Internet Draft
Internet Draft Laile Di Silvestro
Expires in six months Ambos Corporation
Rod Miles
Nortel Networks
Document: <draft-ema-vpimv3-goals-01.txt> March 10, 2000
Goals for Voice Profile for Internet Mail, Version 3
<draft-ema-vpimv3-goals-01.txt>
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
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Table of contents:
1. Abstract
2. Conventions Used in this Document
3. Introduction
4. Goals for Voice Profile for Internet Mail Version 3
4.1 Interoperability
4.1.1 Interoperability with Desktop Email Applications
4.1.2 Interoperability with VPIM v2 and VPIM v3 Voice
Mail Systems
4.1.3 Interoperability with VPIM v3 Unified Messaging
Systems
4.1.4 Interoperability with Traditional Email Systems
4.3 Conformance to Existing Standards
4.4 Backward Compatibility
4.5 Robustness
5. Acknowledgements
6. Author's addresses
7. References
8. Copyright
1. Abstract
This document describes the goals of Voice Profile for Internet Mail
(VPIM), Version 3 and establishes a baseline of desired
functionality against which proposed MIME profiles for Internet
voice messaging can be judged. The primary goal for this version is
to support interoperability with desktop clients. Other goals for
this version of VPIM include backward compatibility, expanded
interoperability with unified messaging systems, and conformance to
Internet standards. This document does not include goals that were
met fully by VPIM version 2 [VPIM2].
Different levels of desirability are indicated throughout the
document.
2. Conventions used in this document
Within this document, different levels of desirability for a MIME
profile for Internet voice messaging are indicated by different
priorities, indicated in {braces}:
{1} There is general agreement that this is a critical
characteristic of any definition of VPIM version 3.
{2} Most believe that this is an important characteristic of VPIM
version 3.
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{3} There is general belief that this is a useful feature of VPIM
version 3, but that other factors might override; a definition that
does not provide this element is acceptable.
In addition, 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 RFC-2119 [REQ].
3. 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 ESMTP [ESMTP] and MIME [MIME1]. With the trend toward
integration of voice mail and email through unified messaging (UM),
it is now necessary to define a new version of VPIM that supports
the needs of desktop applications and unified messaging systems
(including Internet Facsimile [EXFAX]). 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).
This document defines the goals for VPIM version 3 [VPIM3 and IVM].
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 applications is of
particular and important interest to VPIM version 3. This document
will also expand the offerings of service providers by facilitating
access to voice mail from a web client.
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4. Goals for Voice Profile for Internet Mail version 3
VPIM must define the MIME profile and discard rules which will be
used for the interchange of voice mail messages over the Internet,
and must {1} meet the following goals.
4.1 Interoperability
Enhanced interoperability is the primary goal of VPIM version 3. The
profile must {1} enable interoperability between voice mail systems,
unified messaging systems, Internet email servers, and desktop
client applications. Such interoperability will require {1} support
for the new media-agnostic systems, which combine multiple media
types into a single message, as well as support for legacy voice
mail and email systems. It will require {1} features to accommodate
varying capabilities of the voice mail, unified messaging and email
systems. Furthermore, VPIM version 3 must {1} be compatible with
Internet Fax (extended mode) proposed standards and VPIM messages
that are fax messages for both sending and receiving.
To have "interoperability" means that a VPIM version 3 compliant
sender attempting to send to a recipient will not fail because of
incompatibility. It is essential {1} that VPIM version 3 support
interoperability between most of the systems listed below, and
desirable {3} to support all of them:
- Desktop email client applications
- VPIM version 2 and version 3 voice Mail systems
- VPIM version 3 unified messaging systems
- Traditional email servers
VPIM version 3 must also {1} include new functionality to facilitate
access to voice mail messages from desktop applications.
Overall interoperability requires interoperability for all of the
VPIM elements: critical body parts must {1} be preserved, essential
information must be provided in a form that is accessible by the
users {1}, status codes must {1} be understood, and operations that
are standard for each system should {2} be supported.
4.1.1 Interoperability with Desktop Email Applications
Desktop email applications are typically text based. The ability to
listen to, reply to, forward, and generate voice mail messages from
a traditional desktop environment is a relatively new development.
To accommodate current use and future developments in this area,
VPIM version 3 must {1} provide features to support access to voice
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mail messages from the desktop and other email-reading devices. It
would also be desirable {3} for it to support web access to voice
mail from the desktop.
