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RFC 3773
Network Working Group E. Candell
Request for Comments: 3773 Comverse
Category: Informational June 2004
High-Level Requirements for Internet Voice Mail
Status of this Memo
This memo provides information for the Internet community. It does
not specify an Internet standard of any kind. Distribution of this
memo is unlimited.
Copyright Notice
Copyright (C) The Internet Society (2004).
Abstract
This document describes the high-level requirements for Internet
Voice Mail (IVM) and establishes a baseline of desired functionality
against which proposed MIME profiles for Internet Voice Messaging can
be judged. IVM is an extension of the Voice Profile for Internet
Mail (VPIM) version 2 designed to support interoperability with
desktop clients. Other goals for this version of VPIM include
expanded interoperability with unified messaging systems, conformance
to Internet standards, and backward compatibility with voice
messaging systems currently running in a VPIM enabled environment.
This document does not include goals that were met fully by VPIM
version 2.
1. 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 SMTP [DRUMSMTP] and MIME [MIME1].
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
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(including, but not limited to, MIME-compliant email clients). With
the trend toward integration of voice mail and email through unified
messaging (UM), it is now necessary to define a profile that supports
the needs of desktop applications and unified messaging systems
(including Internet Facsimile [EXFAX]). This profile is being
referred to as Internet Voice Mail (IVM).
This document defines the goals for Internet Voice Mail. 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 application is of particular
and important interest to IVM. This document will also expand the
offerings of service providers by facilitating access to voice mail
from a web client.
2. Conventions used in this document
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 BCP 14, RFC 2119
[RFC2119].
3. Goals for Internet Voice Mail
3.1. Interoperability
Enhanced interoperability is the primary goal of IVM. The profile
MUST facilitate interoperability between voice mail systems, unified
messaging systems, Internet email servers, and desktop client
applications. Such interoperability MUST support systems which
combine multiple media types in a single message, as well as legacy
voice mail and email systems. It MUST allow the ability to
accommodate varying capabilities of the voice mail, unified
messaging, and email systems. Furthermore, IVM MUST be compatible
with Internet Fax (extended mode) proposed standards and VPIM
messages that contain fax body parts.
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To have "interoperability" means that an IVM compliant sender
attempting to send to a recipient will not fail because of
incompatibility. IVM MUST support interoperability amongst the
systems listed below:
- Desktop Email client applications
- IVM-capable Voice Mail systems
- IVM-capable unified messaging systems
- Traditional email servers
IVM SHOULD also support interoperability with VPIM version 2 Voice
Mail Systems.
IVM MUST include new functionality to facilitate access to voice mail
messages from desktop applications.
Overall interoperability requires interoperability for all message
elements: body parts deemed essential for message validity MUST be
preserved, essential information MUST be provided in a form that is
accessible by the users, status codes [CODES] MUST be understood, and
operations that are standard for each system SHOULD be supported.
3.1.1. Interoperability with Desktop Email Client Applications
Desktop email applications are typically text based. The abilities
to listen to, reply to, forward, and generate voice mail messages
from a traditional desktop environment are relatively new
developments. To accommodate current use and future developments in
this area, IVM MUST provide features to support access to voice mail
messages from the desktop and other email-reading devices. Also, web
access to voicemail SHOULD be supported from the desktop.
IVM SHOULD NOT require desktop email applications to possess a large
amount of processing power, and a base level implementation MUST
interoperate, even if it does not offer complex processing. In order
to support interoperability, at least one mandatory codec MUST be
defined. The mandatory codec(s) SHOULD be widely available on
desktops. For interoperability with VPIM version 2 systems, IVM
applications MAY also support the VPIM v2 mandatory codec, 32KADPCM
[ADPCM and G726-32].
Any codecs included in the IVM specification SHOULD meet the
following criteria:
- Availability on desktops: Codecs SHOULD be available on most
platforms.
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- Source code availability: Source code SHOULD be readily
accessible.
- Decoding complexity: All codecs MUST be low complexity to
decode.
- Encoding complexity: Some of the codecs MUST be low complexity
to encode.
- Bit rate: IVM SHOULD specify a codec with low bit rate for
devices (i.e., wireless) that do not have much space/bandwidth.
- Voice Over IP support: IVM SHOULD specify a codec that supports
Voice over IP implementations.
Voice Content MUST always be contained in an audio/basic content-
type unless the originator is aware that the recipient can handle
other content. To enable future support of other formats, IVM SHOULD
provide identification of the codec used without requiring
interpretation of an audio format. IVM MAY allow audio encodings and
formats that are not identified in the IVM specification to support
environments in which the sender is aware of the optimal encoding and
format for the recipient.
To address performance and bandwidth issues, IVM MAY support
streaming of IVM audio to the desktop. IVM MAY explicitly support
formats other than raw audio to facilitate streaming.
Because most email readers are text/html based and because many
devices are not capable of recording audio content, IVM MUST allow
inclusion of text body parts in a voice message. IVM SHOULD NOT
explicitly prohibit other media types as long as critical content is
identified and minimal discard rules are specified.
To support devices that have applications dedicated to specific media
types or that are not capable of handling specific content, IVM
SHOULD define a way to describe the content of the message,
indicating how the content can be accessed.
