SHOULD allow interoperability with
   recipient devices and gateways that have limited buffering
   capabilities and cannot buffer all header information.

3.5.  Security Considerations

   To facilitate security, IVM MUST support authenticated and/or
   encrypted voice messages.  In addition, IVM MUST adhere to the
   security issues identified in VPIM v2 [VPIM2] and in the other RFCs
   referenced by this document, especially SMTP [DRUMSMTP], Internet
   Message Format [DRUMSIMF], and MIME [MIME1].

4.  References

4.1.  Normative References

   [ADPCM]    Vaudreuil, G. and G. Parsons, "Toll Quality Voice - 32
              kbit/s ADPCM: MIME Sub-type Registration", RFC 2422,
              September 1998.

   [AMIS-A]   Audio Messaging Interchange Specifications (AMIS) - Analog
              Protocol Version 1, Issue 2, February 1992.

   [AMIS-D]   Audio Messaging Interchange Specifications (AMIS) -
              Digital Protocol Version 1, Issue 3 August 1993.

   [CODES]    Vaudreuil, G., "Enhanced Mail System Status Codes", RFC
              3463, January 2003.

   [DRUMSMTP] Klensin, J., "Simple Mail Transfer Protocol", RFC 2821,
              April 2001.

   [DRUMSIMF] Resnick, P., "Internet Message Format", RFC 2822, April
              2001.

   [EXFAX]    Masinter, L. and D. Wing, "Extended Facsimile Using
              Internet Mail", RFC 2532, March 1999.

   [G726-32]  CCITT Recommendation G.726 (1990), General Aspects of
              Digital Transmission Systems, Terminal Equipment - 40,
              32,24,16 kbit/s Adaptive Differential Pulse Code
              Modulation (ADPCM).

   [MIME1]    Freed, N. and N. Borenstein, "Multipurpose Internet Mail
              Extensions (MIME) Part One: Format of Internet Message
              Bodies", RFC 2045, November 1996.

   [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
              Requirement Levels", BCP 14, RFC 2119, March 1997.

   [VPIM2]    Vaudreuil, G. and G. Parsons, "Voice Profile for Internet
              Mail, Version 2", RFC 2421, September 1998.

4.2.  Informative References

   [VPIM1]    Vaudreuil, Greg, "Voice Profile for Internet Mail", RFC
              1911, February 1996.

   [VPIM3]    Silvestro, L. and R. Miles, "Goals for Voice Profile for
              Internet Mail, Version 3", Work in Progress, March 2000.

5.    Acknowledgments

   This document is the final result of an evolving requirements
   document that started with VPIM v3 and evolved into an alternative
   specification for a different (i.e., end-to-end instead of server-
   to-server) application.  The basis for this document was written by
   Laile Di Silvestro and Rod Miles [VPIM3].

   The author gratefully acknowledges the authors of [VPIM3], and the
   input and feedback provided by the members of the EMA and IETF VPIM
   work groups.

6.  Author's Address

   Emily Candell
   Comverse
   200 Quannapowitt Parkway
   Wakefield, MA 01803
   Phone: +1-781-213-2324
   EMail: emily.candell@comverse.com

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