RFC4415: IANA Registration for Enumservice Voice

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Network Working Group                                        R. Brandner
Request for Comments: 4415                                    Siemens AG
Category: Standards Track                                      L. Conroy
                                             Siemens Roke Manor Research
                                                              R. Stastny
                                                           February 2006

                IANA Registration for Enumservice Voice

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 (2006).


   This document registers the Enumservice "voice" (which has a defined
   subtype "tel"), as per the IANA registration process defined in the
   ENUM specification RFC 3761.  This service indicates that the contact
   held in the generated Uniform Resource Identifier (URI) can be used
   to initiate an interactive voice (audio) call.

Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . . . 2
   2.  Terminology . . . . . . . . . . . . . . . . . . . . . . . . . . 3
   3.  Voice Service Registration  . . . . . . . . . . . . . . . . . . 3
   4.  Example of voice:tel Enumservice  . . . . . . . . . . . . . . . 4
   5.  Security Considerations . . . . . . . . . . . . . . . . . . . . 4
   6.  IANA Considerations . . . . . . . . . . . . . . . . . . . . . . 5
   7.  References  . . . . . . . . . . . . . . . . . . . . . . . . . . 6
       7.1.  Normative References  . . . . . . . . . . . . . . . . . . 6
       7.2.  Informative References  . . . . . . . . . . . . . . . . . 6

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1.  Introduction

   ENUM (E.164 Number Mapping, RFC 3761 [1]) is a system that transforms
   E.164 numbers [2] into domain names and then uses DNS (RFC 1034 [3])
   features such as delegation through NS records, and the use of Naming
   Authority Pointer (NAPTR) records, to look up the communication
   services available for a specific domain name.

   This document registers an Enumservice according to the guidelines
   given in RFC 3761 to be used for provisioning in the services field
   of a NAPTR [4] resource record to indicate what class of
   functionality a given endpoint offers.  The registration is defined
   within the Dynamic Delegation Discovery System (DDDS, [5] [6] [4] [7]
   [8]) hierarchy, for use with the "E2U" DDDS application defined in
   RFC 3761.

   Enumservices have a type and subtype.  This latter is optional, as it
   may be implicit in the service type.  The type defines the kind of
   communication session that can be initiated using the contact
   indicated by the URI generated by the enclosing NAPTR.  In
   telecommunications engineering terms, it reflects the "teleservice".

   The subtype defines the subsystem that is to be used to initiate the
   communication session.  Note that the subtype definition is usually
   associated with the URI scheme that is to be used.

   Both the type and subtype (where present) must be supported for the
   NAPTR to be used by a potential correspondent.

   There are a number of DDDS applications in addition to ENUM (for
   example, see [7] and [8]).  However, an Enumservice indication
   operates only within the context of the "E2U" (ENUM) DDDS

   Whilst the protocol elements that make up ENUM are defined in the
   above documents and in this one, further examples of the use to which
   these may be put are given in other documents, for example, in ETSI
   TS 102 172 [11].

   This document registers the Enumservice "voice" (which has a defined
   subtype "tel"), as per the IANA registration process defined in the
   ENUM specification RFC 3761.  This service indicates that the contact
   held in the generated URI can be used to initiate an interactive
   voice (audio) call.

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2.  Terminology

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   document are to be interpreted as described in BCP 14, RFC 2119 [9].

3.  Voice Service Registration

   Enumservice Name: "voice"

   Enumservice Type: "voice"

   Enumservice Subtype: "tel"

   URI Scheme: 'tel:'

   Functional Specification:

      The kind of communication indicated by this Enumservice is
      "Interactive Voice".  From a protocol perspective, this
      communication is expected to involve bidirectional media streams
      carrying audio data.

      A client may imply that the person controlling population of a
      NAPTR holding this Enumservice indicates his capability to engage
      in an interactive voice session when contacted using the URI
      generated by this NAPTR.

   Security Considerations:

      See Section 5.

   Intended Usage: COMMON


      Rudolf Brandner, Lawrence Conroy, and Richard Stastny (for author
      contact detail, see Authors' Addresses section)

   Any other information the author deems interesting:

      This Enumservice indicates that the person responsible for the
      NAPTR is accessible via the Public Switched Telephone Network
      (PSTN) or Public Land Mobile Network (PLMN) using the value of the
      generated URI.

      The kind of subsystem required to initiate a Voice Enumservice
      with this subtype is a "Dialer".  This is a subsystem that either

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      provides a local connection to the PSTN or PLMN or provides an
      indirect connection to those networks.  The subsystem will use the
      telephone number held in the generated URI to place a voice call.
      The voice call is placed to a network that uses E.164 numbers to
      route calls to an appropriate destination.

      Note that the PSTN/PLMN connection may be indirect.  The end user
      receiving this NAPTR may have a relationship with a Communications
      Service Provider that accepts call initiation requests from that
      subsystem using an IP-based protocol such as SIP or H.323, and
      places the call to the PSTN using a remote gateway service.  In
      this case, the provider either may accept requests using "tel:"
      URIs or has a defined mechanism to convert "tel:" URI values into
      a "protocol-native" form.

