rfc2421.txt

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Network Working Group                                       G. Vaudreuil
Request for Comments: 2421                           Lucent Technologies
Obsoletes: 1911                                               G. Parsons
Category: Standards Track                               Northern Telecom
                                                          September 1998


              Voice Profile for Internet Mail - version 2

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 (1998).  All Rights Reserved.

Overview

   This document profiles Internet mail for voice messaging.  It
   obsoletes RFC 1911 which describes version 1 of the profile.  A list
   of changes from that document are noted in Appendix F.  As well,
   Appendix A summarizes the protocol profiles of this version of VPIM.

   Please send comments on this document to the EMA VPIM Work Group
   mailing list:  <[e-mail]>

Working Group Summary

   This profile is not the product of an IETF working group, though
   several have reviewed the document.  It is instead the product of the
   VPIM Work Group of the Electronic Messaging Association (EMA).  This
   work group, which has representatives from most major voice mail
   vendors and several email vendors, has held several interoperability
   demonstrations between voice messaging vendors and is currently
   promoting VPIM trials and deployment.











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RFC 2421                        VPIM v2                   September 1998


Table of Contents

   1. ABSTRACT .........................................................3
   2. SCOPE ............................................................3
     2.1 Voice Messaging System Limitations ............................3
     2.2 Design Goals ..................................................4
   3. PROTOCOL RESTRICTIONS ............................................5
   4. VOICE MESSAGE INTERCHANGE FORMAT .................................6
     4.1 Message Addressing Formats ....................................6
     4.2 Message Header Fields .........................................9
     4.3 Voice Message Content Types ..................................15
     4.4 Other Message Content Types ..................................21
     4.5 Forwarded Messages ...........................................23
     4.6 Reply Messages ...............................................23
     4.7 Notification Messages ........................................24
   5. MESSAGE TRANSPORT PROTOCOL ......................................24
     5.1 ESMTP Commands ...............................................25
     5.2 ESMTP Keywords ...............................................27
     5.3 ESMTP Parameters - MAIL FROM .................................28
     5.4 ESMTP Parameters - RCPT TO ...................................29
     5.5 ESMTP - SMTP Downgrading .....................................29
   6. DIRECTORY ADDRESS RESOLUTION ....................................30
   7. IMAP ............................................................30
   8. MANAGEMENT PROTOCOLS ............................................30
     8.1 Network Management ...........................................31
   9. CONFORMANCE REQUIREMENTS ........................................31
   10. SECURITY CONSIDERATIONS ........................................32
     10.1 General Directive ...........................................32
     10.2 Threats and Problems ........................................32
     10.3 Security Techniques .........................................33
   11. REFERENCES .....................................................33
   12. ACKNOWLEDGMENTS ................................................36
   13. AUTHORS' ADDRESSES .............................................36
   14. APPENDIX A - VPIM REQUIREMENTS SUMMARY .........................37
   15. APPENDIX B - EXAMPLE VOICE MESSAGES ............................45
   16. APPENDIX C - EXAMPLE ERROR VOICE PROCESSING ERROR CODES ........50
   17. APPENDIX D - EXAMPLE VOICE PROCESSING DISPOSITION TYPES ........51
   18. APPENDIX E - IANA REGISTRATIONS ................................52
     18.1 vCard EMAIL Type Definition for VPIM ........................52
     18.2 Voice Content-Disposition Parameter Definition ..............52
   19. APPENDIX F - CHANGE HISTORY: RFC 1911 TO THIS DOCUMENT .........54
   20. FULL COPYRIGHT NOTICE ..........................................56









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1. Abstract

   A class of special-purpose computers has evolved to provide voice
   messaging services.  These machines generally interface to a
   telephone switch and provide call answering and voice messaging
   services.  Traditionally, messages sent to a non-local machine are
   transported using analog networking protocols based on DTMF signaling
   and analog voice playback.  As the demand for networking increases,
   there is a need for a standard high-quality digital protocol to
   connect these machines.  The following document is a profile of the
   Internet standard MIME and ESMTP protocols for use as a digital voice
   messaging networking protocol. The profile is referred to as VPIM
   (Voice Profile for Internet Mail) in this document.

   This profile is based on earlier work in the Audio Message
   Interchange Specification (AMIS) group that defined a voice messaging
   protocol based on X.400 technology.  This profile is intended to
   satisfy the user requirements statement from that earlier work with
   the industry standard ESMTP/MIME mail protocol infrastructures
   already used within corporate intranets. This second version of VPIM
   is based on implementation experience and obsoletes RFC 1911 which
   describes version 1 of the profile.

2. Scope

   MIME is the Internet multipurpose, multimedia messaging standard.
   This document explicitly recognizes its capabilities and provides a
   mechanism for the exchange of various messaging technologies,
   primarily voice and facsimile.

