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Versions: 00 01 02 03 04 05 06 07 RFC 3458

Network Working Group                                           E. Burger
Internet Draft                                   Centigram Communications
Document: draft-ietf-vpim-hint-00.txt                          E. Candell
Obsoletes: draft-burger-vpim-pc-00.txt           Comverse Network Systems
Category: Standards Track                                        C. Eliot
Expires in six Months                               Microsoft Corporation
                                                                 G. Klyne
                                                     Content Technologies
                                                            July 14, 2000


                     Content Hint for Internet Mail

Status of this Memo

   This document is an Internet-Draft and is in full conformance with
   all provisions of Section 10 of RFC2026 [1].

   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
   http://www.ietf.org/ietf/1id-abstracts.txt

   The list of Internet-Draft Shadow Directories can be accessed at
   http://www.ietf.org/shadow.html.


1.   Abstract

   This document describes a mechanism to allow senders of a multi-part
   Internet mail message to convey presentational information on the
   message as a whole.  The document specifies a RFC 822 header called
   "Content-Hint".  This mechanism is very similar to the use of the
   Content-Disposition MIME entity described in [2].  Content-
   Disposition gives clues to the receiving User Agent (UA) for how to
   display a given body part.  Content-Hint gives clues to the
   receiving UA for the context of the message display.  This allows
   the receiving UA to present the message in a meaningful way to the
   recipient.

   This mechanism is needed because examining the message itself is
   insufficient to determine the context of the message.  For example,
   one can envision a UA that distinguishes between a voice mail
   message with a text annotation and a text message with an audio
   attachment.  Content-Hint would provide the hint to the receiving UA
   which context to present the message.

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Table of Contents

1.  ABSTRACT .........................................................1
2.  CONVENTIONS USED IN THIS DOCUMENT ................................2
3.  MOTIVATION AND GOALS .............................................3

3.1.  The problem ....................................................3
3.2.  Some messaging scenarios .......................................4
3.2.1.    Internet e-mail.............................................4
3.2.2.    Short text messaging service................................5
3.2.3.    Facsimile...................................................5
3.2.4.    Voice mail..................................................6
3.2.5.    Multimedia message..........................................6
3.3.  The goal .......................................................7

4.  FUNCTIONAL REQUIREMENTS ..........................................7
5.  THE CONTENT-HINT .................................................7
6.  CONTENT-HINT REFERENCE FIELD .....................................8
6.1.  Content-Hint Syntax ............................................8
6.2.  content-hint Syntax ............................................8
6.2.1.    voice-message...............................................9
6.2.2.    fax-message.................................................9

6.2.3.    video-message...............................................9
6.2.4.    sms-message.................................................9
6.2.5.    none........................................................9
7.  SECURITY CONSIDERATIONS ..........................................9
8.  IANA CONSIDERATIONS .............................................10
8.1.  Content-Hint Registration .....................................10
8.2.  Primary Content Type Registrations ............................11
8.2.1.    voice-message..............................................11

8.2.2.    fax-message................................................11
8.2.3.    video-message..............................................12
8.2.4.    sms-message................................................13
9.  REFERENCES ......................................................14
10. ACKNOWLEDGMENTS .................................................14
11. AUTHOR'S ADDRESSES ..............................................15


2.   Conventions used in this document

   This document refers generically to the sender of a message in the
   masculine (he/him/his) and the recipient of the message in the
   feminine (she/her/hers).  This convention is purely for convenience
   and makes no assumption about the gender of a message sender or
   recipient.

   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 RFC-2119 [3].


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   FORMATTING NOTE: Notes, such at this one, provide additional
   nonessential information that the reader may skip without missing
   anything essential.  The primary purpose of these non-essential
   notes is to convey information about the rationale of this document,
   or to place this document in the proper historical or evolutionary
   context.  Readers whose sole purpose is to construct a conformant
   implementation may skip such information.  However, it may be of use
   to those who wish to understand why we made certain design choices.


3.   Motivation and goals

  3.1. The problem

   Multimedia messaging systems receive messages that may be presented
   in variety of ways.  For example, traditional e-mail uses simple
   text messages that the recipient displays and edits.  An UA may
   automatically print Fax images.  Another UA may play voice messages
   through a telephone handset.  Likewise, the receiving desktop
   computer may process and/or present documents transferred over e-
   mail using a local application.  Emerging and future developments
   may deliver other forms of information that have their own
   characteristics for user presentation, such as video messages and
   short text messages.

