Network Working Group G. Vaudreuil

Network Working Group G. Vaudreuil
Request for Comments: 4237 Lucent Technologies
Category: Standards Track October 2005

Voice Messaging Directory Service

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 (2005).

Abstract

This document provides details of the Voice Profile for Internet Mail
(VPIM) directory service. The service provides the email address of
the recipient that is given a telephone number. It optionally
provides the spoken name of the recipient and the media capabilities
of the recipient.

The VPIM directory Schema provides essential additional attributes to
recreate the voice mail user experience using standardized
directories. This user experience provides, at the time of
addressing, basic assurances that the message will be delivered as
intended. This document combines two earlier documents, one from
Anne Brown and one from Greg Vaudreuil, that define a voice messaging
schema into a single working group submission.

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RFC 4237 Voice Messaging Directory Service October 2005

Table of Contents

1. Scope ...........................................................2
1.1. Design Goals ...............................................2
1.2. Performance Constraints ....................................2
1.3. Scaling Constraints ........................................3
1.4. Reliability Constraints ....................................3
2. The VPIMUser Directory Schema ...................................3
2.1. vPIMTelephoneNumber ........................................4
2.2. vPIMRfc822Mailbox ..........................................4
2.3. vPIMSpokenName .............................................4
2.4. vPIMTextName ...............................................5
2.5. vPIMSupportedAudioMediaTypes ...............................5
2.6. vPIMSupportedMessageContext ................................5
2.7. vPIMExtendedAbsenceStatus ..................................6
2.8. vPIMSupportedUABehaviors ...................................6
2.9. vPIMMaxMessageSize .........................................7
2.10. vPIMSubMailboxes ..........................................8
3. Security Considerations .........................................8
4. IANA Considerations .............................................9
4.1. Object Identifiers .........................................9
4.2. Object Identifier Descriptors ..............................9
5. References .....................................................10
5.1. Normative References ......................................10
5.2. Informative References ....................................10

1. Scope

1.1. Design Goals

The VPIM directory Schema (VPIMDIR) is accessed from outside the
enterprise or service provider domain using the recipient's telephone
number.

1.2. Performance Constraints

Once the identity of the VPIM directory server is known, the email
address, capabilities, and spoken name confirmation information can
be retrieved. This query is expected to use LDAP [LDAP], a
connection-oriented protocol. The protocol transaction includes
multiple packet round-trips to execute the query and retrieval and is
considered to be the highest latency element of the messaging
service. Further, retrieval of the confirmation information may
require the return of a spoken name segment of up to 20kbytes (5
seconds at 4kbytes/second). Over a sufficiently engineered Internet
connection, a 1250 ms response time is believed to be achievable over
the Internet at large.

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RFC 4237 Voice Messaging Directory Service October 2005

1.3. Scaling Constraints

A service provider's namespace is expected to include entries for
tens of millions of subscribers in a flat namespace based on the VPIM
inter-domain address form: telephone_number@domain_name. A large
corporation may have a hundred-thousand entries, while a large
service provider may have tens of millions of entries in a single
domain. It is expected that there will be a single public address
validation service for a given service provider's network. It is
believed that existing directory technology, including horizontal
scalability through replication, will provide sufficient transaction
throughput within the required latency requirements to address this
need. The only fundamental, new requirement this application imposes
on directory servers, beyond similar existing services, is the
ability to return the recipient's spoken name. Preliminary
investigation suggests that storage and retrieval of a spoken name
will not add appreciable latency; however, it will add to the need
for storage capacity.

1.4. Reliability Constraints

DNS provides well-documented redundancy and load-balancing
capabilities for the VPIMDIR. However, the latency requirements to
the end-user may not permit client-side fail-over to a secondary
server and may require the directory server to be implemented as a
high-availability service.

2. The VPIMUser Directory Schema

(IANA-ASSIGNED-OID.1 NAME 'vPIMUser'
SUP 'top'
AUXILIARY
MUST ( vPIMRfc822Mailbox $
vPIMTelephoneNumber )
MAY ( vPIMSpokenName $
vPIMSupportedUABehaviors $
vPIMSupportedAudioMediaTypes $
vPIMSupportedMessageContext $
vPIMTextName $
vPIMExtendedAbsenceStatus $
vPIMMaxMessageSize $
vPIMSubMailboxes ) )

When present, the vPIMUser object contains information useful for
verifying that the dialed telephone number corresponds to the
intended recipient. This object also provides capability information
and mailbox status information useful for guiding composition by the
sender and for setting delivery expectations at sending time.

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2.1. vPIMTelephoneNumber

The attribute vPIMTelephoneNumber is the full E.164 form of the
telephone number [E164], including any sub-addressing portion. The
normal search will be for this attribute.

