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Network Working Group                                       J. LivingoodRequest for Comments: 5526                  Comcast Cable CommunicationsCategory: Informational                                        P. Pfautz                                                                    AT&T                                                              R. Stastny                                                            Unaffiliated                                                              April 2009The E.164 to Uniform Resource Identifiers (URI)Dynamic Delegation Discovery System (DDDS) Applicationfor Infrastructure ENUMStatus 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.Copyright Notice   Copyright (c) 2009 IETF Trust and the persons identified as the   document authors.  All rights reserved.   This document is subject toBCP 78 and the IETF Trust's Legal   Provisions Relating to IETF Documents in effect on the date of   publication of this document (http://trustee.ietf.org/license-info).   Please review these documents carefully, as they describe your rights   and restrictions with respect to this document.   This document may contain material from IETF Documents or IETF   Contributions published or made publicly available before November   10, 2008.  The person(s) controlling the copyright in some of this   material may not have granted the IETF Trust the right to allow   modifications of such material outside the IETF Standards Process.   Without obtaining an adequate license from the person(s) controlling   the copyright in such materials, this document may not be modified   outside the IETF Standards Process, and derivative works of it may   not be created outside the IETF Standards Process, except to format   it for publication as an RFC or to translate it into languages other   than English.Livingood, et al.            Informational                      [Page 1]

RFC 5526                  Infrastructure ENUM                 April 2009Abstract   This document defines the use case for Infrastructure ENUM and   proposes its implementation as a parallel namespace to "e164.arpa",   as defined inRFC 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 Contents1. Introduction ....................................................22. Terminology .....................................................33. Zone Apex for Infrastructure ENUM ...............................34. IANA Considerations .............................................35. Security and Privacy Considerations .............................46. Acknowledgements ................................................47. Normative References ............................................41.  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.Livingood, et al.            Informational                      [Page 2]

RFC 5526                  Infrastructure ENUM                 April 2009   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 inBCP 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 alsoSection 3, "Requirements for Infrastructure ENUM", of [4].4.  IANA Considerations   IANA has created a registry for Enumservices as originally specified   inRFC 2916 and revised inRFC 3761.  Enumservices registered with   IANA are valid for Infrastructure ENUM as well as end-user ENUM.Livingood, et al.            Informational                      [Page 3]

RFC 5526                  Infrastructure ENUM                 April 20095.  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 ofRFC 3761 [1] still apply.  Specific   considerations related to the security of an Infrastructure ENUM apex   are given in more detail inSection 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",RFC5067, November 2007.   [5] Bradner, S., "Key words for use in RFCs to Indicate Requirement       Levels",BCP 14,RFC 2119, March 1997.Livingood, et al.            Informational                      [Page 4]

RFC 5526                  Infrastructure ENUM                 April 2009Authors' Addresses   Jason Livingood   Comcast Cable Communications   1500 Market Street   Philadelphia, PA 19102   USA   Phone: +1-215-981-7813   EMail: jason_livingood@cable.comcast.com   Penn Pfautz   AT&T   200 S. Laurel Ave   Middletown, NJ  07748   USA   Phone: +1-732-420-4962   EMail: ppfautz@att.com   Richard Stastny   Anzbachgasse 43   1140 Vienna   Austria   Phone: +43-664-420-4100   EMail: richard.stastny@gmail.comLivingood, et al.            Informational                      [Page 5]