Internet Draft Greg Vaudreuil
Expires in six months Lucent Technologies
December 1, 1999
Voice Messaging Directory Service:
Principles of Operation
<draft-vaudreuil-vpimdir-principles-00.txt>
Status of this Memo
This document is an Internet-Draft and is in full conformance with all
provisions of Section 10 of RFC2026.
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Copyright Notice
Copyright (C) The Internet Society (1999). All Rights Reserved.
This Internet-Draft is in conformance with Section 10 of RFC2026.
Overview
This document outlines the principles for the operation of an
experimental telephone number directory service. This service
provides for the resolution of telephone number address to domain name
address, address confirmation and capabilities discovery, and intra-
domain messaging routing. This directory service uses a combination
of DNS and LDAP queries.
The experiment is conducted using voice messaging in the North
American dialing plan as the prototype application.
Please send comments on this document to the author, Greg Vaudreuil
<gregv@lucent.com>.
Internet Draft VPIM Directory December 1, 1999
Working Group Summary
This document is not the product of an IETF working group. It
documents a inter-company voice message interchange experiment
conducted over the Internet as a project of the Telemessaging Industry
Association (TMIA) http://www.tmia.org. The TMIA is a consortium of
large North American wireline and wireless telephone companies.
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Table of Contents
1. ABSTRACT ............................................................4
2. SCOPE ...............................................................5
2.1Design Goals ......................................................5
3. SYSTEM DESCRIPTION ..................................................6
3.1Time Constraints ..................................................6
4. ADDRESS RESOLUTION SERVICE ..........................................7
4.1E164.int Domain ...................................................8
5. INTER-DOMAIN MESSAGE ROUTING ........................................8
6. ADDRESS CONFIRMATION SERVICE ........................................8
6.1Address Validation Server Discovery ...............................9
6.2Address Validation LDAP Query .....................................9
7. INTRA-DOMAIN MESSAGE ROUTING SERVICE ................................9
8. SECURITY CONSIDERATIONS ............................................10
9. REFERENCES .........................................................10
10.ACKNOWLEDGMENTS ....................................................11
11.COPYRIGHT NOTICE ...................................................11
12.AUTHORS' ADDRESSES .................................................12
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1. Abstract
General electronic mail (email) provides a facility for exchanging
messages of seemingly arbitrary content. In common email usage, text
is the primary media with one or more attachments.
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.
Message exchange between these voice-mail only systems can best be
achieved using VPIM Version 2.
Voice messaging uses the ubiquitous telephone as the primary terminal
for access and for the sending of messages. As such, the limitations
of the numeric keypad must be adequately addressed. The following
limitations are addressed by the directory service described in this
document:
1) Telephone numbers are the natural identifiers for messages sent
from a telephone and to a telephone-based recipient. Internet mail on
which VPIM V2 messages are transported use the Domain Name System
identifiers. The directory service must translate between these
addressing systems.
2) Entry of a telephone number is error-prone. While a mis-typed
email address will generally fail to be delivered, a mis-dialed number
may more frequently be delivered to the wrong recipient. Confirmation
that the dialed number corresponds to the intended recipient is
considered an essential part of voice messaging service.
3) Voice terminals are relatively inflexible in the handling of media
and encodings. Spawning a helper application is not feasible.
Coupled with the strong pressure to adopt ever cheaper and more
compact audio encodings, voice messaging requires the ability for the
sender to tailor the composition to the capabilities of the recipient.
4) While telephone numbers uniquely identify a recipient in inter-
domain space, service providers have needs to name or number the
recipient's mailboxes according to more local requirements. A
standard for the mapping between the telephone-number-based inter-
domain form of the email address to an inter-domain form is required
for interoperability between multiple directory and messaging platform
vendors.
5) Telephone-based users have a strong expectation for rapid a
response to addressing actions. While various "delaying" tone or
phrase may extend this (audio hourglass?) time, the accepted normal
maximum interval is two seconds with perceived system failure at five
seconds. The directory system must provide responses within these
tight latency requirements.
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2. Scope
This document is the first of a set that define the experimental voice
messaging directory service. This document discussed design goals and
the principles of operation. Subsequent documents detail the schema
for the DNS and LDAP portions of the service.
2.1 Design Goals
Rapid Deployment through use of existing protocols, products and
infrastructure.
Leverage existing administrative address assignment and authority
delegation hierarchies to accelerate time-to-market.
Provide maximum flexibility for a provider to control sensitive
directory information made available, while ensuring that message can
reliably be exchanged.
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3. System Description
3.1 Performance Constraints
This directory service is latency critical. For the full set of
features, a number of queries must occur within a short time interval,
optimally less than two seconds. The following
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4. Address Resolution Service
The high level directory provides Address Resolution Service (ARS) to
map between telephone numbers and routeable Internet email addresses.
