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Versions: 00 01 02 03 04 05 06 07 08 09 10 rfc4238       Standards Track
       Internet Draft                                       Greg Vaudreuil
       Expires in six months                           Lucent Technologies
                                                             April 8, 2005
                         Voice Message Routing Service
     Status of this Memo
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     Intellectual Property Notice
       By submitting this Internet-Draft, I certify that any applicable
       patent or other IPR claims of which I am aware have been
       disclosed, or will be disclosed, and any of which I become aware
       will be disclosed, in accordance with RFC 3668.
     Copyright Notice
       Copyright (C) The Internet Society (2005).  All Rights Reserved.
       Voice messaging is traditionally addressed using telephone number
       addressing. This document describes two techniques for routing
       voice messages based on a telephone number.  The complete service
       uses the VPIM Directory service to lookup a VPIM email address
       with a telephone number and confirm that the address is both
       valid and the associated with the intended recipient.  However
       this service will take time become widely deployed in the nearest
       term.  This document also describes a basic send-and-pray service
       useful simply to route and deliver messages using only the ENUM
       telephone number resolution service and the existing DNS mail
       routing facilies.
       Internet Draft            VPIM Routing                April 8, 2005
       Please send comments on this document to the VPIM working group
       mailing list <vpim@ietf.org>
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     Table of Contents
     1.   DESIGN GOALS.....................................................4
     2.   THE COMPLETE SERVICE.............................................5
      2.1  Specification of Service "E2U+VPIM:LDAP"........................5
      2.2  VPIM Directory Discovery........................................5
      2.3  Address Query...................................................6
     3.   THE BASIC SERVICE................................................7
      3.1  Specification of Service "E2U+VPIM:Mailto:".....................7
      3.2  Address Construction............................................8
      3.3  Interdomain Message Routing.....................................8
      3.4  Intradomain Message Routing.....................................8
     4.   SECURITY CONSIDERATIONS..........................................10
     5.   IANA CONSIDERATIONS..............................................10
     6.   NORMATIVE REFERENCES.............................................10
     7.   INTELLECTUAL PROPERTY NOTICE.....................................11
     8.   COPYRIGHT NOTICE.................................................11
     9.   AUTHORSÆ ADDRESSES...............................................12
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     1.  Design Goals
       This profile is intended to provide a range of functional
       capabilities for message routing based on one of two mechanisms.
       The most complete service should use the ENUM address resolution
       service to determine the VPIM directory, and then use LDAP to
       retreive the VPIM-specific email address to use for message
       The more basic send-and-pray message service uses only the ENUM
       service and MX records to route the message to the intended
       recipient's domain.  The intelligence to further route the
       message to the intended recipient is placed within the message
       routing system of the recipient's domain.
       The basic mechanism may be used even when there is a VPIM
       directory service available.  The basic service is useful when
       LDAP queries are not available, such as may be the case for
       disconnected mobile terminals or because of firewall or
       information security policies.
       The basic mechanism should facilitate the routing of VPIM
       messages to a suitable internal destination with a minimum of
       configuration.  It is an important goal to avoid any content-
       processing to determine the nature of the message and its
       internal destination.  It should be possible at a minimum to
       establish a simple mail forwarding rule to send all inbound VPIM
       messages to a designated system while facilitating the routing of
       FAX, SMS, or other telephone-addressed messages to other
       potentially different systems.
       It is a goal that the mechanisms outlined in this document be
       extensible for all store-and-forward, telephone-number addressed
       messaging services.
       It is a goal that the VPIM directory discovery and VPIM directory
       query steps occur within the timing constraints for user
       interfaces in PSTN networks.  In general, that constraint can be
       generalized to be a two-second response 95% of the time.
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     2. The Complete Service
       For the complete VPIM message routing service, the sending client
       SHOULD query the VPIM directory for the VPIM-specific email
       address.  The client SHOULD use the ENUM service to retrieve the
       identity of the VPIM Directory to query.  The client should then
       query that server for the email address and any additional
       attributes desired.
     2.1 Specification of Service "E2U+VPIM:LDAP"
          * Service Name: E.164 to VPIM LDAP URL
          * URI Type: "LDAP:"
          * Type: VPIM
          * Subtype: LDAP
          * Functional Specification: See section 3.2 through 3.3
          * Intended Usage: COMMON
          * Author: Greg Vaudreuil (gregv@ieee.org)
          * Security Considerations:
             o Malicious Redirection
                One of the fundamental dangers related to any service
                such as this is that a malicious entry in a resolver's
                database will cause clients to resolve the E.164 into
                the wrong LDAP URL. The possible intent may be to cause
                the client to connect to a rogue LDAP server and
                retrieve (or fail to retrieve) a resource containing
                fraudulent or damaging information.
             o Denial of Service
                By removing the URL to which the E.164 maps, a
                malicious intruder may remove the client's ability to
                access the LDAP directory server.