   An often-requested characteristic for multimedia messaging systems
   is to collect received messages in a "universal inbox", and to offer
   them to the user as a combined list.

   In the context of "unified messaging" different message media may
   have different implied semantics.  For example, some users may
   perceive voicemail to have an implicit assumption of urgency.  Thus
   they may wish to gather them together and process them before other
   messages.  Thus the end-user receiving agent needs to be able to
   identify voicemail and distinguish it from other messages.

   The uses of this kind of presentation characteristic for each
   message is multi-fold:

   o    display an indication to the user (e.g. by a suitably evocative
        icon along with other summary fields),

   o    auto-forwarding a specific message type into another messaging
        environment? (e.g., short text to a mobile short message
        service),

   o    prioritizing and grouping messages in an inbox display list,

   o    suggesting appropriate default handling for presentation,



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   o    suggesting appropriate default handling for reply, forward,
        etc., and

   o    filtering the message list for presentation via limited-
        capability user interfaces (e.g. there is no point in offering
        images when the user is connected by a voice-only telephone
        user interface).

   A problem faced by multimedia messaging systems is that it is not
   always easy to decide the presentation characteristics of a received
   message.  For example:

   o    a message that contains audio and image data:  is this a fax
        message that happens to have some voice commentary, or is it a
        voice message that is accompanied by some supplementary
        diagrams, or is it a fully multimedia message, in which all
        parts are expected to carry equal significance?

   o    a message containing text and audio data:  is this an e-mail
        with an MP3 music attachment, or is it a voice message that
        happens to have been generated with an initial text header for
        the benefit of non-voice-enabled e-mail receivers?

   Thus, the issue of presentation characteristics may be related to
   message media content, but is not the same thing.  The media type
   used in a message is not sufficient to indicate presentation
   characteristics.  One cannot determine a priori which of multiple
   media types to use in a alternative message.  Also what about
   distinguishing traditional e-mail text and SMS messages?  They are
   the same media type, but have different presentation
   characteristics.

  3.2. Some messaging scenarios

   These scenarios are neither comprehensive nor fixed.  For example,
   e-mails being typically text-based do not mean that they cannot
   convey a voice-message.  This very mutability serves to underline
   the desirability of providing some explicit message handling hint.

     3.2.1. Internet e-mail

   Internet e-mail carries textual information.  Sometimes it conveys
   computer application data of arbitrary size.

   Typically, one uses e-mail for non-urgent messages, which the
   recipient will retrieve and process at a time convenient to her.

   The normal device for receiving and processing e-mail messages is
   some kind of personal computer.  Modern personal computers usually
   come with a reasonably large display and an alphanumeric keyboard.
   Audio, video, and printing capabilities are not necessarily
   available.

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   Two parties can use E-mail can for communication between two parties
   (one-to-one), a small number of known parties (one-to-few) or, via
   an e-mail distribution list, between a larger number of unknown
   parties (one-to-many).

   One of the endearing characteristics of e-mail is the way that it
   allows the recipient to forward all or part of a to another party,
   with or without additional comments.  It is quite common for an e-
   mail to contain snippets of content from several previous messages.
   Similar features apply when replying to an e-mail.

     3.2.2. Short text messaging service

   One can use a short text message to convey textual information of
   limited size, typically, up to 160 characters.

   The short text messaging service (SMS) is a facility that has
   evolved for use with mobile telephones, and has an associated per-
   message transmission charge.  People use SMS for relatively urgent
   messages, which the sender wishes the receiver to see and possibly
   respond to within a short time period.

   The normal device for sending and receiving a short text message is
   a mobile telephone with a small character display and a numeric-only
   keyboard.  Personal computers and personal digital assistants (PDAs)
   can also participate in short text messaging.

   Currently, the most common use of short text messages are between
   just two parties (one-to-one).

   Users often send short text messages in isolation, rather than as
   part of a longer exchange.  One use for them is as a prompt or
   invitation to communicate by some more convenient and content-rich
   method, such as a telephone call.

