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VPIM Working Group                                         Stuart McRae
Internet Draft                                                      IBM
Document: <draft-ietf-vpim-ivm-03.txt>                    Glenn Parsons
Category: Standards Track                               Nortel Networks
                                                      November 21, 2001

                         Internet Voice Messaging

Status of this Memo

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

   Internet-Drafts are working documents of the Internet Engineering
   Task Force (IETF), its areas, and its working groups. Note that
   other groups may also distribute working documents as Internet-
   Drafts. Internet-Drafts are draft documents valid for a maximum of
   six months and may be updated, replaced, or obsoleted by other
   documents at any time. It is inappropriate to use Internet-Drafts as
   reference material or to cite them other than as "work in progress."
   The list of current Internet-Drafts can be accessed at
   The list of Internet-Draft Shadow Directories can be accessed at

1. Abstract

   This document provides for the carriage of voicemail messages over
   Internet mail as part of a unified messaging infrastructure.

   The Internet Voice Messaging (IVM) concept described in this
   document is not a successor format to VPIM v2, but rather an
   alternative specification for a different application.

2. Conventions used in this document

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   this document are to be interpreted as described in RFC-2119

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3. Introduction

   People naturally communicate using their voices, and this is
   preferable to typing for some forms of communication. By permitting
   voicemail to be implemented in an interoperable way on top of
   Internet Mail, voice messaging and electronic mail need no longer
   remain separate, isolated worlds and users will be able to choose
   the most appropriate form of communication. This will also enable
   new types of device, without keyboards, to be used to participate in
   electronic messaging when mobile, in a hostile environment, or in
   spite of disabilities.

   There exist unified messaging systems which will transmit voicemail
   messages over the Internet using SMTP/MIME, but these systems suffer
   from a lack of interoperability because various aspects of such a
   message have not hitherto been standardized. In addition, voicemail
   systems can now conform to the Voice Profile for Internet Messaging
   (VPIM v2 as defined in RFC 2421 [VPIM2] and being clarified for
   Draft Standard in [VPIMV2R2]) when forwarding messages to remote
   voicemail systems, but VPIM v2 was designed to allow two voicemail
   systems to exchange messages, not to allow a voicemail system to
   interoperate with a desktop e-mail client, and it is often not
   reasonable to expect a VPIM v2 message to be usable by an e-mail
   recipient. The result is messages which cannot be processed by the
   recipient (e.g., because of the encoding used), or look ugly to the

   This document therefore proposes a new standard mechanism for
   representing a voicemail message within SMTP/MIME, and a standard
   encoding for the audio content, which unified messaging systems and
   mail clients MUST implement to ensure interoperability. By using a
   standard SMTP/MIME representation, and a widely implemented audio
   encoding, this will also permit most users of e-mail clients not
   specifically implementing the standard to still access the voicemail
   message. In addition, this document describes features an e-mail
   client SHOULD implement to allow recipient's to display voicemail
   message in a more friendly, context sensitive way to the user, and
   intelligently provide some of the additional functionality typically
   found in voicemail systems (such as responding with a voice message
   instead of e-mail). Finally is explained how a client MAY provide a
   level of interoperability with VPIM v2.

   It is desirable that unified messaging mail clients also be able to
   fully interoperate with voicemail servers. This is possible today,
   providing the client implements VPIM v2 [VPIMV2] in addition to this
   specification, and uses it to construct messages to be sent to a
   voicemail server.

   The definition in this document is based on the IVM Requirements
   document [GOALS].  It references separate work on critical content
   [CRITICAL] and message context [HINT]. Addressing and directory
   issues are discussed in related documents [ADDRESS], [VPIMENUM],

   Further information on VPIM and related activities can be found at
   http://www.vpim.org or http://www.ema.org/vpim.

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4. Message Format

   Voice messages may be created explicitly by a user (e.g. recording a
   voicemail message in their mail client) or implicitly by a unified
   messaging system (when it records a telephone message).

   All messages MUST conform with the Internet Mail format, as updated
   by the DRUMS working group [DRUMSIMF].

   When creating a voice message from a client supporting IVM, the
   message header MUST indicate a message context of "voice-message"
   (see [HINT]). However, to support interoperability with clients not
   explicitly supporting IVM a recipient MUST NOT require its presence
   in order to correctly process voice messages.

   If the receiving user agent identifies the message as a voice
   message (from the message context), it MAY present it to the user as
   a voice message rather than as an electronic mail message with a
   voice attachment (see [BEHAVIOUR]).

