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  Internet Draft                                               Penn Pfautz
  Document: <draft-pfautz-lind-enum-carrier-00.txt>                   AT&T
  Category: Informational                                       Steve Lind
                                                                      AT&T
                                                              July 7, 2004
  
  
  
  
                         A Combined User/Carrier ENUM
  
                        <draft-pfautz-lind-enum-carrier-00.txt>
  
  
  
  
  Status of this Memo
  
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     This Internet-Draft will expire on January 7, 2005.
  
  Abstract
  
     This document considers how so-called "carrier" or
     "infrastructure" ENUM and "end user" or "public" ENUM can share a
     single Tier 1 registry yet have independent Tier 2 providers. This
     approach allows the common cooperative infrastructure required by
     ENUM to be shared by end users and carriers reducing costs and
     facilitating adoption of ENUM generally. The essence of the
     proposal is to populate the Tier 1 registry with non-terminal
     NAPTRs rather than NS records and use different ENUM service
     fields for carrier and end user records.
  
  
  
  
  
  
  
  
  
  <draft-pfautz-lind-enum-carrier-00  Expires January 2005     1
  
   User/Carrier ENUM                           July 2004
  
  
  1. Introduction
  
     Work on the implementation of ENUM [1] in the ITU [2] and various
     national bodies [3] has tended to assume an end user focus with
     number assignees proactively and uniquely controlling whether
     their numbers are registered into ENUM and being able to select
     the Tier 2 registry that contains the actual NATPR records. As the
     GSTN is seen to evolve towards an application on an underlying IP
     network, carriers have become increasingly interested in using
     ENUM for interconnection, i.e., to provide information, such as a
     SIP address of record, about where interconnecting carriers should
     direct calls to a number which the carrier serves even where the
     customer's ultimate connection to the carrier's network and the
     customer's premise equipment may not be IP based. Also, as VoIP
     carriers proliferate there is an understandable desire to be able
     to connect calls between users of such services without going
     through the GSTN.
  
     These needs have led to proposals for separate "carrier" or
     "infrastructure" ENUM based on a root other than e164.arpa or to
     suggestions that carriers be able to populate NAPTR records in
     their own Tier 2 if the number assignee does not choose to
     register or in the number assignee's Tier 2 if the assignee
     selects a Tier 2 provider other than that used by the carrier by
     which the number is served in the GSTN.
  
     The difficulties with such proposals are that they either require
     construction of a separate parallel tree or complicate
     provisioning and may not support carrier grade service. For
     example, if the number assignee selects a Tier 2 other than the
     one chosen by the carrier that serves their number in the GSTN,
     the carrier would need to find a way to provision its NAPTRs into
     that Tier 2 which may also not meet carrier reliability needs.
     Also, obtaining user consent for registration, while essential for
     applications that may open vulnerabilities to an end user, is
     burdensome where all numbers must be registered for effective
     interconnection of carriers and may be unnecessary where
     registration only involves association of E.164 numbers with
     carrier network elements.
  
  2. Terminology and Abbreviations
  
  
     ENUM   Telephone Number to URI mapping
  
     GSTN   Global Switched Telephone Network
  
     ITU    International Telecommunication Union
  
     NAPTR  Naming Authority Pointer
  
     RFC    Request For Comment
  
     SIP    Session Initiation Protocol
  
     URI    Uniform Resource Identifier
  
     URL    Uniform Resource Locator
  
  
  <draft-pfautz-lind-enum-carrier-00>             Expires January 2005   2
  
   User/Carrier ENUM                           July 2004
  
  
  
  
  3. Proposal
  
     We propose that a common ENUM instantiation that meets both
     carrier and end user needs without duplication of infrastructure
     or restriction of either party's prerogatives is possible.
  
     As commonly discussed today, ENUM implementation is based on a
     tiered architecture with Tier 1 containing NS records that point
     to the Tier 2 which contains the actual NATPR records for a given
     E.164 number. It is here proposed that, instead of NS records,
     Tier 1 be populated with two non-terminal NAPTR records containing
     distinct services parameters, one pointing to the end user Tier 2
     and the other to the carrier Tier 2.
  