     3.2.3. Facsimile

   People use facsimile to convey image information of moderate size,
   typically a small number of pages.  Sometimes people use facsimile
   for larger documents.

   Facsimile is a facility that usually uses circuit-switched telephone
   circuits, with modest connection-time charges.  Message transfer
   takes place in real-time.  Thus, people often use facsimile for
   moderately urgent.

   The normal device for sending and receiving a facsimile is a self-
   contained scanning and printing device connected to a telephone line
   or a desktop computer.



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   Most facsimiles are between just two parties (one-to-one).  However,
   broadcast facsimile service is between multiple parties (one-to-
   many).

   Most facsimile exchanges are in isolation, rather than as part of a
   longer exchange.  Facsimile data is typically not suitable for
   further processing by computer.

     3.2.4. Voice mail

   People use voice mail to convey audio information, almost
   exclusively human speech.

   Voice mail is a facility that usually uses circuit-switched
   telephone circuits, with modest connection-time charges, often used
   for moderately urgent messages.  A common use for them is as a
   prompt or invitation to communicate by some more convenient method,
   such as a telephone call. In most, but not all cases, the sender of
   a voice message does not want to send a message at all.  Rather,
   they wished to engage in a real-time conversation.

   The normal device for sending and receiving a voice mail is a
   telephone handset.

   Voice messages are usually sent between just two parties (one-to-
   one).

   Voice mail data is not generally suitable for further processing by
   computer.

     3.2.5. Multimedia message

   We define a multimedia message as a message containing more than one
   basic media type (text, image, audio, video, model, application).
   These are the characteristics of a multimedia message.

   In some cases, it is just e-mail with an attachment that a
   multimedia display application presents.  For example, I can send
   you an MP3 of something I recorded in my garage today.

   In other cases, it represents a convergence between two or more of
   the scenarios described above.  For example, a voice message with an
   accompanying diagram or a talking head video message.

   The characteristics will vary somewhat with the intent of the
   sender.  This in turn may affect the user agent or application used
   to create the message.






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  3.3. The goal

   The goal, then, of this document is to describe a simple mechanism
   that provides enough information to allow a receiving user agent to
   make some reasonable decisions about how to present a message.

   The sort of decisions that a receiving agent needs to make include
   the following items.

   o    what icon or class name to display for each message in a list

   o    a default device and/or application to use for presentation of
        the message

   o    whether to try and forward the message into another environment

   It is not a goal for this mechanism to provide detailed handling
   information.  One may apply other techniques to provide more
   detailed handling information.  The mechanism designed here should
   work with, rather than against, these other techniques.


4.   Functional requirements

   o    To identify a message as belonging to one of small number of
        enumerated message classes.

   o    Specify a core set of message classes for all message user
        agents to recognize.

   o    Specify message classes by the originating user's choice of
        authoring tool or simple user interaction.

   o    Incorrect or invalid message labelling must not result in
        failure to transfer or inability to present a message.

   o    Message labeling information has to be interpretable in
        reasonable fashion by many different user agent systems.

   o    The mechanism should be extensible to allow new kinds of
        message to be introduced and labelled.


5.   The Content-Hint

   One method of indicating the interpretation context of the media
   content of a message is to examine the media types in the message.
   However, this requires the UA to scan the entire message before
   making this determination.  This is particularly burdensome for the
   multi-media mail situation, as voice and especially video mail
   objects are quite large.


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   Another method of indicating the primary media content of a message
   is to register a multipart/* MIME subtype.  For example, the VPIM
   Work Group has registered multipart/voice-message to indicate that a
   message is primarily voice mail [4].  However, multipart/voice-
   message is identical in syntax to multipart/mixed.  The only
   difference is that VPIM mail transfer agents and user agents
   recognize that they can perform special handling of the message
   based on it being a voice mail message.

   We wish to avoid scanning the entire message.  In addition, we wish
   to avoid having to create multiple aliases for multipart/mixed every
   time someone identifies a new primary content type.

   Since the content context is an attribute of the entire message, it
   is logical to define a new top-level (RFC 822 [5]) message
   attribute.  To this end, this document introduces the message
   attribute "Content-Hint".

   Content-Hint only serves to identify the content context of the
   message.  It does not provide any indication of content that the UA
   must be capable of delivering.  It does not imply any message
   disposition or delivery notification.  See the companion document,
   Critical Content of Internet Mail [6], for a mechanism to perform
   these tasks.