VPIM version 3 should not {2} require desktop email applications to
possess a large amount of processing power, and a base level
implementation must {1} interoperate, even if it does not offer
complex processing. There was a strong desire {2} to select a
mandatory codec. The mandatory codec would be one that is already
widely available on desktops. There was a strong consensus on MSGSM
[MSGSM] being the mandatory codec for the interoperability that
would therefore be provided. For VPIM version 2 interoperability,
{3} there should also be support for the VPIM v2 mandatory codec
[ADPCM and G726].
Any codecs included in the VPIM version 3 specification should {2}
meet the following criteria:
- Availability on desktops: Codecs should {2} be available on
most platforms Windows, UNIX, Mac)
- Source code availability
- Decoding complexity: All codecs must {1} be low complexity
to decode
- Encoding complexity: Some of the codecs must {1} be low
complexity to encode.
- Bit rate: VPIM version 3 must {1} specify a codec with low
bit rate for devices (i.e., wireless) that do not
have much space/bandwidth.
- Voice Over IP support: VPIM version 3 should {2} specify at
least one codec that supports Voice over IP
implementations.
Most desktop email applications and web clients are not capable of
playing raw audio. To support "out-of-the box" playing of voice mail
content, VPIM v3 must {1} support wav encapsulation of audio. To
enable future support of other formats, VPIM version 3 should {2}
provide identification of the codec used without requiring
interpretation of an audio format. VPIM v3 may {3} allow audio
encodings and formats that are not identified in the VPIM version 3
specification to support environments in which the sender is aware
of the optimal encoding and format for the recipient.
Performance and bandwidth issues make it desirable {3} to support
streaming of VPIM version 3 audio to the desktop. VPIM version 3 may
{3} explicitly support formats other than raw audio and wav to
facilitate streaming.
Because most email readers are text/html based and because many
devices are not capable of recording audio content, VPIM v3 must {1}
allow inclusion of text body parts in a voice message. VPIM version
3 should {2} not explicitly prohibit other media types, as long as
critical content is identified and minimal discard rules are
specified.
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To support devices that are not capable of playing audio, VPIM 3
should {2} define an optional way to describe the content of the
message and indicating how the audio content can be accessed.
It is also a desktop requirement {1} to support attachments of any
media type.
4.1.2 Interoperability with VPIM v2 and v3 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 VPIM voice messaging systems and
other compliant systems, VPIM version 3 should {3} have a simple
minimum set of required features that will guarantee
interoperability, as well as provision for additional functionality
that may be supported by more capable systems. Support for this
additional functionality requires {3} a mechanism for identifying
essential content and status codes indicating that a message could
not be delivered due to capability differences. It should {3} also
include a minimum set of discard rules to enable back-down from VPIM
V3 to V2.
Interoperability with VPIM version 2 voice messaging systems is
desirable, but not required. Interoperability should {3} be able to
depend on the receiving system supporting the VPIM version 2
32KADPCM codec [ADPCM and G726] , and should not {3} depend on the
receiving system supporting any additional VPIM version 3 codecs or
audio formats.
To ensure interoperability between VPIM version 2 and version 3
systems, it may {3} be desirable to revise the VPIM version 2
specification to include new status codes and discard rules.
4.1.3 Interoperability with VPIM v3 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.
Most unified messaging systems preserve the notion of a primary
media type with multiple message components that convey essential
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information. Because unified messaging clients have varying
capabilities, these components may have a different media type than
the message. It is also common for unified messaging systems to
permit forwarding and replying to messages of one type as an
attachment to a message of another type.
To accommodate the common functionality of unified messaging
systems, VPIM version 3 must {1} support the inclusion of body parts
of a type other than the primary content type. It must {1} also
support the embedding of VPIM messages as attachments to messages of
another type (such as multipart/mixed), as well as the embedding of
messages of another type as attachments to VPIM messages.
Interoperability with fax and fax messages is a must {1}.
To provide interoperability with systems that cannot handle a
particular content type, VPIM version 3 must {1} provide a mechanism
for identifying essential or primary body parts and may {3} define
media specific status codes and strings to handle non-delivery of
these body parts.
4.1.4 Interoperability with Traditional Email Servers
Traditional email servers are those that support only textual media
as inline content. VPIM version 3 must {1} interoperate consistently
with the current Internet mail environment. If VPIM version 3
messages arrive in users' mailboxes, it is required {1} that the
standard interoperate successfully 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.