(IANA-ASSIGNED-OID.2.1 NAME 'vPIMTelephoneNumber'
EQUALITY caseIgnoreMatch
SYNTAX 1.3.6.1.4.1.1466.115.121.1.44{20} )

Example: A North American telephone number with the sub address of 12
would be represented as "+12145551212+12".

Note that vPIMTelephoneNumber is, by default, a multi-valued
attribute. But if an entry has multiple values for this attribute,
those values MUST be distinct from each other in the telephone number
portion. It is expected that each submailbox of a single telephone
number will have its own vPIMUser entry.

The vPIMTelephoneNumber differs from telephoneNumber in [LDAP] in its
support for sub-addressing information and its use as a voice
messaging address. In most cases, these values will be the same.

The telephone number is stored with no parenthesis, spaces, dots, or
hyphens. The leading '+' and the '+' delineating the submailbox are
required markup.

2.2. vPIMRfc822Mailbox

The attribute vPIMRfc822Mailbox stores the inter-domain SMTP address
of the voice mailbox associated with a given telephone number. It is
defined as a distinct attribute to distinguish it from the
rfc822Mailbox attribute that may be used for other purposes.
Although it would be preferable to define vPIMRfc822Mailbox as a
subtype of rfc822Mailbox, it is defined here as an entirely new
attribute because some directory implementations do not support sub-
typing.

(IANA-ASSIGNED-OID.2.2 NAME 'vPIMRfc822Mailbox'
EQUALITY caseIgnoreIA5Match
SYNTAX 1.3.6.1.4.1.1466.115.121.1.26{256} )

2.3. vPIMSpokenName

The vPIMSpokenName attribute is an octet string and MUST be encoded
in 32 kbit/s ADPCM exactly, as defined by [32KADPCM]. vPIMSpokenName
shall contain the spoken name of the user in the voice of the user.
The length of the spoken name segment MUST NOT exceed five seconds.

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Private or additional encoding types are outside the scope of this
version.

(IANA-ASSIGNED-OID.2.3 NAME 'vPIMSpokenName'
EQUALITY octetStringMatch
SYNTAX 1.3.6.1.4.1.1466.115.121.1.40{20000}
SINGLE-VALUE )

2.4. vPIMTextName

The text name is designed to be consistent with the unstructured
text name databases used for calling name delivery service of
caller ID.

(IANA-ASSIGNED-OID.2.4 NAME 'vPIMTextName'
EQUALITY caseIgnoreMatch
SYNTAX 1.3.6.1.4.1.1466.115.121.1.15{20}
SINGLE-VALUE )

2.5. vPIMSupportedAudioMediaTypes

The vPIMSupportedAudioMediaTypes attribute indicates the type(s) of
audio encodings that can be received at the address specified in
vPIMRfc822Mailbox.

(IANA-ASSIGNED-OID.2.5 NAME 'vPIMSupportedAudioMediaTypes'
EQUALITY caseIgnoreIA5Match
SYNTAX 1.3.6.1.4.1.1466.115.121.1.26 )

This is a multi-value attribute. The allowable values for this
attribute are the MIME audio subtypes registered with IANA. Non-
standard and private encoding types must be indicated by prepending
the new type name with either "X-" or "x-".

Because ADPCM is a required format, the audio32kadpcm value must be
listed if this attribute is present.

2.6. vPIMSupportedMessageContext

The message context provides guidance to the sender about the message
contexts the recipient is likely to accept. Message context provides
less precise information about a given recipient's capabilities than
a list of media types. However, given the growing role of media-
conversion gateways, the context indicator provides more useful
guidance to a sender in a "unified messaging" environment.

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(IANA-ASSIGNED-OID.2.6 NAME 'vPIMSupportedMessageContext'
EQUALITY caseIgnoreIA5Match
SYNTAX 1.3.6.1.4.1.1466.115.121.1.26 )

This is a multi-value attribute. The set of valid message context
values is defined in [CONTEXT].

2.7. vPIMExtendedAbsenceStatus

It is common to have an attribute that indicates to the subscriber
whether the recipient is accepting messages during his absence. This
feature -- called "extended absence" -- provides an advisory message
at sending time. It is similar in concept to "vacation notices"
common for textual email, but has its own cultural and operational
nuances.

(IANA-ASSIGNED-OID.2.7 NAME 'vPIMExtendedAbsenceStatus'
EQUALITY caseIgnoreIA5Match
SYNTAX 1.3.6.1.4.1.1466.115.121.1.26
SINGLE-VALUE )

The three values defined are:

"Off", "On", "MsgBlocked"

"Off" indicates that the recipient either does not support extended
absence or has not set such an indicator. "Off" is the default
condition if this attribute is not returned.

