ENUM -- Telephone Number Mapping                                O. Lendl
Working Group                                                    enum.at
Internet-Draft                                            April 25, 2006
Expires: October 27, 2006


                    The ENUM Branch Location Record
               draft-lendl-enum-branch-location-record-00

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Copyright Notice

   Copyright (C) The Internet Society (2006).

Abstract

   This documents defines the ENUM Branch Location record which is used
   to indicate where the ENUM tree for special ENUM application is
   located.  The primary application for the EBL is to enable a
   temporary solution for the infrastructure ENUM tree.







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Table of Contents

   1.  Introduction . . . . . . . . . . . . . . . . . . . . . . . . .  3

   2.  ENUM Tree Referrals  . . . . . . . . . . . . . . . . . . . . .  3

   3.  The EBL Resource Record  . . . . . . . . . . . . . . . . . . .  3
     3.1   The EBL RDATA Format . . . . . . . . . . . . . . . . . . .  4
     3.2   The EBL Presentation Format  . . . . . . . . . . . . . . .  4

   4.  Examples . . . . . . . . . . . . . . . . . . . . . . . . . . .  4

   5.  Security Considerations  . . . . . . . . . . . . . . . . . . .  4

   6.  IANA Considerations  . . . . . . . . . . . . . . . . . . . . .  5

   7.  Acknowledgements . . . . . . . . . . . . . . . . . . . . . . .  5

   8.  Normative References . . . . . . . . . . . . . . . . . . . . .  5

       Author's Address . . . . . . . . . . . . . . . . . . . . . . .  5

       Intellectual Property and Copyright Statements . . . . . . . .  6




























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1.  Introduction

   ENUM as defined in RFC3761 [4] (User-ENUM) is not well suited for the
   purpose of interconnection by carriers, as can be seen by the use of
   various private tree arrangements based on ENUM mechanisms.

   Using the same E.164 number to domain mapping technique for other
   application under a different apex (instead of e164.arpa) is
   straightforward on the technical side.  Establishing the
   international agreements necessary to delegate the country-code level
   subdomains under the new apex is non-trivial and time-consuming.
   This process is under way [2].

   ENUM Branch Location records as defined by this document can be used
   to quickly introduce new ENUM trees on a per-country opt-in basis by
   storing the layout of new trees in the User-ENUM tree.

   While Infrastructure ENUM is the motivation for the introduction of
   the EBL record, its use it not limited to Infrastructure ENUM.

   More information and motivation can be found in
   draft-ietf-enum-infrastructure-enum-reqs [1] and
   draft-haberler-carrier-enum [3].

2.  ENUM Tree Referrals

   To allow maximum flexibility, the following parameters will be used
   in ENUM tree referrals.

   application: indicating to what kind of application this EBL applies
      to.  In the case of Infrastructure ENUM, this will be
      "infrastructure".
   separator: indicating what label should be inserted into the ENUM
      domain to branch off to the application-specific tree.  This can
      be an empty (zero-length) string.
   position: indicating at what place this what label should be inserted
      into the ENUM domain to branch off to the application-specific
      tree.  A value of 0 means to the right of all digits.
   apex: indicating what domain should replace "e164.arpa" for this
      application.

   The "application" acts as the selector and is stored as the label in
   the DNS.  The other three parameters make up the content of the EBL.

3.  The EBL Resource Record

   The EBL will reside within the country-code level in the User-ENUM
   tree under e164.arpa.



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   The RR type code for the EBL RR is /IANA-ACTION/.

3.1  The EBL RDATA Format

   The RDATA for a EBL RR consists of a position number, separator
   string and an apex domain. <character-string&gt and ;<domain-name>
   refer to the definitions of RFC 1035 [5].

   0  1  2  3  4  5  6  7
   +--+--+--+--+--+--+--+--+
   |       POSITION        |
   +--+--+--+--+--+--+--+--+
   /       SEPARATOR       /
   +--+--+--+--+--+--+--+--+
   /         APEX          /
   +--+--+--+--+--+--+--+--+

   where POSITION is a single byte, SEPARATOR is a <character-string>
   and APEX is a <domain-name>.  Name-compression is not to be used for
   the APEX field.

3.2  The EBL Presentation Format

   The master file format follows the standard rules in RFC 1035.
   POSITION is represented as decimal integer.  SEPARATOR is a quoted
   string, APEX is a domain name and thus does not require quoting.

4.  Examples


   infrastructure.3.4.e164.arpa    IN EBL 2 "i" e164.arpa.
   infrastructure.1.e164.arpa      IN EBL 4 "i" example.com.
   infrastructure.9.4.e164.arpa    IN EBL 0 ""  e164i.arpa.

   This records indicates how the transformation from E.164 number to
   ENUM domains for the application "infrastructure" should be done for
   numbers in country code +43, +1, and +49.  This leads to the
   following mappings:

   +43 15056416            6.1.4.6.5.0.5.i.3.4.e164.arpa
   +1 5551234567           7.6.5.4.3.2.1.i.5.5.5.1.e164.arpa
   +49 891234567           7.6.5.4.3.2.1.9.8.e164i.arpa


5.  Security Considerations

   EBLs are used to direct the ENUM resolvers to other places in the DNS
   for certain applications.  As these EBLs are stored in the User-ENUM



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   tree, these applications therefore depend on the security of the
   User-ENUM tree.

6.  IANA Considerations

   This documents allocates the Resource Records Type field for the EBL
   record.

7.  Acknowledgements

   The author would like to thank Michael Haberler and Richard Stastny
   for their contributions.

8.  Normative References

   [1]  Lind, S. and P. Pfautz, "Infrastrucure ENUM Requirements",
        draft-ietf-enum-infrastructure-enum-reqs-02 (work in progress),
        April 2006.

   [2]  Livingood, J., "The E.164 to Uniform Resource Identifiers (URI)
        Dynamic Delegation Discovery  System (DDDS) Application for
        Infrastructure ENUM", draft-ietf-enum-infrastructure-00 (work in
        progress), April 2006.

   [3]  Haberler, M. and R. Stastny, "Combined User and Carrier ENUM in
        the e164.arpa tree", draft-haberler-carrier-enum-02 (work in
        progress), March 2006.

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

   [5]  Mockapetris, P., "Domain names - implementation and
        specification", STD 13, RFC 1035, November 1987.


Author's Address

   Otmar Lendl
   enum.at GmbH
   Karlsplatz 1/9
   Wien  A-1010
   Austria

   Phone: +43 1 5056416 33
   Email: otmar.lendl@enum.at
   URI:   http://www.enum.at/




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