   This document specifies a restricted profile of the Internet
   multimedia messaging protocols for use between voice processing
   server platforms.  These platforms have historically been special-
   purpose computers and often do not have the same facilities normally
   associated with a traditional Internet Email-capable computer.  As a
   result, VPIM also specifies additional functionality as it is needed.
   This profile is intended to specify the minimum common set of
   features to allow interworking between compliant systems.

2.1 Voice Messaging System Limitations

   The following are typical limitations of voice messaging platform
   which were considered in creating this baseline profile.

     1) Text messages are not normally received and often cannot be
     easily displayed or viewed.  They can often be processed only via
     text-to-speech or text-to-fax features not currently present in
     many of these machines.



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     2) Voice mail machines usually act as an integrated Message
     Transfer Agent, Message Store and User Agent.  There is no relaying
     of messages, and RFC 822 header fields may have limited use in the
     context of the limited messaging features currently deployed.

     3) Voice mail message stores are generally not capable of
     preserving the full semantics of an Internet message.  As such, use
     of a voice mail machine for gatewaying is not supported.  In
     particular, storage of recipient lists, "Received" lines, and
     "Message-ID" may be limited.

     4) Internet-style distribution/exploder mailing lists are not
     typically supported.  Voice mail machines often implement only
     local alias lists, with error-to-sender and reply-to-sender
     behavior.  Reply-all capabilities using a CC list are not generally
     available.

     5) Error reports must be machine-parsable so that helpful responses
     can be voiced to users whose only access mechanism is a telephone.

     6) The voice mail systems generally limit address entry to 16 or
     fewer numeric characters, and normally do not support alphanumeric
     mailbox names.  Alpha characters are not generally used for mailbox
     identification as they cannot be easily entered from a telephone
     terminal.

2.2 Design Goals

   It is a goal of this profile to make as few restrictions and
   additions to the existing Internet mail protocols as possible while
   satisfying the requirements for interoperability with current
   generation voice messaging systems.  This goal is motivated by the
   desire to increase the accessibility to digital messaging by enabling
   the use of proven existing networking software for rapid development.

   This specification is intended for use on a TCP/IP network; however,
   it is possible to use the SMTP protocol suite over other transport
   protocols.  The necessary protocol parameters for such use is outside
   the scope of this document.

   This profile is intended to be robust enough to be used in an
   environment, such as the global Internet with installed-base gateways
   which do not understand MIME, though typical use is expected to be
   within corporate intranets.  Full functionality, such as reliable
   error messages and binary transport, will require careful selection
   of gateways (e.g., via MX records) to be used as VPIM forwarding
   agents.  Nothing in this document precludes use of general purpose
   MIME email packages to read and compose VPIM messages.  While no



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RFC 2421                        VPIM v2                   September 1998


   special configuration is required to receive VPIM compliant messages,
   some may be required to originate compliant structures.

   It is expected that a VPIM messaging system will be managed by a
   system administrator who can perform TCP/IP network configuration.
   When using facsimile or multiple voice encodings, it is suggested
   that the system administrator maintain a list of the capabilities of
   the networked mail machines to reduce the sending of undeliverable
   messages due to lack of feature support.  Configuration,
   implementation and management of these directory listing capabilities
   are local matters.

3. Protocol Restrictions

   This protocol does not limit the number of recipients per message.
   Where possible, server implementations should not restrict the number
   of recipients in a single message.  It is recognized that no
   implementation supports unlimited recipients, and that the number of
   supported recipients may be quite low.

   This protocol does not limit the maximum message length.
   Implementers should understand that some machines will be unable to
   accept excessively long messages.  A mechanism is defined in the RFC
   1425 SMTP service extensions to declare the maximum message size
   supported.

   The message size indicated in the ESMTP SIZE parameter is in bytes,
   not minutes or seconds.  The number of bytes varies by voice encoding
   format and includes the MIME wrapper overhead.  If the length must be
   known before sending, an approximate translation into minutes or
   seconds can be performed if the voice encoding is known.

   The following sections describe the restrictions and additions to
   Internet mail protocols that are required to be compliant with this
   VPIM v2 profile. Though various SMTP, ESMTP and MIME features are
   described here, the implementer is referred to the relevant RFCs for
   complete details. It is also advisable to check for IETF drafts of
   various Internet Mail specifications that are later than the most
   recent RFCs since, for example, MIME has yet to be published as a
   full IETF Standard. The table in Appendix A summarizes the protocol
   details of this profile.

   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 [REQ].






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4. Voice Message Interchange Format

   The voice message interchange format is a profile of the Internet
   Mail Protocol Suite.  Any Internet Mail message containing the format
   defined in this section is referred to as a VPIM Message in this
   document.  As a result, this document assumes an understanding of the
   Internet Mail specifications.  Specifically, VPIM references
   components from the message format standard for Internet messages
   [RFC822], the Multipurpose Internet Message Extensions [MIME], the
   X.400 gateway specification [X.400], delivery status and message
   disposition notifications [REPORT][DSN][DRPT][STATUS][MDN], and the