     2.2 VPIM Directory Discovery
       The VPIM directory server is found by using the ENUM protocol and
       querying for the VPIMDIR service associated with the telephone
       number of the recipient.
       The DNS query name is created as described by [ENUM].  The
       telephone number used for the directory location MAY contain
       additional sub-address information as additional digits.
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                 IN NAPTR  10 10 "U" "E2U+VPIM:LDAP" \
                  "!^.*$!ldap://vdir1.Zcorp.com/telephoneNumber=\1!" .
                 IN NAPTR  10 20 "U" " E2U+VPIM:LDAP" \
                  "!^.*$!ldap://vdir2.Zcorp.com/telephoneNumber=\1!" .
       It is recommended that VPIMDIR servers be deployed in a redundant
       configuration.  NAPTR weight fields provide the ability to give
       two records indicating the same service and preference a
       different weight.  The same weight can be specified for random
       distribution between the two servers. See [NAPTR-1, NAPTR-2,
       NAPTR-3, NAPTR-4]
     2.3 Address Query
       Once the VPIM directory is discovered, the client SHOULD issue a
       LDAP query for the vPIMrFC822Mailbox, that is, the address that
       SHOULD be used as the value for both the RFC822 To: field and the
       SMTP RCPT command. See [VPIMDIR]
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     3. The Basic Service
       The basic service relies upon NAPTR rewrite rules to mechanically
       construct a valid VPIM-specific email address.  In the
       recipient's domain, the constructed address may be further routed
       using intradomain mail routing techniques such as those defined
       in [LASER].
       To facilitate a full range of intradomain routing options, the
       constructed email address indicates that the message is a VPIM
       message.  For ease of processing in the recipient's intradomain
       mail routing system, the indication that the message is a VPIM
       message SHOULD be in the domain name portion.
       Note, that no validation that the constructed address is valid,
       nor that the constructed address corresponds to the intended
       recipient.  Because no capabilities information is provided about
       the recipient, messages sent with this mechaism SHOULD be sent
       using only the media and content types of the VPIM V2 profile.
     3.1 Specification of Service "E2U+VPIM:Mailto:"
          * Service Name: E.164 to VPIM MailTo: URL
          * URI Type: "Mailto:"
          * Type: VPIM
          * Subtype: MAILTO
          * Functional Specification: See section 4.2 through 4.4
          * Intended Usage: COMMON
          * Author: Greg Vaudreuil (gregv@ieee.org)
          * Error Conditions:
             o E.164 number not in the numbering plan
             o E.164 number in the numbering plan, but no URLs exist for
                   that number
             o E2U+VPIM:Mailto Service unavailable
          * Security Considerations:
             o Malicious Redirection
                One of the fundamental dangers related to any service
                such as this is that a malicious entry in a resolver's
                database will cause clients to resolve the E.164 into
                the wrong email URL. The possible intent may be to
                cause the client to send the information to an
                incorrect destination.
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             o Denial of Service
                By removing the URL to which the E.164 maps, a
                malicious intruder may remove the client's ability to
                access the resource.
             o Unsolicited Bulk Email
                The exposure of email addresses through the ENUM
                service provides a bulk mailer access to large numbers
                of email addresses where only the telephone number was
                previously known.
     3.2 Address Construction
       Construct an VPIM email address using the address rewrite rules
       of the NAPTR records associated with the VPIM service.
     3.3 Interdomain Message Routing
       The interdomain routing of a constructed VPIM address is
       mechanically indistinguishable from existing email routing.  No
       changes to the infrastructure are required.  The sending system
       consults the Domain Name System for an MX record corresponding to
       the domain name and forwards the message to the indicated system.
     3.4 Intradomain Message Routing
       Within the recipient's domain, the message may be further routed
       to the appropriate messaging system. Two general mechanisms may
       be used to further route the message to the intended system
       within a network.
             Note: This section is strictly informational.  The
             mechanisms for intradomain routing are an internal matter
             for the domain and do not affect the protocol.  It is only
             necessary that the addresses created by the NAPTR rewrite
             rules have meaning to the domain advertising them.
             However, a convention for the creation and use of such
             address may be useful.
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     3.4.1  Directory-Enabled Routing
       Various proprietary directory mechanisms provide a means for an
       inbound mail router of the recipient's domain to send a message
       to the appropriate internal mail host.  In many cases, the local
       part of the address is used to query for an internal mail
       address.  That internal mail address is substituted for the SMTP
       RCPT address and used to deliver the message to the recipient
       mailbox.  Note that the mailbox does not need to have any
       knowledge of the mechanically-constructed telephone number-based
                   Example address: +12145551212@sp.net
     3.4.2 Service-based Mail Routing
       Alternately, a mail gateway may simply send all voice messages
       into a separate messaging system.  That system may be a single
       voice messaging server or a service-specific gateway into a
       larger telephonenumber-based voice-messaging network.
