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Network Working Group                                           S. McRaeRequest for Comments: 4239                                           IBMCategory: Standards Track                                     G. Parsons                                                         Nortel Networks                                                           November 2005Internet Voice Messaging (IVM)Status of This Memo   This document specifies an Internet standards track protocol for the   Internet community, and requests discussion and suggestions for   improvements.  Please refer to the current edition of the "Internet   Official Protocol Standards" (STD 1) for the standardization state   and status of this protocol.  Distribution of this memo is unlimited.Copyright Notice   Copyright (C) The Internet Society (2005).Abstract   This document describes 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 (Voice Profile for Internet Mail   Version 2), but rather an alternative specification for a different   application.1.  Introduction   For some forms of communication, people prefer to communicate using   their voices rather than typing.  By permitting voicemail to be   implemented in an interoperable way on top of Internet Mail, voice   messaging and electronic mail no longer need to remain in separate,   isolated worlds, and users will be able to choose the most   appropriate form of communication.  This will also enable new types   of devices, 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 that 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 MessagingMcRae & Parsons             Standards Track                     [Page 1]

RFC 4239                Internet Voice Messaging           November 2005   (VPIM v2 as defined inRFC 2421 [VPIMV2] and revised inRFC 3801,   Draft Standard [VPIMV2R2]) when forwarding messages to remote   voicemail systems.  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.  It is often not   reasonable to expect a VPIM v2 message to be usable by an e-mail   recipient.  The result is messages that cannot be processed by the   recipient (e.g., because of the encoding used), or look ugly to the   user.   This document therefore proposes a 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   messages.  In addition, this document describes features an e-mail   client SHOULD implement to allow recipients to display voicemail   messages 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, how a client MAY provide a level of   interoperability with VPIM v2 is explained.   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 [VPIMV2R2], 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],   [SCHEMA].   Further information on VPIM and related activities can be found athttp://www.vpim.org orhttp://www.ema.org/vpim.2.  Conventions Used in This Document   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 inRFC-2119 [KEYWORDS].McRae & Parsons             Standards Track                     [Page 2]

RFC 4239                Internet Voice Messaging           November 20053.  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], and the MIME format [MIME1].   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.   The receiving agent MUST be able to support multipart messages   [MIME5].  If the receiving user agent identifies the message as a   voice message (from the message context), it SHOULD 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 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 that 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 a 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.McRae & Parsons             Standards Track                     [Page 3]

RFC 4239                Internet Voice Messaging           November 20054.  Transport   The message MUST be transmitted in accordance with the Simple Mail   Transport Protocol, as updated by the DRUMS working group [DRUMSMTP].   Delivery Status Notifications MAY be requested [DSN] if delivery of   the message is important to the originator and a mechanism exists to   return status indications to them (which may not be possible for   voicemail originators).5.  Addressing   Any valid Internet Mail address may be used for a voice message.   It is desirable to be able to use an onramp/offramp for delivery of a   voicemail message to a user, which will result in specific addressing   requirements, based on service selectors 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].6.  Notifications   Delivery Status Notifications MUST be supported.  All non-delivery of   messages MUST result in an NDN, if requested [DSN,DSN2,DSN3,DSN4].   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]).McRae & Parsons             Standards Track                     [Page 4]

RFC 4239                Internet Voice Messaging           November 20057.  Voice Contents   Voice messages may be contained at any location within a message and   MUST always be contained in an 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 [VPIMV2R2].   The VOICE parameter on Content-Disposition from VPIM v2 [VPIMV2R2]   SHOULD be used to identify any spoken names or spoken subjects (as   distinct from voice message contents).  As well, the Content-Duration   header [DUR] SHOULD be used to indicate the audio length.   The originator's spoken name MAY be included with messages as   separate audio contents, if known, and SHOULD be indicated by the   Content-Disposition VOICE parameter as defined in VPIM v2 [VPIMV2R2].   If there is a single recipient for the message, the 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 raw G.711 mu-law, which   is indicated with a MIME content type of "audio/basic" (and SHOULD   use a filename parameter that ends ".au") [G711], [MIME2].  A sending   implementation MAY support interoperability with VPIM v2 [VPIMV2R2],   in which case, it MUST be able to record G.726 (indicated as   audio/32kadpcm) [G726], [ADPCM].   Recipients MUST be able to play 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   -------------   ------    --------      ------      --------   G.711 mu-law     MUST      MUST          MUST        MUST   G.726            *         MAY           MUST        MUST   Other            *         MAY           *           MAY      * = MUST NOT, but MAY only if recipient capabilities knownMcRae & Parsons             Standards Track                     [Page 5]

