ENUM                                                             S. Lind
Internet-Draft                                                 AT&T Labs
Expires: September 23, 2006                                    P. Pfautz
                                                          March 22, 2006

                    Infrastrucure ENUM Requirements

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Copyright Notice

   Copyright (C) The Internet Society (2006).


   This document provides requirements for "infrastructure" or "carrier"
   ENUM (E.164 Number Mapping), defined as the use of RFC 3761
   technology to facilitate interconnection of networks for E.164 number
   addressed services, in particular but not restricted to VoIP (Voice
   over IP.)

Conventions used in this document

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   RFC2119 [1] provides the interpretations for the key words "MUST",
   "RECOMMENDED", "MAY", and "OPTIONAL" found in this document.

Table of Contents

   1.  Infrastructure ENUM . . . . . . . . . . . . . . . . . . . . . . 3
     1.1.  Definition  . . . . . . . . . . . . . . . . . . . . . . . . 3
     1.2.  Background  . . . . . . . . . . . . . . . . . . . . . . . . 3
   2.  Requirements for Infrastructure ENUM  . . . . . . . . . . . . . 4
   3.  Security Considerations . . . . . . . . . . . . . . . . . . . . 5
   4.  IANA Considerations . . . . . . . . . . . . . . . . . . . . . . 5
   5.  Normative References  . . . . . . . . . . . . . . . . . . . . . 5
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . . . 7
   Intellectual Property and Copyright Statements  . . . . . . . . . . 8

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1.  Infrastructure ENUM

1.1.  Definition

   Infrastructure ENUM is defined as the use of the technology in
   RFC3761 [2] by the carrier-of-record for a specific E.164 number [3]
   to map a telephone number into a URI [4] that identifies a specific
   point of interconnection to that service provider's network that
   could enable the originating party to establish communication with
   the associated terminating party.  It is separate from any URIs that
   the end-user, who registers their E.164 number, may wish to associate
   with that E.164 number.

   In User ENUM, the entity or person having the right-to-use in a
   number has the sole discretion about the content of the associated
   domain and thus the zone content.  From a domain registration
   perspective, the end user number assignee is thus the registrant.
   Within the infrastructure ENUM namespace, we use the term "carrier of
   record" for the entity having discretion over the domain and zone
   content and acting as the registrant.  The "carrier of record" will
   typically be a service provider authorized to issue E.164 numbers for
   the provisioning of Public Switched Telephone Network (PSTN) service
   under the authority of a National Regulatory Authority (NRA), but
   generally exhibits one or more of the following properties:

   o it has been assigned one or more national number ranges by an NRA.

   o it has been assigned a number range directly by the International
   Telecommunications Union (ITU), for instance a code under
   "International Networks" (+882) or "Universal Personal
   Telecommunications (UPT)" (+878).

   o it can be the recipient of a number porting operation.

   o it provides a PSTN point-of-interconnect for the number.

   It is understood that definition of carrier or record is ultimately a
   matter for national authorities to determine.

1.2.  Background

   Voice service providers use E.164 numbers currently as their main
   naming and routing vehicle.  Infrastructure ENUM in e164.arpa or
   another publicly available tree allows service providers to link
   Internet based resources such as URIs to E.164 numbers (Note: this is
   the other way round then User ENUM).  This allows service providers
   in addition to interconnecting via the PSTN (or exclusively) to peer
   via IP-based protocols.  Service providers may announce all E.164

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   numbers or number ranges they host, regardless of whether the final
   end-user device is on the Internet, on IP-based closed Next
   Generation Networks (NGNs) or on the PSTN, provided an access (e.g.,
   Session Border Controller (SBC) or gateway) to the destination
   service provider's network is available on the Internet.  There is
   also no guarantee that the originating service provider querying
   infrastructure ENUM is able to access the ingress network element of
   the destination provider's network.  Additional peering and
   accounting agreements requiring authentication may be necessary.  The
   access provided may also be to a shared network of a group of
   providers, resolving the final destination network within the shared