The phone number is the international E.164 form, and the Email
address is the inter-domain form such as 19727332722@voice.SP.net.
The Internet Domain Name System provides an ideal technology for this
directory due to it's fast, hierarchical structure and distributed
administrative model. Earlier experimentation with the TPC.INT remote
printing experiment has shown how the hierarchical assignment of
telephone numbers can be mapped directly to the hierarchy of domains
within the DNS. The ARS directory uses that approach to map any
arbitrary telephone number into a single domain name.
The telephone number data to populate the highest level entries in the
ARS is publicly available. The ITU maintains a list of country codes
and the authorities that manage the sub-structure under countries.
Within North America, the delegation of phone numbers to the NPA/NXX
level is managed by the "Traffic Routing Administration" a cooperative
agreement with Telecordia (http://www.trainfo.com). The delegations
are made available in a quarterly publication called the Local
Exchange Routing Guide (LERG). The LERG is available publicly for a
nominal fee.
Toll free numbers (800 and 888), ported telephone numbers, and sub-
delegation of numbers to enterprises are beyond the scope of this
initial directory experiment.
Local number portability (LNP) does not change the delegation of phone
numbers, but does change their routing. The LNP routing of phone
numbers to carriers is a third-level directory in the hierarchy
managed by the Number Portability Administrative Center (NPAC) managed
under contract by Martian Marrietta (http://www.nanpa.com). While
this data is also publicly available, it does require an agreement to
receive real-time replication from the master database. Due to cost
and time constraints, ported telephone numbers are beyond the scope of
this initial experiment, however, they are very important and any
viable solution must address the need to receive a correct mapping to
a domain name for these number.
Within a given service provider, authority for telephone numbers may
be further sub-assigned to individual customers, either on a number-
by-number, or by telephone number blocks. This delegation is
typically private information maintained by each telco. Successful
exchange of messages using telephone numbers between enterprises
requires that service providers make this information via the
directory service. Similar to the infrastructure for LNP, this effort
is beyond the scope of the initial voice messaging directory
experiment, however, it is a goal to provide the protocol
infrastructure necessary to address this need.
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4.1 E164.int Domain
This document claims the e164.int domain as the root for the telephone
numbering hierarchy. The operating entity for the primary server for
the duration of the experiment is the NANP DNS authority. That
authority has not yet determined, however Lucent Technologies may
assume that responsibility for the duration of the experiment or until
a more suitable entity can be suckered into it.
The North American Numbering Plan (NAMP) subdomain, country code "1"
of the E164 will also be operated on an interim basis by the NANP DNS
authority.
The North American Numbering Plan (NANP) local routing information in
the LERG database maps a telephone number prefix to an Operating
Company Number (OCN). The OCN is the unique identifier of the local
exchange operator that has received the telephone number delegation.
This delegation does not change with LNP.
The primary name server for the NANP will provide domain name service
for the NANP based on a mapping between OCN and the domain name chosen
by the operating company. The NANP DNS authority will maintain the
registration of the domain name to OCN mapping.
Information to Sub-delegate telephone number assignments below a
NPA/NXX level within the NANP will be maintained by the NANP DNS
authority and made generally available as a DNS referral.
5. Inter-domain Message Routing
The high-level directory query provides all the information necessary
to route a message from one service provider to another using the
existing mail routing infrastructure. Mail routers, firewalls, and
redundancy for voice messaging is identical to that deployed for email
routing. This inter-domain mail routing is not discussed in detail in
this proposal, but uses the mail exchange "MX" routing records in DNS
to route a message to one or more appropriate gateways or firewalls.
There is no restriction on the nature of the messages routed to these
gateways. They may be the same as the general-purpose email gateways.
It is up to the receiving system to determine the appropriate
destination with their network for a given message.
6. Address Confirmation Service
Address validation is the directory step whereby one service provider
can inquire of another about the validity of a telephone number for
messaging and to receive spoken name confirmation and a set of
capabilities of the recipient. This is an optional service. A
message sender may send a message to the recipient using the inter-
domain form of the email address determined from the address
resolution service described above. Address confirmation and
capabilities discovery is an additional, higher level of service.
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6.1 Address Validation Server Discovery
The first step of this directory step is to identify the appropriate
directory server of the recipient domain. For this, the DNS provides
an extension record called the service record or SRV. This record
acts like the MX record in providing a list of servers offering a
given service to provide redundancy.