   Any content type is permitted in a message, but the top level
   content type on origination of a new, forwarded or reply voice
   message SHOULD be multipart/mixed. If the recipient is known to be
   VPIM v2 compliant then multipart/voice-message MAY be used instead
   (in which case all the provisions of [VPIMV2R2] MUST be implemented
   in constructing the message).

   If the message was created as a voice message, and so is not useful
   if the audio content is omitted, then the appropriate audio body part
   MUST be indicated as critical content, via a Criticality parameter
   of CRITICAL on the Content-Disposition (see [CRITICAL]). Additional
   important body parts (such as the original audio message if a
   voicemail is being forwarded) MAY also be indicated via a
   Criticality of CRITICAL. Contents which are not essential to
   communicating the meaning of the message (e.g., an associated vCard
   for the originator) MAY be indicated via a Criticality of IGNORE.

   When forwarding IVM messages clients MUST preserve the content type
   of all audio body parts in order to ensure that the new recipient is
   able to play the forwarded messages.

   The top level content type on origination of a delivery notification
   message MUST be multipart/report. This will allow automatic
   processing of the delivery notification - for example, so that text-
   to-speech processing can render a non-delivery notification in the
   appropriate language for the recipient.

5. Transport

   The message MUST be transmitted in accordance with the Simple Mail
   Transport Protocol, as updated by the DRUMS working group

   Delivery Status Notifications MAY be requested [DSN] if delivery of
   the message is important to the originator and a mechanism exists to

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   return status indications to them (which may not be possible for
   voicemail originators).

6. Addressing

   Any valid Internet Mail address may be used for a voice message.

   It is desirable to be able to use and onramp/offramp for delivery of
   a voicemail message to a user, which will result in specific
   addressing requirements, based on service selectors as defined in
   [SELECTOR]. Further discussion of addressing requirements for voice
   messages can be found in the VPIM Addressing document [ADDRESS].

   It is desirable to permit the use of a directory service to map
   between the E.164 phone number of the recipient and an SMTP mailbox
   address. A discussion on how this may be achieved using the ENUM
   infrastructure is in [VPIMENUM].  A definition of the VPIM LDAP
   schema that a system would use is found in [SCHEMA].

   If a message is created and stored as a result of call answering,
   the caller's name and number MAY be stored in the message headers in
   its original format per [CLID].

7. Notifications

   Delivery Status Notifications MUST be supported.  All non-delivery
   of messages MUST result in a NDN, if requested [DSN]. If the
   receiving system supports content criticality and is unable to
   process all of the critical media types within a voice message
   (indicated by the content criticality), then it MUST non-deliver the
   entire message per [CRITICAL].

   Message Disposition Notifications SHOULD be supported (but according
   to MDN rules the user MUST be given the option of deciding whether
   MDNs are returned) per [MDN].

   If the recipient is unable to display all of the indicated critical
   content components indicated, then it SHOULD give the user the
   option of returning an appropriate MDN (see [CRITICAL]).

8. Voice Contents

   Voice messages may be contained at any location within a message and
   MUST always be contained in either an audio/wav or audio/basic
   content-type unless the originator is aware that the recipient can
   handle other content. Specifically, Audio/32kadpcm MAY be used when
   the recipient is known to support VPIM v2 [VPIMV2].

   The VOICE parameter on Content-Disposition from VPIM v2 [VPIMV2]
   SHOULD be used to identify the any spoken names or spoken subjects
   (as distinct from voice message contents).

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   The originator's spoken name MAY be included with messages as
   separate audio contents, if known, and indicated by the Content-
   Disposition VOICE parameter as defined in VPIM v2 [VPIMV2].  If
   there is a single recipient for the message, their spoken name MAY
   also be included (per VPIM v2). A spoken subject MAY also be
   provided (per VPIM v2).

   A sending implementation MAY determine the recipient capabilities
   before sending a message and choose a codec accordingly (e.g., using
   some form of content negotiation).  In the absence of such recipient
   knowledge, sending implementations MUST use either:  MS-GSM with a
   WAV header - indicated via "audio/wav; codec=31" [MSGSM],[WAV]; or
   raw G.711 mu-law - indicated via "audio/basic" [G711],[MIME2].  A
   sending implementation MAY support interoperability with VPIM v2
   [VPIMV2], in which case it MUST be able to record G.726 (indicated
   as audio/32kadpcm)[G726],[ADPCM].

   Recipients MUST be able to play both a WAV encapsulated MS-GSM and a
   raw G.711 mu-law message, and MAY be able to play G.726 (indicated
   as audio/32kadpcm) to provide interoperability with VPIM v2.  A
   receiving implementation MAY also be able to play messages encoded
   with other codecs (either natively or via transcoding).