   Since Content-Hint is only an indicator, goofy situations, such as a
   message marked "voice-message" but without a voice body part, MUST
   NOT generate any error report.


6.   Content-Hint Reference Field

   The Content-Hint reference field is a top-level header inserted by
   the sending UA to indicate the primary content type of the message.

  6.1. Content-Hint Syntax

   The syntax of the Content-Hint field, formatted according to the
   ABNF [7] is as follows.  Note that "Content-Hint" is not case
   sensitive, per RFC 822.

        "Content-Hint" ":" content-hint CRLF

  6.2. content-hint Syntax

   The content-type indicates the primary media content context of the
   message.  This is an IANA registered value.  Current values for
   Content-Hint are as follows.





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        content-hint =  1 *( [ "voice-message"]
                             [ "fax-message" ]
                             [ "video-message" ]
                             [ "sms-message" ]
                             [ "none" ]
                             Extension-type )

        Extension-type = token   ; Defined and registered per Section 8
                       / x-token ; Experimental, private use

        token = <syntax as defined by [8], but not starting with
                 the characters "X-" or "x-">

        x-token = <syntax as defined by [8] for private use>

     6.2.1. voice-message

   The voice-message hint states the message is a voice message, with
   voice messaging semantics.

     6.2.2. fax-message

   The fax-message hint states the message is a facsimile message, with
   facsimile messaging semantics.

     6.2.3. video-message

   The video-message hint states the message is a video message, with
   facsimile messaging sematics.

     6.2.4. sms-message

   The sms-message hint states the message is a short text message
   service (SMS) message, with SMS messaging semantics.

     6.2.5. none

   The none hint states there is no hint for this message.  Clearly, if
   a message has no Content-Hint reference field, none MUST be the
   default value.

7.   Security Considerations

   The intention for this header is to indicate media content context
   only.  One can imagine one creating an "Application" content hint,
   and have a poorly designed user agent blindly execute a mailed
   program.  Don't do that!

   One can envision a denial of service attack by bombing a receiver
   with a message with a Content-hint that doesn't fit the profile of
   the actual body parts.  This is why the receiver MUST consider the


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   Content-hint to be a hint only.  The receiver SHOULD NOT rely on the
   Content-hint exclusively for presentation processing.

8.   IANA Considerations

   NOTE: We won't send in any registrations until it looks like this
   will become a RFC!

   Following the policies outlined in [9], IANA assigns values for
   Content-Hint as Specification Required.

  8.1. Content-Hint Registration

   To: ietf-types@iana.org
   Subject: Registration of New Top-Level Header Field Content-Hint

   Header name:
   Content-Hint

   Required parameters:
   Single 7bit text value

   Parameter value:
   The parameter value specifies the primary media content type for the
   message.

   Security considerations:
   The intention for this header is to indicate media content type
   only. One can imagine one creating an "Application" primary content
   type, and have a poorly designed user agent blindly execute a mailed
   program.

   Published specification:
   draft-ietf-vpim-hint-00.txt

   Applications which use this media type:
   Mail
   VPIM
   FPIM

   Additional information: none

   Person & email address to contact for further information:
   Eric Burger
   e.burger@ieee.org

   Intended usage: COMMON






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   8.2.        Primary Content Type Registrations

     8.2.1. voice-message

   To: ietf-types@iana.org
   Subject: Registration of New Content-Hint type voice-message

   Content-Hint type name:
   voice-message

   Required parameters:
   none

   Optional parameters:
   none

   Encoding considerations:
   none

   Security considerations:
   none

   Interoperability considerations:
   User agents declaring the primary content to be voice-message SHOULD
   conform to VPIMv2.

