VPIM Working Group Stuart McRae
Internet Draft IBM
Document: <draft-ietf-vpim-ivm-05.txt> Glenn Parsons
Category: Standards Track Nortel Networks
February 16, 2004
Internet Voice Messaging
Status of this Memo
This document is an Internet-Draft and is in full conformance with all
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1. Abstract
This document provides for 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.
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 in RFC-2119 [KEYWORDS].
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3. Introduction
People naturally communicate using their voices, and this is
preferable to typing for some forms of communication. By permitting
voicemail to be implemented in an interoperable way on top of Internet
Mail, voice messaging and electronic mail need no longer remain
separate, isolated worlds and users will be able to choose the most
appropriate form of communication. This will also enable new types of
device, 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 which 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 Messaging
(VPIM v2 as defined in RFC 2421 [VPIM2] and being clarified for Draft
Standard in [VPIMV2R2]) when forwarding messages to remote voicemail
systems, but 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, and it is often not reasonable to expect
a VPIM v2 message to be usable by an e-mail recipient. The result is
messages which cannot be processed by the recipient (e.g., because of
the encoding used), or look ugly to the user.
This document therefore proposes a new 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
message. In addition, this document describes features an e-mail
client SHOULD implement to allow recipient's to display voicemail
message 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 is explained how a client MAY provide a
level of interoperability with VPIM v2.
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 [VPIMV2] 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].
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Further information on VPIM and related activities can be found at
http://www.vpim.org or http://www.ema.org/vpim.
4. 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].
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 origination of 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 which 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 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.
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5. 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).
6. Addressing
Any valid Internet Mail address may be used for a voice message.
It is desirable to be able to use and onramp/offramp for delivery of a
voicemail message to a user, which will result in specific addressing
requirements, based on service selectors as 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].
7. Notifications
Delivery Status Notifications MUST be supported. All non-delivery of
messages MUST result in a NDN, if requested [DSN]. 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]).
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8. 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 [VPIMV2].
The VOICE parameter on Content-Disposition from VPIM v2 [VPIMV2]
SHOULD be used to identify the any spoken names or spoken subjects (as
distinct from voice message contents).
The originator's spoken name MAY be included with messages as separate
audio contents, if known, and indicated by the Content-Disposition
VOICE parameter as defined in VPIM v2 [VPIMV2]. If there is a single
recipient for the message, their 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
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 [VPIMV2], 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 MAY MUST MUST
Other MAY MAY MAY MAY
9. Fax Contents
Fax contents SHOULD be carried according to RFC 2532 [IFAX].
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10. 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.
10.1 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 which gets routed to that
desktop will be at least usable by the recipient.
This delivers a level of partial interoperability which 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 messages
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 well 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.
10.2 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 compliant
systems. 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.
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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
which could be applied to this problem, but no standard solution has
yet been defined.
10.3 Gateways
It would be possibly 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 being 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.
11. Security Considerations
It is anticipated that there are no 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].
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12. References
12.1 Normative References
[ADDRESS] Parsons, G., "VPIM Addressing", <draft-ietf-vpim-address-
03.txt>, June 2002, Work in Progress.
[ADPCM] G. Vaudreuil and G. Parsons, "Toll Quality Voice - 32 kbit/s
ADPCM: MIME Sub-type Registration", RFC 2422, September 1998.
Revised by: <draft-ietf-vpim-vpimv2r2-32k-03.txt>, February 2002.
[BEHAVIOUR] Parsons, G., Maruszak, J., "Voice Messaging Client
Behaviour", <draft-ema-vpim-cb-02.txt>, July 2001, Work in Progress.
[CLID] Parsons, G., Maruszak, J., "Calling Line Identification for
VPIM Messages", <draft-ema-vpim-clid-08.txt>, Feb 2004, Work in
Progress.
[CRITICAL] Burger, E., Candell, E., "Critical Content of Internet
Mail" RFC 3459, June 2002.
[DSN] Moore, K., "SMTP Service Extension for Delivery Status
Notifications" RFC 3461, January 2003.
[DSN2] The Multipart/Report Content Type for the Reporting of Mail
System Administrative Messages. G. Vaudreuil. RFC 3262 Jan 2003.
[DSN3] Enhanced Mail System Status Codes. G. Vaudreuil. RFC 3263
January 2003.
[DSN4] An Extensible Message Format for Delivery Status Notifications.
K. Moore, G. Vaudreuil. RFC 3264 January 2003.
[DRUMSMTP] Klensin, J., "Simple Mail Transfer Protocol", RFC 2821 ,
April 2001.
[DRUMSIMF] Resnick, P., "Internet Message Format", RFC 2822, April
2001.
[DUR] G. Parsons and G. Vaudreuil, "Content Duration MIME Header
Definition", RFC 2424, September 1998. Revised by: <draft-ietf-vpim-
vpimv2r2-dur-03.txt>, February 2002, Work in Progress.
[HINT] Burger, E., Candell, E., Eliot, C., Klyne, G. "Message Context
Internet Mail" RFC 3458, June 2002.
[IFAX] Masinter, L., Wing, D. "Extended Facsimile Using Internet
Mail", RFC 2532, March 1999.
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[KEYWORDS] Bradner, S., "Key Words for use in RFCs To Indicate
Requirement Levels", RFC 2119, March 1997.
[MIME1] Freed, N., Borenstein, N., "Multipurpose Internet Mail
Extensions (MIME) Part One: Format of Internet Message Bodies", RFC
2045, November 1996.
[MIME2] N. Freed and N. Borenstein, "Multipurpose Internet Mail
Extensions (MIME) Part Two: Media Types ", RFC 2046, Innosoft, First
Virtual, November 1996.
[MIME5] N. Freed and N. Borenstein, Multipurpose Internet Mail
Extensions (MIME) Part Five: Conformance Criteria and Examples,
RFC 2049, November 1996.
[SELECTOR] Allocchio, C., "Minimal PSTN address format in Internet
Mail", RFC 2303, March 1998.
[SCHEMA] Vaudreuil, G. "Voice Messaging Directory Service",<draft-
ietf-vpim-vpimdir-07.txt> , February 2002, Work in Progress.
[VPIMENUM] Vaudreuil, G. "Voice Message Routing Service", <draft-ietf-
vpim-routing-06.txt> , October 2003, Work in Progress.
[VPIMV2] Vaudreuil, G., Parsons, G., "Voice Profile for Internet
Mail - version 2", RFC 2421, September 1998.
[VPIMV2R2] Vaudreuil, G., Parsons, G., "Voice Profile for Internet
Mail - version 2", <draft-ietf-vpim-vpimv2r2-05.txt>, February 2002,
Work in Progress.
12.2 Informative References
[GOALS] Candell, E., "Goals for Internet Voice Mail", <draft-ietf-
vpim-ivm-goals-03.txt>, April 2001, Work in Progress.
[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.
13. Author's Addresses
Stuart J. McRae
IBM
43 Seymour Gardens
Twickenham, United Kingdom
TW1 3AR
Phone: +44 208 891 1896
Fax: +44 1784 499 112
Email: stuart.mcrae@uk.ibm.com
Glenn W. Parsons
Nortel Networks
P.O. Box 3511, Station C
Ottawa, ON K1Y 4H7
Canada
Phone: +1-613-763-7582
Fax: +1-613-967-5060
Email: gparsons@nortelnetworks.com
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