2.  Requirements for Infrastructure ENUM

   1.  Infrastructure ENUM SHALL provide a means for a provider to
       populate DNS resource records (RRs) in a common publicly
       accessible namespace for the E.164 numbering resources for which
       it is the carrier-of-record.
   2.  Queries of infrastructure ENUM fully qualified domain names MUST
       return a result, even if the result is NXDOMAIN.  Queries must
       not be rejected, e.g., based on access control lists.
   3.  Infrastructure ENUM SHALL support RRs providing a URI that can
       identify a point of interconnection for delivery of
       communications addressed to the E.164 number.
   4.  Infrastructure ENUM SHALL support an IRIS [5] capability that
       allows qualified parties to obtain information regarding the
       E.164 numbering resources and the corresponding carrier-of-
       record.  Determination of what information, if any, shall be
       available to which parties is a national matter.
   5.  Implementation of Infrastructure ENUM MUST NOT restrict the
       ability of an end-user, in a competitive environment, to choose a
       Registrar and/or Tier 2 name server provider for end-user ENUM
   6.  Infrastructure ENUM SHALL be implemented under a top level domain
       that can support reliability and performance suitable for PSTN
   7.  Infrastructure ENUM MUST meet all reasonable privacy concerns
       about visibility of information an end user has no control over,
       for example discovery of unlisted numbers, or inadvertent
       disclosure of user identity.
   8.  Proposed implementations of Infrastructure ENUM SHOULD:
       A.  Minimize changes required to existing requirements that are
           part of RFC 3761
       B.  Work with open numbering plans

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       C.  Restrict the need for any additional resolver functionality
           to service provider resolvers.
       D.  Minimize the number of lookups required to obtain as many
           NAPTR (Naming Authority Pointer) records (end-user and
           infrastructure) as possible.
       E.  Minimize the client knowledge of the numbering plan required.
       F.  Maximize synergies with end-user ENUM
       G.  Support interworking with private ENUM trees.

3.  Security Considerations

   Existing security considerations for ENUM detailed in [2] still
   apply.  Note that some registration validation issues concerning end
   user ENUM may not apply to infrastructure ENUM.  Where the Tier 1
   registry is able to identify the provider serving a number e.g.,
   based on industry data for number block assignments and number
   portability, registration might be more easily automated and a
   separate registrar not required.

   Some parties have expressed concern that an infrastructure ENUM could
   compromise end user privacy by making it possible for others to
   identify unlisted or unpublished numbers based on their registration
   in ENUM.  This can be avoided if providers register all of the their
   allocated (as opposed to assigned) numbers.  Unassigned numbers
   should be provisioned to route to the provider's network in the same
   fashion as assigned numbers and only then provide an indication that
   they are unassigned.  In that way, provider registration of a number
   in ENUM provides no more information about status of a number than
   could be obtained by dialing it.

4.  IANA Considerations

   IANA considerations will depend on the architecture ultimately chosen
   to meet the requirements.

5.  Normative References

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

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

   [3]  International Telecommunications Union-T, "The International
        Public Telecommunication Number Plan", Recommendation E.164",

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        May 1997.

   [4]  Berners-Lee, T., Fielding, R., and L. Masinter, "Uniform
        Resource Identifier (URI): Generic Syntax", STD 66, RFC 3986,
        January 2005.

   [5]  Newton, A. and M. Sanz, "IRIS: The Internet Registry Information
        Service (IRIS) Core Protocol", RFC 3981, January 2005.

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Authors' Addresses

   Steven Lind
   AT&T Labs
   180 Park Ave
   Florham Park, NJ  07932-0971

   Email: slind@att.com

   Penn Pfautz
   200 S. Laurel Ave
   Middletown, NJ  07748

   Email: ppfautz@att.com

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