Network Working Group                                       J. Livingood
Request for Comments: 5526                  Comcast Cable Communications
Category: Informational                                        P. Pfautz
                                                                   AT&T
                                                             R. Stastny
                                                           Unaffiliated
                                                             April 2009


           The E.164 to Uniform Resource Identifiers (URI)
       Dynamic Delegation Discovery System (DDDS) Application
                       for Infrastructure ENUM

Status of This Memo

  This memo provides information for the Internet community.  It does
  not specify an Internet standard of any kind.  Distribution of this
  memo is unlimited.

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RFC 5526                  Infrastructure ENUM                 April 2009


Abstract

  This document defines the use case for Infrastructure ENUM and
  proposes its implementation as a parallel namespace to "e164.arpa",
  as defined in RFC 3761, as the long-term solution to the problem of
  allowing carriers to provision DNS records for telephone numbers
  independently of those provisioned by end users (number assignees).

Table of Contents

  1. Introduction ....................................................2
  2. Terminology .....................................................3
  3. Zone Apex for Infrastructure ENUM ...............................3
  4. IANA Considerations .............................................3
  5. Security and Privacy Considerations .............................4
  6. Acknowledgements ................................................4
  7. Normative References ............................................4

1.  Introduction

  ENUM (E.164 Number Mapping [1]) is a system that transforms E.164
  numbers [2] into domain names and then uses the DNS (Domain Name
  Service) [3] to discover NAPTR records that specify what services are
  available for a specific domain name.

  ENUM as originally defined was based on the end-user opt-in
  principle.  While this has great potential to foster new services and
  end-user choices in the long term, the current requirements for
  IP-based interconnection of Voice over IP (VoIP) domains require the
  provisioning of large numbers of allocated or served (hosted) numbers
  of a participating service provider, without the need for individual
  users to opt-in.  This way, service providers can provision their own
  ENUM information that is separate, distinct, and likely to be
  different from what an end-user may provision.  This is particularly
  important if Infrastructure ENUM is used for number-portability
  applications, for example, which an end-user would be unlikely
  interested in provisioning but which a service provider would likely
  find essential.

  In addition, while it is possible that service providers could
  mandate that their users opt-into e164.arpa through end-user contract
  terms and conditions, there are substantial downsides to such an
  approach.  Thus, for all these reasons and many others, ENUM for
  end-user provisioning is ill-suited for use by service providers for
  the interconnection of VoIP domains.






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  As VoIP evolves and becomes pervasive, E.164-addressed telephone
  calls need not necessarily traverse the Public Switched Telephone
  Network (PSTN).  Therefore, VoIP service providers have an interest
  in using ENUM on a so-called "Infrastructure" basis in order to keep
  VoIP traffic on IP networks on an end-to-end basis, both within and
  between service provider domains.  This requires a means of
  identifying a VoIP point of interconnection to which calls addressed
  to a given E.164 number may be delivered; Infrastructure ENUM
  provides this means.  Calls that can originate and terminate on IP
  networks, and do not have to traverse the PSTN, will require fewer or
  no points of transcoding, and can also involve additional IP network
  services that are not possible on the PSTN, among other benefits.

  Requirements for Infrastructure ENUM are provided in [4].

2.  Terminology

  The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
  "SHOULD", "SHOULD NOT", "RECOMMENDED",  "MAY", and "OPTIONAL" in this
  document are to be interpreted as described in BCP 14, RFC 2119 [5].

3.  Zone Apex for Infrastructure ENUM

  This document proposes that Infrastructure ENUM be implemented by
  means of a parallel namespace to e164.arpa dedicated to
  Infrastructure ENUM, in a domain that is yet to be determined.  Use
  of a parallel namespace allows carriers and end-users to control
  their ENUM registrations independently, without forcing one to work
  through the other.

  Infrastructure ENUM Tier 2 resource records in the Infrastructure
  ENUM tree will be controlled by the service provider that is
  providing services to a given E.164 number, generally referred to in
  various countries as the "carrier-of-record" (see [4]).  The
  definition of a carrier-of-record for a given E.164 number is a
  national matter or is defined by the entity controlling the numbering
  space.

  See also Section 3, "Requirements for Infrastructure ENUM", of [4].

4.  IANA Considerations

  IANA has created a registry for Enumservices as originally specified
  in RFC 2916 and revised in RFC 3761.  Enumservices registered with
  IANA are valid for Infrastructure ENUM as well as end-user ENUM.






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5.  Security and Privacy Considerations

  This document proposes a new zone apex for ENUM to meet the
  requirements of Infrastructure ENUM.  The over-the-network protocol
  of ENUM is unchanged by the addition of an apex and, as such, the
  Security Considerations of RFC 3761 [1] still apply.  Specific
  considerations related to the security of an Infrastructure ENUM apex
  are given in more detail in Section 4, "Security Considerations", of
  [4].

  Infrastructure ENUM registrations proposed by this document should
  resolve to service provider points-of-interconnection rather than to
  end-user equipment.  Service providers need to take appropriate
  measures to protect their end-user customers from unwanted
  communications as with other types of interconnections.

6.  Acknowledgements

  The authors wish to thank Lawrence Conroy, Patrik Faltstrom, Michael
  Haberler, Otmar Lendl, Steve Lind, Alexander Mayrhofer, Jim Reid, and
  Richard Shockey for their helpful discussions of this document and
  the concept of Infrastructure ENUM.

7.  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, February 2005.

  [3] Mockapetris, P., "Domain names - concepts and facilities", STD
      13, RFC 1034, November 1987.

  [4] Lind, S. and P. Pfautz, "Infrastructure ENUM Requirements", RFC
      5067, November 2007.

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











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RFC 5526                  Infrastructure ENUM                 April 2009


Authors' Addresses

  Jason Livingood
  Comcast Cable Communications
  1500 Market Street
  Philadelphia, PA 19102
  USA

  Phone: +1-215-981-7813
  EMail: [email protected]


  Penn Pfautz
  AT&T
  200 S. Laurel Ave
  Middletown, NJ  07748
  USA

  Phone: +1-732-420-4962
  EMail: [email protected]


  Richard Stastny
  Anzbachgasse 43
  1140 Vienna
  Austria

  Phone: +43-664-420-4100
  EMail: [email protected]






















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