       Such a mail gateway may be provisioned with a simple rule or
       small set of rules to forward all messages of a given service
       type to a pre-defined server.  This rule would check for the
       service name "VPIM" as a prefix to the constructed domain name to
       reroute messages.
                   Example address: +12145551212@VPIM.sp.net
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     4. Security Considerations
       There is little information disclosed to the sender of a message
       that is not already disclosed using standard email protocols
       beyond the ability to probe, via send-and-fail, the existance of
       a reachable account associated with a telephone number, and via
       the NDN, determine in which domain the account resides.
     4.1 Unsolicited Bulk Email
       However, the use of ENUM records to create routeable email
       addresses from telephone numbers provides bulk-emailers the
       capablities to send email to a large set of recipients where only
       the telephone number is known or where telephone numbers are
     4.2 DNS-based attacks
       Both the complete and basic services rely upon the DNS to provide
       the information necessary to validate a recipient or send a
       message. The message sender is a casual, unauthenticated use of
       the indicated servers, and relies upon the DNS for accurate
       information. If the DNS is compromised, an attacker can redirect
       messages by providing malicious email address or indicate a rogue
       directory with malicious LDAP URL's.  Use of DNS Security
       protocols [DNSSEC] substantially reduce the risk of a domain
       being hijacked.  If the E.164 zone is secured with DNSSEC, then
       the attack is precluded if the client can trust the key used to
       sign the zone. DNS security does not protect against the LDAP
       service independently being compromised.  Further discussion on
       the risk to this LDAP service is provided in [VPIMDIR].
     5. IANA Considerations
       This specification registers the E2U+VPIM and E2U+Voice services
       according to the specifications and guidelines in RFC 3761 [ENUM]
       and the definitions in this document.
     6. References
     6.1 Normative References
     [E164] CCITT Recommendation E.164 (1991), Telephone Network and
        ISDN Operation, Numbering, Routing and Mobile Service -
        Numbering Plan for the ISDN Era.
     [ENUM] Falstrom, P., M. Mealling, "The E.164 to Uniform Resource
        Identifiers (URI) Dynamic Delegation Discovery System (DDDS)
        Application (ENUM)", RFC3761, April 2004 RFC 3761
     [NAPTR-1] Mealling, M., "Dynamic Delegation Discovery System (DDDS)
        Part One: The Comprehensive DDDS", RFC 3401, October 2002.
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     [NAPTR-2] Mealling, M., "Dynamic Delegation Discovery System (DDDS)
        Part Two: The Algorithm", RFC 3402, October 2002.
     [NAPTR-3]  Mealling, M., "Dynamic Delegation Discovery System
        (DDDS) Part Three: The Domain Name System (DNS) Database", RFC
        3403, October 2002.
     [NAPTR-4]  Mealling, M., "Dynamic Delegation Discovery System
        (DDDS) Part Four: The Uniform Resource Identifiers (URI)
        Resolution Application", RFC 3404, October 2002.
      [VPIMDIR] G. Vaudreuil "VPIM Directory Schema", work-in-progress,
        <draft-ietf-vpim-vpimdir-11.txt>, October 12, 2004.
     6.2 Informative References
     [VPIMV2] Vaudreuil, Greg, Parsons, Glen, "Voice Profile for
        Internet Mail, Version 2", RFC 3801, June 2004.
     [DNSSEC] Arends, R., Austein, R., Larson, M., Massey, D. and S.
        Rose,, "DNS Security Introduction and Requirements", <draft-
        ietf-dnsext-dnssec-intro-13.txt>, April 2005.
     7. Intellectual Property Notice
       The IETF takes no position regarding the validity or scope of any
       intellectual property or other rights that might be claimed to
       pertain to the implementation or use of the technology described
       in this document or the extent to which any license under such
       rights might or might not be available; neither does it represent
       that it has made any effort to identify any such rights.
       Information on the IETF's procedures with respect to rights in
       standards-track and standards-related documentation can be found
       in BCP-11.  Copies of claims of rights made available for
       publication and any assurances of licenses to be made available,
       or the result of an attempt made to obtain a general license or
       permission for the use of such proprietary rights by implementors
       or users of this specification can be obtained from the IETF
       The IETF invites any interested party to bring to its attention
       any copyrights, patents or patent applications, or other
       proprietary rights which may cover technology that may be
       required to practice this standard.  Please address the
       information to the IETF Executive Director.
     8. Copyright Notice
       Copyright (C) The Internet Society (2005).  This document is
       subject to the rights, licenses and restrictions contained in BCP
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       78, and except as set forth therein, the authors retain all their
       This document and the information contained herein are provided
     9. AuthorsÆ Addresses
        Gregory M. Vaudreuil
        Lucent Technologies
        9489 Bartgis Ct
        Frederick, MD 21702
        Email: GregV@ieee.org
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