RFC 4239                Internet Voice Messaging           November 20058.  Fax Contents   Fax contents SHOULD be carried according toRFC 2532 [IFAX].9.  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.9.1.  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 that gets routed to that   desktop will be at least usable by the recipient.   This delivers a level of partial interoperability that 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 message   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 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.9.2.  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 compliantMcRae & Parsons             Standards Track                     [Page 6]

RFC 4239                Internet Voice Messaging           November 2005   system.  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   that could be applied to this problem, but no standard solution has   yet been defined.9.3.  Gateways   It would be possible 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 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   gateway.   Such a gateway MUST fully implement this specification and the VPIM   v2 specification [VPIMV2R2], unless it knows somehow that the   specific originators/recipients support capabilities beyond those   required by these standards.10.  Security Considerations   This document presents an optional gateway between IVM and VPIM   systems.  Gateways are inherently lossy systems and not all   information can be accurately translated.  This applies to both the   transcoding of the voice and the translation of features.  Two   examples of feature translation are given in 9.3, but the risk   remains that different gateways will handle the translation   differently since it is undefined in this document.  This may lead to   unexpected behavior through gateways.   In addition, gateways present an additional point of attack for those   interested in compromising a messaging system.  If a gateway is   compromised, "monkey in the middle" attacks, conducted from the   compromised gateway, may be difficult to detect or appear to be   authorized transformations.McRae & Parsons             Standards Track                     [Page 7]

RFC 4239                Internet Voice Messaging           November 2005   Aside from the gateway issue, it is anticipated that there are no new   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].11.  References11.1.  Normative References   [ADDRESS]    Parsons, G., "Voice Profile for Internet Mail (VPIM)                Addressing",RFC 3804, June 2004.   [ADPCM]      Vaudreuil, G. and G. Parsons, "Toll Quality Voice - 32                kbit/s Adaptive Differential Pulse Code Modulation                (ADPCM) MIME Sub-type Registration",RFC 3802, June                2004.   [BEHAVIOUR]  Parsons, G. and J. Maruszak, "Voice Messaging Client                Behaviour",RFC 4024, July 2005.   [CLID]       Parsons, G. and J. Maruszak, "Calling Line                Identification for Voice Mail Messages",RFC 3939,                December 2004.   [CRITICAL]   Burger, E., "Critical Content Multi-purpose Internet                Mail Extensions (MIME) Parameter",RFC 3459, January                2003.   [DSN]        Moore, K., "Simple Mail Transfer Protocol (SMTP) Service                Extension for Delivery Status Notifications (DSNs)",RFC3461, January 2003.   [DSN2]       Vaudreuil, G., "The Multipart/Report Content Type for                the Reporting of Mail System Administrative Messages",RFC 3462, January 2003.   [DSN3]       Vaudreuil, G., "Enhanced Mail System Status Codes",RFC3463, January 2003.   [DSN4]       Moore, K. and G. Vaudreuil, "An Extensible Message                Format for Delivery Status Notifications",RFC 3464,                January 2003.   [DRUMSMTP]   Klensin, J., "Simple Mail Transfer Protocol",RFC 2821,                April 2001.McRae & Parsons             Standards Track                     [Page 8]