"On" indicates that the recipient has set an extended absence
indicator, but the mailbox is still accepting messages for review at
an unspecified future time.

"MsgBlocked" indicates that the recipient has set an extended absence
indicator and the mailbox is currently configured to reject incoming
messages. Messages SHOULD NOT be sent to the recipient if this value
is returned in the vPIMExtendedAbsenceStatus attribute.

2.8. vPIMSupportedUABehaviors

Internet mail does not provide facilities for the sender to know
whether the recipient supports a number of optional features that can
be requested or indicated in the RFC822 headers. This attribute
provides a list of the attributes, considered optional by VPIM and
other vendor-specific attributes, that may be supported by the
recipient. If this attribute is not supported, only those attributes

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listed as mandatory in VPIM are assumed to be supported. Undisclosed
behaviors may be indicated in the RFC822 message; however, there is
no assurance by the receiving system of their support.

(IANA-ASSIGNED-OID.2.8 NAME 'vPIMSupportedUABehaviors'
EQUALITY caseIgnoreIA5Match
SYNTAX 1.3.6.1.4.1.1466.115.121.1.26 )

The following behaviors are defined:

MessageDispositionNotification
MessageSensitivity
MessageImportance

The presence of the MessageDispositionNotification value indicates
that the recipient will send an MDN in response to an MDN request.

MessageSensitivity indicates that the recipient fully supports the
sensitivity indication as defined in VPIM [VPIMV2].

MessageImportance indicates that the recipient fully supports the
importance indication as defined in VPIM [VPIMV2].

These may be further extended without standardization to include
proprietary user interface functional extensions. These proprietary
extension values must be prefixed with an "X-" or "x-".

2.9. vPIMMaxMessageSize

At the time of composition, the message can be checked for acceptable
length using the maximum message size attribute. Maximum message
size is an attribute usually configured by policy of the receiving
system, typically in units of minutes. While ESMTP provides a
mechanism to determine if a message is too long in bytes, it is an
unreliable guide for the composer when multiple encodings, multiple
media, or variable bit-rate encodings are supported.

(IANA-ASSIGNED-OID.2.9 NAME 'vPIMMaxMessageSize'
EQUALITY integerMatch
SYNTAX 1.3.6.1.4.1.1466.115.121.1.27
SINGLE-VALUE )

The attribute indicates the maximum message length in seconds that
the receiving mailbox may receive.

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2.10. vPIMSubMailboxes

This attribute indicates the presence of sub-mailboxes for the
queried telephone number. This information may be used to provide a
post-dial sub-addressing menu to the sender.

(IANA-ASSIGNED-OID.2.10 NAME 'vPIMSubMailboxes'
EQUALITY numericStringMatch
SYNTAX 1.3.6.1.4.1.1466.115.121.1.36{4} )

The allowable values include a list of sub-mailbox numbers with a
numeric range of 1-9999. The user interface may use this information
to prompt the sender to select a sub-mailbox. Spoken names
associated with each sub-mailbox may be individually retrieved by
subsequent queries to the recipient's VPIMDIR service.

3. Security Considerations

The following are known security issues.

1) Service provider customer information is very sensitive,
especially in this time of local phone competition. Service
providers require maximum flexibility to protect this data.
Because of the dense nature of telephone number assignments, this
data is subject to "go fish" queries via repeated LDAP queries to
determine a complete list of current or active messaging
subscribers. To reduce the value of this retrieved data, service
providers may limit disclosure of data that is useful for
telemarketing, such as the textual name, and may disclose only
information useful to the sender, such as the recipient's spoken
name, a data element that is much harder to auto-process.

2) In many countries, there are privacy laws or regulations that
prohibit disclosure of certain kinds of descriptive information
(e.g., text names). Hence, server implementors are encouraged to
support DIT structural rules and name forms [LDAPMODELS] as these
provide a mechanism for administrators to select appropriate
naming attributes for entries. Administrators are encouraged to
use these mechanisms, access controls, and other administrative
controls, which may be available to restrict use of attributes
containing sensitive information when naming entries.

3) The LDAP directory service needs to be secured properly for this
intended use. [LDAPAUTH] describes a number of considerations
that apply in this use. In particular, this service provides
unauthenticated, public access to directory data, and as such, it
is vulnerable to attacks that redirect the query to a rogue server
and offer malicious data.

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4. IANA Considerations

Reference RFC 3383 "Internet Assigned Numbers Authority (IANA)
Considerations for the Lightweight Directory Access Protocol (LDAP)"
[LDAPREG].