      The "tel:" URI value SHOULD be fully qualified (using the "global
      phone number" form of RFC 3966 [10]).  A "local phone number" as
      defined in that document SHOULD NOT be used unless the controller
      of the zone in which the NAPTR appears is sure that it can be
      distinguished unambiguously by all clients that can access the
      resource record and that a call from their network access points
      can be routed to that destination.

4.  Example of voice:tel Enumservice

   The following is an example of the use of the Enumservice registered
   by this document in a NAPTR resource record.

      3.8.0 NAPTR 10 100 "u" "E2U+voice:tel"
         "!^.*$!tel:+441414960000!" .

5.  Security Considerations

   DNS, as used by ENUM, is a global, distributed database.  Thus, any
   information stored there is visible to anyone anonymously.  Whilst
   this is not qualitatively different from publication in a telephone
   directory, it does open the data subjects to having "their"
   information collected automatically without any indication that this
   has been done or by whom.

   Such data harvesting by third parties is often used to generate lists
   of targets for unrequested information; in short, they are used to
   address "spam".  Anyone who uses a Web-archived mailing list is aware
   that the volume of "spam" email sent increases when he or she posts
   to the mailing list; publication of a telephone number in ENUM is no
   different, and may be used for attempts to send "junk faxes" or "junk
   SMS", for example.

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   Many mailing list users have more than one email address and use
   "sacrificial" email accounts when posting to such lists to help
   filter out unrequested emails sent to them.  This is not so easy with
   published telephone numbers; the PSTN E.164 number assignment process
   is much more involved and usually a single E.164 number (or a fixed
   range of numbers) is associated with each PSTN access.  Thus,
   providing a "sacrificial" phone number in any publication is not

   Due to the implications of publishing data on a globally accessible
   database, as a principle the data subjects MUST give their explicit
   informed consent to data being published in ENUM.

   In addition, they should be made aware that, due to storage of such
   data during harvesting by third parties, removal of the data from
   publication will not remove any copies that have been taken; in
   effect, any publication may be permanent.

   However, regulations in many regions will require that the data
   subjects can at any time request that the data be removed from
   publication and that their consent for its publication be explicitly
   confirmed at regular intervals.

   When placing a voice call via the PSTN (or from the Public Land
   Mobile Network), the sender may be charged for this action.  In both
   kinds of networks, calling some numbers is more expensive than
   sending to others; both kinds of networks have "premium rate"
   services that can be charged at a rate considerably more than a
   "normal" call.  As such, it is important that end users be asked to
   confirm placing the call and that the destination number be presented
   to them.  It is the originating user's choice whether or not to place
   a call to this destination number, but the originating user SHOULD be
   shown the destination number so that he or she can make this

   In addition to the specific security considerations given above, all
   security considerations given in RFC 3761 apply, as well as the
   DNS-specific threats covered in RFC 3833 [12].

6.  IANA Considerations

   The IANA has registered the Enumservice "voice" with a single subtype
   "tel" according to the framework defined in RFC 3761.  The current
   document defines this Enumservice and the expected behaviour of

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7.  References

7.1.  Normative References

   [1]   Faltstrom, P. and M. Mealling, "The E.164 to Uniform Resource
         Identifiers (URI) Dynamic Delegation  Discovery System (DDDS)
         Application (ENUM)", RFC 3761, April 2004.

   [2]   ITU-T, "The International Public Telecommunication Number
         Plan", Recommendation E.164, May 1997.

         RFC 1034, November 1987.

   [4]   Mealling, M., "Dynamic Delegation Discovery System (DDDS)  Part
         Three: The Domain Name System (DNS) Database", RFC 3403,
         October 2002.

   [5]   Mealling, M., "Dynamic Delegation Discovery System (DDDS)  Part
         One: The Comprehensive DDDS", RFC 3401, October 2002.

   [6]   Mealling, M., "Dynamic Delegation Discovery System (DDDS)  Part
         Two: The Algorithm", RFC 3402, October 2002.

   [7]   Mealling, M., "Dynamic Delegation Discovery System (DDDS)  Part
         Four: The Uniform Resource Identifiers (URI)", RFC 3404,
         October 2002.

   [8]   Mealling, M., "Dynamic Delegation Discovery System (DDDS)  Part
         Five: URI.ARPA Assignment Procedures", RFC 3405, October 2002.

   [9]   Bradner, S., "Key words for use in RFCs to Indicate Requirement
         Levels", RFC 2119, BCP 14, March 1997.

   [10]  Schulzrinne, H., "The tel URI for Telephone Numbers", RFC 3966,
         December 2004.

7.2.  Informative References

   [11]  ETSI, "Minimum Requirements for Interoperability of ENUM
         Implementations", ETSI TS 102 172, January 2005.

   [12]  Atkins, D. and R. Austein, "Threat Analysis of the Domain Name
         System (DNS)", RFC 3833, August 2004.

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Authors' Addresses

   Rudolf Brandner
   Siemens AG
   Hofmannstr. 51
   81359 Munich

   Phone: +49-89-722-51003
   EMail: rudolf.brandner@siemens.com

   Lawrence Conroy
   Siemens Roke Manor Research
   Roke Manor
   United Kingdom

   Phone: +44-1794-833666
   EMail: lwc@roke.co.uk

   Richard Stastny
   Postbox 147
   1103 Vienna

   Phone: +43-664-420-4100
   EMail: Richard.stastny@oefeg.at

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   Copyright (C) The Internet Society (2006).

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