   Published specification:
   draft-ietf-vpim-hint-00.txt
   RFC 2421, Voice Profile for Internet Mail - version 2

   Applications which use this media type:
   VPIM

   Additional information:
   none

   Person & email address to contact for further information:
   Eric Burger
   e.burger@ieee.org

   Intended usage: COMMON


     8.2.2. fax-message

   To: ietf-types@iana.org
   Subject: Registration of New Content-Hint type fax-message

   Content-Hint type name:
   fax-message



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   Required parameters:
   none

   Optional parameters:
   none

   Encoding considerations:
   none

   Security considerations:
   none

   Interoperability considerations:
   none

   Published specification:
   draft-ietf-vpim-hint-00.txt

   Applications which use this media type:
   FPIM

   Additional information:
   none

   Person & email address to contact for further information:
   Eric Burger
   e.burger@ieee.org

   Intended usage: COMMON


     8.2.3. video-message

   To: ietf-types@iana.org
   Subject: Registration of New Content-Hint type video-message

   Content-Hint type name:
   voice-message

   Required parameters:
   none

   Optional parameters:
   none

   Encoding considerations:
   none

   Security considerations:
   none



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   Interoperability considerations:
   none

   Published specification:
   draft-ietf-vpim-hint-00.txt

   Applications which use this media type:
   VPIM, FPIM

   Additional information:
   none

   Person & email address to contact for further information:
   Eric Burger
   e.burger@ieee.org

   Intended usage: COMMON


     8.2.4. sms-message

   To: ietf-types@iana.org
   Subject: Registration of New Content-Hint type sms-message

   Content-Hint type name:
   sms-message

   Required parameters:
   none

   Optional parameters:
   none

   Encoding considerations:
   none

   Security considerations:
   none

   Interoperability considerations:
   none

   Published specification:
   draft-ietf-vpim-hint-00.txt

   Applications which use this media type:
   VPIM, FPIM

   Additional information:
   none



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   Person & email address to contact for further information:
   Eric Burger
   e.burger@ieee.org

   Intended usage: COMMON


9.   References


   1  Bradner, S., "The Internet Standards Process -- Revision 3", BCP
      9, RFC 2026, October 1996.

   2  Troost, R., Dorner, S., and Moore, K., "Communicating
      Presentation Information in Internet Messages: The Content-
      Disposition Header Field", RFC 2183, New Century Systems,
      QUALCOMM Incorporated, and University of Tennessee, August 1997.

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

   4  Vaudreuil, G. and Parsons, G., "VPIM Voice Message MIME Sub-type
      Registration", RFC 2423, Lucent Technologies and Northern
      Telecom, September 1998.

   5  Crocker, D., "Standard for the Format of ARPA Internet Text
      Messages", STD 11, RFC 822, August 1982.

   6  Burger, E. and Candell, E., "Critical Content of Internet Mail",
      draft-ietf-vpim-cc-00.txt, Work in Progress.

   7  Crocker, D. and Overell, P.(Editors), "Augmented BNF for Syntax
      Specifications: ABNF", RFC 2234, Internet Mail Consortium and
      Demon Internet Ltd., November 1997.

   8  Freed, N. and Borenstein, N., "Multipurpose Internet Mail
      Extensions (MIME) Part One: Format of Internet Message Bodies",
      RFC 2045, Innosoft and First Virtual, November 1996.

   9  Alvestrand, H. and T. Narten, "Guidelines for Writing an IANA
      Considerations Section in RFCs", BCP 26, RFC 2434, October 1998.



10.    Acknowledgments

   Many of the ideas here arose originally from a discussion with Jutta
   Degener.

   We'd also like to thank Keith Moore for helping us tighten-up our
   explanations.


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11.    Author's Addresses

   Eric Burger
   Centigram Communications Corporation
   Maryland Technology Center
   1375 Piccard Dr., MS 150I
   Rockville, MD  20850-4311
   USA

   Phone/Fax: +1 301/212-3320
   Email: e.burger@ieee.org


   Emily Candell
   Comverse Network Systems
   200 Quannapowitt Pkwy.
   Wakefield, MA  01880
   USA

   Phone: +1 781/213-2324
   Email: emily@comversens.com


   Graham Klyne
   Content Technologies Ltd.
   1220 Parkview,
   Arlington Business Park
   Theale
   Reading, RG7 4SA
   United Kingdom.

   Telephone: +44 118 930 1300
   Facsimile: +44 118 930 1301
   E-mail:    GK@ACM.ORG


   Charles Eliot
   Microsoft Corporation
   <<<I need your address here!!!>>>

   Telephone: <Insert Number Here>
   E-Mail: charle@Exchange.Microsoft.com



Full Copyright Statement

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