RFC 4239                Internet Voice Messaging           November 2005   [DRUMSIMF]   Resnick, P., "Internet Message Format",RFC 2822, April                2001.   [DUR]        Vaudreuil, G. and G. Parsons, "Content Duration MIME                Header Definition",RFC 3803, June 2004.   [HINT]       Burger, E., Candell, E., Eliot, C., and G. Klyne,                "Message Context for Internet Mail",RFC 3458, January                2003.   [IFAX]       Masinter, L. and D. Wing, " Extended Facsimile Using                Internet Mail",RFC 2532, March 1999.   [KEYWORDS]   Bradner, S., "Key words for use in RFCs to Indicate                Requirement Levels",BCP 14,RFC 2119, March 1997.   [MDN]        Hansen, T. and G. Vaudreuil, "Message Disposition                Notification",RFC 3798, May 2004.   [MIME1]      Freed, N. and N. Borenstein, "Multipurpose Internet Mail                Extensions (MIME) Part One: Format of Internet Message                Bodies",RFC 2045, November 1996.   [MIME2]      Freed, N. and N. Borenstein, "Multipurpose Internet Mail                Extensions (MIME) Part Two: Media Types",RFC 2046,                November 1996.   [MIME5]      Freed, N. and N. Borenstein, "Multipurpose Internet Mail                Extensions (MIME) Part Five: Conformance Criteria and                Examples",RFC 2049, November 1996.   [SELECTOR]   Allocchio, C., "Minimal GSTN address format in Internet                Mail",RFC 3191, October 2001.   [SCHEMA]     Vaudreuil, G., "Voice Messaging Directory Service",RFC4237, October 2005.   [VPIMENUM]   Vaudreuil, G., "Voice Message Routing Service",RFC4238, October 2005.   [VPIMV2]     Vaudreuil, G. and G. Parsons, "Voice Profile for                Internet Mail -  version 2",RFC 2421, September 1998.   [VPIMV2R2]   Vaudreuil, G. and G. Parsons, "Voice Profile for                Internet Mail - version 2 (VPIMv2)",RFC 3801, June                2004.McRae & Parsons             Standards Track                     [Page 9]

RFC 4239                Internet Voice Messaging           November 200511.2.  Informative References   [GOALS]      Candell, E., "High-Level Requirements for Internet Voice                Mail",RFC 3773, June 2004.   [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.Authors' Addresses   Stuart J. McRae   IBM   Lotus Park, The Causeway<   Staines, TW18 3AG   United Kingdom   Phone: +44 1784 445 112   Fax: +44 1784 499 112   EMail: stuart.mcrae@uk.ibm.com   Glenn W. Parsons   Nortel Networks   3500 Carling Avenue   Ottawa, ON K2H 8E9   Canada   Phone: +1-613-763-7582   Fax: +1-613-967-5060   EMail: gparsons@nortel.comMcRae & Parsons             Standards Track                    [Page 10]

RFC 4239                Internet Voice Messaging           November 2005Full Copyright Statement   Copyright (C) The Internet Society (2005).   This document is subject to the rights, licenses and restrictions   contained inBCP 78, and except as set forth therein, the authors   retain all their rights.   This document and the information contained herein are provided on an   "AS IS" basis and THE CONTRIBUTOR, THE ORGANIZATION HE/SHE REPRESENTS   OR IS SPONSORED BY (IF ANY), THE INTERNET SOCIETY AND THE INTERNET   ENGINEERING TASK FORCE DISCLAIM ALL WARRANTIES, EXPRESS OR IMPLIED,   INCLUDING BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF THE   INFORMATION HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED   WARRANTIES OF MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE.Intellectual Property   The IETF takes no position regarding the validity or scope of any   Intellectual Property Rights or other rights that might be claimed to   pertain to the implementation or use of the technology described in   this document or the extent to which any license under such rights   might or might not be available; nor does it represent that it has   made any independent effort to identify any such rights.  Information   on the procedures with respect to rights in RFC documents can be   found inBCP 78 andBCP 79.   Copies of IPR disclosures made to the IETF Secretariat and any   assurances of licenses to be made available, or the result of an   attempt made to obtain a general license or permission for the use of   such proprietary rights by implementers or users of this   specification can be obtained from the IETF on-line IPR repository athttp://www.ietf.org/ipr.   The IETF invites any interested party to bring to its attention any   copyrights, patents or patent applications, or other proprietary   rights that may cover technology that may be required to implement   this standard.  Please address the information to the IETF at ietf-   ipr@ietf.org.Acknowledgement   Funding for the RFC Editor function is currently provided by the   Internet Society.McRae & Parsons             Standards Track                    [Page 11]