     RFC 3761 defines the service field of the ENUM NAPTR record as the
     string "E2U" (for E.164 to URI) plus some enumservice spec, e.g.
     "E2U+sip". ENUM NAPTR records also contain the flag "u" to
     indicate the rule is the last one and that the output is a URI.
  
     We propose there be two classes of service
          "E2U" for end user and,
          "E2C" for carrier
  
  
     populated in NAPTR records at Tier 1. Note that these would not
     include the enumservice spec (e.g., "sip") as NAPTR records for
     specific services would only be provided in the corresponding Tier
     2. At Tier 2 the NAPTR records would include the full enumservice
     spec e.g. ("E2U+sip" or "E2C+sip").
  
     Because the object of the query to Tier 1 is to obtain a domain
     name to query rather than a URI, it is proposed to use the
     Replacement field of the NAPTR rather than the Regexp as described
     in RFC 3403 [4]. Thus records for a number in Tier 1 might look
     like:
  
     $Origin 9.0.3.5.7.6.8.7.9.4.1.e164.arpa.
       IN NAPTR 100 50 "" "E2U"   "" 9.0.3.5.7.6.8.7.9.4.1.joesenum.com
  
       IN NAPTR 100 50 "" "E2C"   "" 9.0.3.5.7.6.8.7.9.4.1.telco.net
  
  
  
  
  5. Security Considerations
  
  
     Existing security considerations for ENUM detailed in [1] still
     apply. Note that some registration validation issues concerning
     end user ENUM may not apply to carrier ENUM. Where the Tier 1
     registry is able to identify the carrier 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.
  
  
  
  
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   User/Carrier ENUM                           July 2004
  
  
  6. IANA Considerations
  
     If the proposal offered is accepted IANA would need to update
     existing ENUMservices registrations to add corresponding E2C
     entries to existing E2U entries.
  
  7. Discussion
  
     The proposal offered here seeks to preserve and leverage the work
     done to implement end user ENUM to support carrier ENUM in a way
     that minimizes duplication of infrastructure, and allow carriers
     and end users to make use of the technology without foreclosing
     the options of either.
  
     It is recognized that there may be instances where end users and
     carriers both populate different NAPTR records for the same
     capabilities (e.g., SIP) in their respective Tier 2s. In such
     cases the client originating the ENUM query will be responsible
     for deciding which records to make use of in initiating
     communication.
  
     Another issue which has prompted discussion of carrier ENUM has
     been concerns from carriers about placing certain network
     information in the publicly accessible DNS. Although the current
     proposal does not specifically address this, the separation of
     Tier 2s may facilitate restrictions on information access.
  
  
  
  
  
  REFERENCES
  
  
     [1]  P. Faltstrom & M. Mealing, "The E.164 to Uniform Resource
          identifiers (URI) Dynamic Delegation Discovery System (DDDS)
          Application (ENUM)," RFC 3761, April 2004.
  
     [2]  International Telecommunications Union, _Supplement 3 to
          Recommendation E.164: Operational and administrative issues
          associated with national implementations of the ENUM
          functions._
  
     [3]  ENUM Forum, _ENUM Forum Specifications for US Implementation
          of ENUM, Document 6000_1 0, March 14, 2003.
  
     [4]  M. Mealing, " Dynamic Delegation Discovery System (DDDS) Part
          Three: The Domain Name system (DNS) Database," RFC 3403,
          October 2002.
  
  
  
  
  
  
  
  
  
  
  
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   User/Carrier ENUM                           July 2004
  
  
  Authors' Addresses
  
  
     Penn Pfautz
     AT&T
     Room E4-3A01
     200 South Laurel Avenue
     Middletown, NJ 07748
     U.S.A.
     Phone: +1-732-420-4962
     Email: ppfautz@att.com
  
  
     Steve Lind
     AT&T
     Room A201
     180 Park Avenue, P.O. BOX 971
     Florham Park, NJ 07932-0971
     U.S.A.
     Phone: +1-973-236-6787
     Email: sdlind@att.com
  
  
  
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