Desktop implementation of IVM MUST support attachments of any media
type.
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3.1.2. Interoperability with IVM-capable 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 IVM voice messaging systems and
other compliant systems, IVM SHOULD have a minimum set of required
features that will guarantee interoperability, and also provision for
additional functionality that may be supported by more complex
systems. IVM MUST define a mechanism for identifying essential
content and status codes [CODES] indicating that a message could not
be delivered due to capability differences.
NOTE: IVM SHOULD provide some level of interoperability with VPIM
version 2 voice messaging systems. In order to support minimal
interoperability between IVM and VPIM version 2, IVM systems MAY be
able to receive the VPIM version 2 32KADPCM codec [ADPCM and G726-
32], and MUST gracefully handle the case where a legacy receiving
system does not support the IVM codecs.
3.1.3. Interoperability with IVM-capable 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.
To accommodate the common functionality of unified messaging systems,
IVM MUST support the inclusion of body parts containing different
media types. It MUST also handle messages that contain VPIM messages
as attachments to messages of another type (such as multipart/mixed),
and VPIM messages that contain attachments of another type.
To provide interoperability with systems that cannot handle a
particular content type, IVM MUST provide a mechanism for identifying
critical content and MAY define media specific status codes and
strings to handle non-delivery of these body parts.
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3.1.4. Interoperability with Traditional Email Servers
Traditional email servers are those that support only textual media
as inline content. IVM MUST interoperate consistently with the
current Internet mail environment. If an IVM message arrives in
users' mailboxes, IVM MUST provide a mechanism to interoperate 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.
3.2. Conformance to Existing Standards
It is the goal of IVM to conform as closely as possible to existing
standards while meeting the other goals defined in this document.
- Restrictions: The profile SHOULD impose as few restrictions as
possible to existing Internet mail standards. In particular, it
MUST support all elements of RFC 2822 [DRUMSIMF], except those
that prevent the profile from meeting other IVM goals.
- Additions: The profile SHOULD make as few additions as possible to
existing internet mail standards. It SHOULD 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 IVM work group SHOULD propose terms that are already
standard or in common use in the desktop environment.
3.3. Backward Compatibility
This profile SHOULD provide backward compatibility with VPIM version
2 to the extent that the functionality required to meet the goals of
this profile is not compromised. Where backward compatibility is not
possible, IVM SHOULD provide and define a minimal set of rules and
status codes for handling non-delivery of IVM messages resulting from
interoperability with VPIM version 2 systems and other legacy
systems.
3.4. Robustness
IVM MUST be usable in an environment in which there exist legacy
gateways that do not understand MIME. Core features and critical
data MUST not be lost when messages pass through AMIS gateways
[AMIS-A and AMIS-D]. IVM SHOULD allow interoperability with
recipient devices and gateways that have limited buffering
capabilities and cannot buffer all header information.
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3.5. Security Considerations
To facilitate security, IVM MUST support authenticated and/or
encrypted voice messages. In addition, IVM MUST adhere to the
security issues identified in VPIM v2 [VPIM2] and in the other RFCs
referenced by this document, especially SMTP [DRUMSMTP], Internet
Message Format [DRUMSIMF], and MIME [MIME1].
4. References
4.1. Normative References
[ADPCM] Vaudreuil, G. 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
3463, January 2003.
[DRUMSMTP] Klensin, J., "Simple Mail Transfer Protocol", RFC 2821,
April 2001.
[DRUMSIMF] Resnick, P., "Internet Message Format", RFC 2822, April
2001.
[EXFAX] Masinter, L. and D. Wing, "Extended Facsimile Using
Internet Mail", RFC 2532, March 1999.
[G726-32] 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).
[MIME1] Freed, N. and N. Borenstein, "Multipurpose Internet Mail
Extensions (MIME) Part One: Format of Internet Message
Bodies", RFC 2045, November 1996.
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
[VPIM2] Vaudreuil, G. and G. Parsons, "Voice Profile for Internet
Mail, Version 2", RFC 2421, September 1998.
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4.2. Informative References
[VPIM1] Vaudreuil, Greg, "Voice Profile for Internet Mail", RFC
1911, February 1996.
[VPIM3] Silvestro, L. and R. Miles, "Goals for Voice Profile for
Internet Mail, Version 3", Work in Progress, March 2000.
5. Acknowledgments
This document is the final result of an evolving requirements
document that started with VPIM v3 and evolved into an alternative
specification for a different (i.e., end-to-end instead of server-
to-server) application. The basis for this document was written by
Laile Di Silvestro and Rod Miles [VPIM3].
The author gratefully acknowledges the authors of [VPIM3], and the
input and feedback provided by the members of the EMA and IETF VPIM
work groups.
6. Author's Address
Emily Candell
Comverse
200 Quannapowitt Parkway
Wakefield, MA 01803
Phone: +1-781-213-2324
EMail: emily.candell@comverse.com
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7. Full Copyright Statement
Copyright (C) The Internet Society (2004). This document is subject
to the rights, licenses and restrictions contained in BCP 78, and
except as set forth therein, the authors retain all their rights.
This document and the information contained herein are provided on an
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Acknowledgement
Funding for the RFC Editor function is currently provided by the
Internet Society.
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