   These requirements may be summarized as follows:

      Codec           No VPIM v2 Support      With VPIM V2 Support
                      Record    Playback      Record      Playback
      -------------   ------    --------      ------      --------
      MS-GSM in WAV    MAY*      MUST          MAY*        MUST
      G.711 mu-law     MAY*      MUST          MAY*        MUST
      G.726            MAY       MAY           MUST        MUST
      Other            MAY       MAY           MAY         MAY

                 *MUST record at least one

9. Fax Contents

   Fax contents SHOULD be carried according to RFC 2532 [IFAX].

10. Interoperability with VPIM v2

   Interoperability between VPIM v2 systems and IVM systems can take a
   number of different forms. While a thorough investigation of how
   full interoperability might be provided between IVM and VPIM v2
   systems is beyond the scope of this document, three key alternatives
   are discussed below.

10.1 Handling VPIM v2 Messages in an IVM client

   If an IVM conformant client is able to process a content type of
   multipart/voice-message (by treating it as multipart/mixed) and play
   a G.726 encoded audio message within it (indicated by a content type
   of audio/32kadpcm), then a VPIM v2 message which gets routed to that
   desktop will be at least usable by the recipient.

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   This delivers a level of partial interoperability which would ease
   the life of end users. However, care should be taken to ensure that
   any attempt to reply to such a message does not result in an invalid
   VPIM v2 message being sent to a VPIM v2 system.  Note that replying
   to an e-mail user who has forwarded a VPIM v2 message to you is,
   however, acceptable.

   A conformant IVM implementation MUST NOT send a non-VPIM v2 messages
   to something it knows to be a VPIM v2 system, unless it also knows
   that the destination system can handle such a message (even though
   VPIM v2 systems are encouraged to handle non-VPIM v2 messages in a
   graceful manner). In general, it must be assumed that if a system
   sends you a conformant VPIM v2 message, then it is a VPIM v2 system
   and so you may only reply with a VPIM v2 compliant message (unless
   you know by some other means that the system supports IVM).

   In addition, it should be noted that an IVM client may well not
   fully conform to VPIM v2 even if it supports playing a G.726 message
   (e.g., it may not respect the handling of the Sensitivity field
   required by VPIM v2).  This is one reason why VPIM v2 systems may
   choose not to route messages to any system they do not know to be
   VPIM v2 compliant.

10.2 Dual Mode Systems and Clients

   A VPIM v2 system could be extended to also be able to support IVM
   compliant messages, and an IVM conformant client could be extended
   to implement VPIM v2 in full when corresponding with a VPIM v2
   compliant systems. This is simply a matter of implementing both
   specifications and selecting the appropriate one depending on the
   received message content or the recipient's capabilities.  This
   delivers full interoperability for the relevant systems, providing
   the capabilities of the target users can be determined.

   Note that the mechanism for determining if a given recipient is
   using a VPIM v2 system or client is outside of the scope of this
   specification.  Various mechanisms for capabilities discovery exist
   which could be applied to this problem, but no standard solution has
   yet been defined.

10.3 Gateways

   It would be possibly to build a gateway linking a set of VPIM v2
   users with a set of IVM users.  This gateway would implement the
   semantics of the two worlds, and translate between them according to
   defined policies.

   For example, VPIM v2 messages with a Sensitivity of Private might be
   rejected instead of being forwarded to an IVM recipient, because it
   might not implement the semantics of a Private message, while an IVM
   message containing content not supported in VPIM v2 (e.g., a PNG
   image) with a Criticality of CRITICAL would be rejected in the

   Such a gateway MUST fully implement this specification and the VPIM
   v2 specification [VPIMV2R2] unless it knows somehow that the

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   specific originators/recipients support capabilities beyond those
   required by these standards.

11. Security Considerations

   It is anticipated that there are no additional security issues
   beyond those identified in VPIM v2 [VPIMV2R2] and in the other RFCs
   referenced by this document, especially SMTP [DRUMSMTP], Internet
   Message Format [DRUMSIMF], MIME [MIME2], Critical Content [CRITICAL]
   and Message Context [HINT].

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12. References

   [ADDRESS] Parsons, G., "VPIM Addressing", <draft-ietf-vpim-address-
   01.txt>, April 2001, Work in Progress.

   [ADPCM] G. Vaudreuil and G. Parsons, "Toll Quality Voice - 32 kbit/s
   ADPCM:  MIME Sub-type Registration", RFC 2422, September 1998.
   Revised by:  <draft-ietf-vpim-vpimv2r2-32k-02.txt>, October 2001.