4.3 Conformance to Existing Standards
It is the goal of VPIM version 3 to conform as closely as possible
to existing standards while meeting the other goals defined in this
document.
- Restrictions: The profile should {2} impose as few restrictions as
possible to existing Internet mail standards. In particular, it must
{1} support all elements of RFC 822 [RFC822] except those that
prevent the profile from meeting other VPIM version 3 goals.
- Additions: The profile should {2} make as few additions as
possible to existing internet mail standards. It should also {2}
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 VPIM version 3 work group should {2} propose terms
that are already standard or in common use in the desktop
environment.
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4.4 Backward compatibility
It is a goal of this profile to assure backwards compatibility with
VPIM version 2. Where this is not possible, it may be {2} necessary
to clarify version 2. VPIM version 2 has already gone through some
clarifications to aid in interoperability with version 3. VPIM
version 3 should {2} provide and define a minimal set of rules and
status codes [CODES] for handling non-delivery of VPIM v3 messages.
4.5 Robustness
VPIM v3 must {1} be usable in an environment in which there exist
legacy gateways that do not understand MIME. Core features and
critical data must {1} not be lost when messages pass through AMIS
gateways [AMIS-A and AMIS-D]. VPIM version 3 should {2} allow
interoperability with recipient devices and gateways which have
limited buffering capabilities and cannot buffer all header
information.
5. Acknowledgements
The authors gratefully acknowledge the input and feedback
provided by the members of the EMA and IETF VPIM work groups that
has resulted in this revision including: Kevin Chestnut, Bernard
Elliot, Holly Grabowski, Graham Klyne, Larry Masinter, Glenn
Parsons, Eric Schultz, and Greg Vaudreuil.
6. Authors' addresses
Laile L. Di Silvestro
Ambos Corporation
Phone: +1-425-557-2805
Email: laile@mindspring.com
Rod Miles
Nortel Networks
P.O. Box 3511 Station C
Ottawa, ON K1Y 4H7
Canada
Phone: +1-613-768-4087
Fax : +1-616-763-4461
Email: rodmi@nortelnetworks.com
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7. References
[ADPCM] G. Vaudreuil 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 1893,
1/15/1996.
[ESMTP] Klensin, J., Freed, N., Rose, M., Stefferud, E., and D.
Crocker, "SMTP Service Extensions" RFC 1869, United Nations
University, Innosoft International, Inc., Dover Beach Consulting,
Inc., Network Management Associates, Inc., The Branch Office,
November 1995.
[EXFAX] Masinter, L., Wing, D., "Extended Facsimile Using Internet
Mail", RFC 2532, Xerox Corporation, Cisco Systems, March 1999.
[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).
[IVM] McRae, S., "Internet Voice Messaging", Work In Progress,
, October 22, 1999.
[MIME1] N. Freed and N. Borenstein, "Multipurpose Internet Mail
Extensions (MIME) Part One: Format of Internet Message Bodies", RFC
2045, Innosoft, First Virtual, Nov 1996.
[MSGSM] Di Selvestro, L., Hedberg, E., Baribault, G., "Toll
Quality Voice - Microsoft GSM MIME Sub-type Registration", Work In
Progress, , Microsoft Corporation,
April 1, 1999.
[PCM] CCITT, Fascicle III.4 - Recommendation G.711, Geneva, 1972,
"Pulse Code Modulation (PCM) of Voice Frequencies".
[REQ] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
[RFC822] Crocker, D., "Standard for the Format of ARPA Internet
Text Messages", STD 11, RFC 822, UDEL, August 1982.
[VPIM1] Vaudreuil, Greg, "Voice Profile for Internet Mail", RFC
1911, Feb 1996.
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[VPIM2] Vaudreuil, Greg, Parsons, Glen, "Voice Profile for Internet
Mail, Version 2", RFC 2421, September 1998.
[VPIM3] Parsons, Glenn, "Voice Profile for Internet Mail - Version 3
A Simple Approach", Work In Progress, ,
Nortel Networks, June 25, 1999.
8. Full Copyright Statement
Copyright (C) The Internet Society (2000). 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
Internet organizations, except as needed for the purpose of
developing Internet standards in which case the procedures for
copyrights defined in the Internet Standards process must be
followed, or as required to translate it into languages other than
English.
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
"AS IS" basis and THE INTERNET SOCIETY AND THE INTERNET ENGINEERING
TASK FORCE DISCLAIMS 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.
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