For the voice messaging address validation service, the AVS service
record is defined. (The details are contained within a companion
document). The address validation server is found by querying DNS
with the domain name found in the address resolution step for the SRV
records corresponding with the AVS service. There may be one or more
SRV records for one or more AVS servers for redundancy and load
sharing. It is the responsibility of the querying client to determine
when to query an alternate AVS in the event that the preferred server
is out-of-service given the stringent user interface latency
requirements. It is expected that multiple algorithms will be
explored as part of this experiment.
6.2 Address Validation LDAP Query
The query to the address validation server of the recipient is made to
find the spoken name of the recipient, the status of the mailbox, the
capabilities of the mailbox, and the possible existence of sub-
mailboxes.
The message sender initiates the query and requests information based
on the inter-domain email address of the recipient as found in the
address resolution step. While this query is inherently simple and
LDAP may be seen as overkill, it is useful to leverage the deployment
experience and security work done with LDAP.
The RESCAP work within the IETF may provide an alternative approach,
and if successful may replace this protocol. At this time, the use of
the voice messaging LDAP schema as defined in [VPIMLDAP] is specified
for use in this experiment.
7. Intra-domain Message Routing Service
A common intra-domain message routing challenge is addressed with a
common schema for voice message routing. The ARS directory step
yields an inter-domain email address sufficient to deliver a message
to a given service provider. The service provider must then route the
message within their network to the appropriate platform. To
facilitate maximum interoperability for the duration of this
experiment, a common schema is defined in [VPIMROUTE].
This schema is based in part on the work of the LASER group. As that
work is completed and standardized, it is expected to replace the
limited schema defined in [VPIMROUTE].
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8. Security Considerations
The following are known security issues taken into consideration in
the definition of this directory service.
1) Service provider customer information is very sensitive, especially
in this time of local phone competition. Service providers require
the 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 disclose of data
useful for telemarketing such as the textual name and disclose only
information useful to the sender such as the recipients spoken name, a
data element much harder to auto-process.
2) Registration of an OCN for another carrier may result in messages
being mis-directed to the wrong carrier. As sub-delegations are
implemented, the risk that one the phone numbers delegated to one
enterprise may be mis-pointed at another will increase.
3) Service providers operate in a regulated environment where certian
information about a subscriber must not be disclosed. Voice Messaging
is subject to caller-ID blocking restrictions, restrictions enforced
in the telephony network. No such protection is available on the
Internet. The protection of this data is essential, but is up to the
individual service providers to not disclose this information outside
of their control.
9. References
[MIMEDIR] F. Dawson, T. Howes, & M. Smith, "A MIME Content-Type for
Directory Information", Work In Progress, <draft-ietf-asid-mime-
direct-06.txt>, March 1998
[DNS1] Mockapetris, P., "Domain names - implementation and
specification", RFC1035, Nov 1987.
[DNS2] Mockapetris, P., "Domain names - concepts and facilities", RFC
1034, Nov 1987.
[E164] CCITT Recommendation E.164 (1991), Telephone Network and ISDN
Operation, Numbering, Routing and Mobile Service - Numbering Plan
for the ISDN Era.
[TPC1] Malamud, Carl, Rose, Marshall, "Principles of Operation for the
TPC.INT Subdomain: Remote Printing -- Technical Procedures", RFC
1530, October 1993.
[VPIM2] Vaudreuil, Greg, Parsons, Glen, "Voice Profile for Internet
Mail, Version 2", RFC 2421, September 1998.
[VPIMe164] Vaudreuil, Greg, "Voice Messaging Directory Service:
Principles of Operation", work-in-progress.
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[VPIMARS] Vaudreuil, Greg, "Voice Messaging Directory Service:
DNS-based", work-in-progress.
[VPIMLDAP] Vaudreuil, Greg, " Voice Messaging Directory Service: Address
Validation Schema", work-in-progress.
[SRV] Gulbrandsen, A., Vixie, P., "A DNS RR for specifying the location
of services (DNS SRV)", RFC 2052, October 1996.
10. Acknowledgments
This experimental directory builds upon the earlier work of Carl
Malamud and Marshall Rose in thier TPC.INT remote printing experiment
and the work lead by Anne Brown as part of the EMA voice messaging
committee's directory effort.
Bernhard Elliot working with the TMIA has provided most of the
organizational impetus to get this project moving, a substantial task
given the sometimes slow and bureaucratic nature of the voice mail
business and regulatory environment.
Dave Dudley and the Messaging Aliance (TMA) for thier early work in
pioneering a shared directory service for voice messaging and their
continuing efforts to apply those learnings to this effort.
11. Copyright Notice
"Copyright (C) The Internet Society (1998). 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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12. Authors' Addresses
Gregory M. Vaudreuil
Lucent Technologies,
Communications Application Group
17080 Dallas Parkway
Dallas, TX 75248-1905
United States
Phone/Fax: +1-972-733-2722
Email: GregV@Lucent.Com
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