   [BEHAVIOUR] Parsons, G., Maruszak, J., "Voice Messaging Client
   Behaviour", <draft-ema-vpim-cb-02.txt>, July 2001, Work in Progress.

   [CLID] Parsons, G., Maruszak, J., "Calling Line Identification for
   VPIM Messages", <draft-ema-vpim-clid-02.txt>, June 2001, Work in

   [CRITICAL] Burger, E., Candell, E., "Critical Content of Internet
   Mail" <draft-burger-vpim-cc-04.txt>, April 2001, Work in Progress.

   [DSN] Moore, K., "SMTP Service Extension for Delivery Status
   Notifications" RFC 1891, January 1996.

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

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

   [DUR] G. Parsons and G. Vaudreuil, "Content Duration MIME Header
   Definition", RFC 2424, September 1998. Revised by:  <draft-ietf-
   vpim-vpimv2r2-dur-02.txt>, October 2001, Work in Progress.

   [GOALS] Candell, E., "Goals for Internet Voice Mail", <draft-ietf-
   vpim-ivm-goals-03.txt>, April 2001, Work in Progress.

   [G726] 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).

   [G711] ITU-T Recommendation G.711 (1993), General Aspects of Digital
   Transmission Systems, Terminal Equipment - Pulse Code Modulation
   (PCM) of Voice Frequencies.

   [HINT]  Burger, E., Candell, E., Eliot, C., Klyne, G. "Message
   Context Internet Mail" <draft-ietf-vpim-hint-07.txt>, June 2001,
   Work in Progress.

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

   [KEYWORDS] Bradner, S., "Key Words for use in RFCs To Indicate
   Requirement Levels", RFC 2119, March 1997.

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

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   [MIME2] N. Freed and N. Borenstein,  "Multipurpose Internet Mail
   Extensions (MIME) Part Two: Media Types ", RFC 2046, Innosoft, First
   Virtual, November 1996.

   [MSGSM]   Di Silvestro, L., Hedberg, E., Baribault, G., "Microsoft
   GSM MIME Sub-type Registration" <draft-ema-vpim-wav-00.txt>, April
   1999, Work in Progress (expired).

   [SELECTOR] Allocchio, C., "Minimal PSTN address format in Internet
   Mail", RFC 2303, March 1998.

   [SCHEMA] Vaudreuil, G. "Voice Messaging Directory Service",<draft-
   ietf-vpim-vpimdir-01.txt> , November 2001, Work in Progress.

   [VPIMENUM] Vaudreuil, G. "Voice Message Routing Service", <draft-
   ietf-vpim-routing-02.txt> , October 2001, Work in Progress.

   [VPIMV2]   Vaudreuil, G., Parsons, G., "Voice Profile for Internet
   Mail -  version 2", RFC 2421, September 1998.

   [VPIMV2R2]   Vaudreuil, G., Parsons, G., "Voice Profile for Internet
   Mail - version 2", <draft-ietf-vpim-vpimv2r2-04.txt>, October 2001,
   Work in Progress.

   [WAV]   Di Silvestro, L., Baribault, G., "Waveform Audio File Format
   MIME Sub-type Registration" <draft-ema-vpim-wav-00.txt>, April 1999,
   Work in Progress (expired).

13. Author's Addresses

   Stuart J. McRae
   43 Seymour Gardens
   Twickenham, United Kingdom
   TW1 3AR

   Phone: +44 208 891 1896
   Fax: +44 1784 499 112
   Email: stuart.mcrae@uk.ibm.com

   Glenn W. Parsons
   Nortel Networks
   P.O. Box 3511, Station C
   Ottawa, ON K1Y 4H7

   Phone: +1-613-763-7582
   Fax: +1-416-597-7005
   Email: gparsons@nortelnetworks.com

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14.  Full Copyright Statement

   Copyright (C) The Internet Society (2001).  All Rights Reserved.

   This document and translations of it may be copied and furnished to
   others, and derivative works that comment on or otherwise explain it
   or assist in its implementation may be prepared, copied, published
   and distributed, in whole or in part, without restriction of any
   kind, provided that the above copyright notice and this paragraph
   are included on all such copies and derivative works.  However, this
   document itself may not be modified in any way, such as by removing
   the copyright notice or references to the Internet Society or other
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   The limited permissions granted above are perpetual and will not be
   revoked by the Internet Society or its successors or assigns.

   This document and the information contained herein is provided on an

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