4.1. Object Identifiers

IANA has registered an LDAP Object Identifier for use in this
technical specification, according to the following template:

Subject: Request for LDAP OID Registration

Person & email address to contact for further information:

Greg Vaudreuil ([email protected])

Specification: RFC 4237

Author/Change Controller: IESG

Comments:

The assigned OID will be used as a base for identifying a number of
schema elements defined in this document.

4.2. Object Identifier Descriptors

IANA has registered the LDAP Descriptors used in this technical
specification, as detailed in the following template:

Subject: Request for LDAP Descriptor Registration Update

Descriptor (vPIM): see comment

Object Identifier: see comment

Person & email address to contact for further information:

[email protected]

Usage: see comment

Specification: RFC 4237

Author/Change Controller: IESG

Comments:

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The following descriptors have been added:

NAME Type OID
-------------- ---- ------------
vPIMUser O IANA-ASSIGNED-OID.1.1
vPIMRfc822Mailbox A IANA-ASSIGNED-OID.2.1
vPIMTelephoneNumber A IANA-ASSIGNED-OID.2.2
vPIMSpokenName A IANA-ASSIGNED-OID.2.3
vPIMSupportedUABehaviors A IANA-ASSIGNED-OID.2.4
vPIMSupportedAudioMediaTypes A IANA-ASSIGNED-OID.2.5
vPIMSupportedMessageContext A IANA-ASSIGNED-OID.2.6
vPIMTextName A IANA-ASSIGNED-OID.2.7
vPIMExtendedAbsenceStatus A IANA-ASSIGNED-OID.2.8
vPIMMaxMessageSize A IANA-ASSIGNED-OID.2.9
vPIMSubMailboxes A IANA-ASSIGNED-OID.2.10

Where Type A is Attribute and Type O is ObjectClass

5. References

5.1. Normative References

[LDAP] Hodges, J. and R. Morgan, "Lightweight Directory Access
Protocol (v3): Technical Specification", RFC 3377,
September 2002.

[32KADPCM] Vaudreuil, G. and G. Parsons, "Toll Quality Voice - 32
kbit/s Adaptive Differential Pulse Code Modulation
(ADPCM) MIME Sub-type Registration", RFC 3802, June
2004.

[CONTEXT] Burger, E., Candell, E., Eliot, C., and G. Klyne,
"Message Context for Internet Mail", RFC 3458, January
2003.

[E164] CCITT Recommendation E.164 (1991), Telephone Network and
ISDN Operation, Numbering, Routing and Mobile Service -
Numbering Plan for the ISDN Era.

5.2. Informative References

[VPIMV2] Vaudreuil, G. and G. Parsons, "Voice Profile for
Internet Mail - version 2 (VPIMv2)", RFC 3801, June
2004.

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RFC 4237 Voice Messaging Directory Service October 2005

[LDAPREG] Zeilenga, K., "Internet Assigned Numbers Authority
(IANA) Considerations for the Lightweight Directory
Access Protocol (LDAP)", BCP 64, RFC 3383, September
2002.

[LDAPAUTH] Wahl, M., Alvestrand, H., Hodges, J., and R. Morgan,
"Authentication Methods for LDAP", RFC 2829, May 2000.

[LDAPMODELS] Zeilenga, K., "LDAP: Directory Information Models" Work
in Progress, February 2005.

Acknowledgements

This directory schema builds upon the earlier work of Carl Malamud
and Marshall Rose in their TPC.INT remote printing experiment and the
work lead by Anne Brown as part of the EMA voice messaging
committee's directory effort. Anne Brown has provided important
leadership and was a co-author of the original version of this
document.

Bernhard Elliot, working with the TMIA, has provided most of the
organizational impetus to get this project moving, which was a
substantial task given the sometimes slow and bureaucratic nature of
the voice mail industry and regulatory environment.

Thanks to Dave Dudley and the Messaging Alliance (TMA) for their
early work in pioneering a shared directory service for voice
messaging and their continuing efforts to apply that work to this
effort.

Greg White and Jeff Bouis, both of Lucent Technologies, provided
invaluable assistance in reviewing and sanity checking. Countless
errors and inconsistencies were corrected with their diligent review.

As chairman of the VPIM working group, Glenn Parsons has provided
essential support over the many years this document has been in
development.

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Author's Address

Please send comments on this document to the VPIM working group
mailing list <[email protected]>.

Gregory M. Vaudreuil
Lucent Technologies
9489 Bartgis Ct
Frederick, MD 21702

EMail: [email protected]

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RFC 4237 Voice Messaging Directory Service October 2005

Full Copyright Statement

Copyright (C) The Internet Society (2005).

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