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Versions: (draft-lendl-enum-branch-location-record) 00 01 02 03

ENUM -- Telephone Number Mapping                                O. Lendl
Working Group                                                    enum.at
Internet-Draft                                         November 27, 2006
Intended status: Standards Track
Expires: May 31, 2007


                    The ENUM Branch Location Record
               draft-ietf-enum-branch-location-record-01

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   This Internet-Draft will expire on May 31, 2007.

Copyright Notice

   Copyright (C) The IETF Trust (2006).

Abstract

   This documents defines the ENUM Branch Location record (EBL) which is
   used to indicate where the ENUM tree for special ENUM application is
   located.  The primary application for the EBL record is to provide a
   temporary solution for the Infrastructure ENUM tree location.






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Table of Contents

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

   2.  The generalized ENUM Application  . . . . . . . . . . . . . . . 3

   3.  The EBL Resource Record . . . . . . . . . . . . . . . . . . . . 4
     3.1.  The EBL RDATA Format  . . . . . . . . . . . . . . . . . . . 4
     3.2.  The EBL Presentation Format . . . . . . . . . . . . . . . . 5

   4.  Examples  . . . . . . . . . . . . . . . . . . . . . . . . . . . 5

   5.  Security Considerations . . . . . . . . . . . . . . . . . . . . 6

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

   7.  Acknowledgements  . . . . . . . . . . . . . . . . . . . . . . . 6

   8.  References  . . . . . . . . . . . . . . . . . . . . . . . . . . 6
     8.1.  Normative References  . . . . . . . . . . . . . . . . . . . 6
     8.2.  Informative References  . . . . . . . . . . . . . . . . . . 7

   Author's Address  . . . . . . . . . . . . . . . . . . . . . . . . . 7
   Intellectual Property and Copyright Statements  . . . . . . . . . . 8



























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1.  Introduction

   ENUM as defined in RFC3761 [1] (User-ENUM) is based on the concept of
   a single "golden" tree (e164.arpa) which stores telephone number to
   URI mappings.

   Experience has shown that this single tree is not suitable for all
   applications and usage scenarios.  The rules regarding administrative
   control of domains, opt-in requirements, and delegation hierarchy can
   vary between applications.  See e.g.  Infrastructure ENUM [4].

   While non-terminal NAPTRs (see [2]) can redirect the ENUM resolution
   algorithm to another DNS tree, their semantics are not powerful
   enough to support an integration of Infrastructure ENUM into
   e164.arpa.

   A more generic application-specific redirection mechanism is thus
   needed.

   The ENUM Branch Location (EBL) Record as defined by this document
   contains information which drives a generalized algorithm which
   transforms a telephone number into a domain name.  This extends the
   original algorithm as defined in section 2.4 of RFC3761 [1].


2.  The generalized ENUM Application

   To recap, RFC3761 uses the following algorithm:

   1.  Remove all characters with the exception of the digits.
   2.  Put dots (".") between each digit.
   3.  Reverse the order of the digits.
   4.  Append the string ".e164.arpa" to the end.

   Any application which uses EBL records to generalize the basic ENUM
   algorithm needs to define where EBLs for this application are located
   in the DNS.  The EBL itself contains three parameters which enter
   into the translation algorithm: SEPERATOR, POSITION, and APEX.

   The generalized algorithm to derive the initial FQDN for the NAPTR
   lookup is defined as:

   1.  Apply the application-specific algorithm to translate the
       "Application Unique String" (AUS, the telephone number) to a
       fully qualified domain name.






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   2.  Query the DNS for an EBL record at the location of this FQDN, and
       retrieve the triple (SEPERATOR, POSITION, APEX) from this record.

       If multiple records are present, take the first one.

       If no EBL record was found, use the triple ("", 0, "e164.arpa")
       as default.  This corresponds to the RFC3671 "golden tree".

   3.  Build a list of labels from all digits appearing in the AUS.

   4.  If SEPERATOR is not the empty string, then insert a label
       consisting of SEPERATOR after POSITION labels into this list.  If
       the list was shorter than POSITION elements, then report an
       error.

   5.  Reverse the order of the list.

   6.  Append a label containing APEX at the end of the list.

   7.  Create a single domain name by joining the list together with
       dots (".") between each label.

   Section 4 contains examples.


3.  The EBL Resource Record

   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> and <domain-name> refer
   to the definitions of RFC 1035 [3].

   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.




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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

   This example shows the use of EBL records as defined by the interim
   solution to infrastructure ENUM as defined by
   draft-ietf-enum-combined-01 [5].

   This application defines that the EBL resides at
   "infrastructure".<country-code>.e164.arpa.  Thus for example:

   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 ""  ie164.arpa.

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

   +43 15056416            6.1.4.6.5.0.5.1.i.3.4.e164.arpa
   +1 5551234567           7.6.5.4.3.2.1.i.5.5.5.1.example.com
   +49 891234567           7.6.5.4.3.2.1.9.8.9.4.ie164.arpa

   Here is the list of the intermediate steps for the first example to
   visualize how the algorithm as defined in Section 2 operates on "+43
   15056416":

   1.  According to the I-ENUM spec, retrieve the country-code from the
       number and build a FQDN using "infrastructure", the reversed,
       dot-separated country-code and "e164.arpa", yielding
       "infrastructure.3.4.e164.arpa".

   2.  The EBL lookup for this domain sets SEPERATOR to "i", POSITION to
       "2" and APEX to "e164.arpa".

   3.  The list of labels is ("4","3","1","5","0","5","6","4","1","6").

   4.  The SEPERATOR is "i", POSITION is 2, thus "i" is inserted between
       the second and the third label, yielding:
       ("4","3","i","1","5","0","5","6","4","1","6")





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   5.  Reversing the list: ("6","3","4","6","5","0","5","1","i","3","4")

   6.  Appending APEX:
       ("6","3","4","6","5","0","5","1","i","3","4","e164.arpa")

   7.  Concatenation with dots: "6.3.4.6.5.0.5.1.i.3.4.e164.arpa"


5.  Security Considerations

   EBLs are used to direct ENUM resolvers to other places in the DNS.
   The security of DNS in both the location of the EBLs and wherever
   they point to need to be maintained.

   Applications need to careful when designing their EBL location:
   Information concerning which numbers have been dialed could be leaked
   to the nameserver hosting the EBL records.


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, Richard Stastny,
   Klaus Nieminen, Richard Shockey, and Karsten Fleischhauer for their
   contributions.


8.  References

8.1.  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]  Mealling, M., "Dynamic Delegation Discovery System (DDDS) Part
        Three: The Domain Name System (DNS) Database", RFC 3403,
        October 2002.

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





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8.2.  Informative References

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

   [5]  Haberler, M. and R. Stastny, "Combined User and Infrastructure
        ENUM in the e164.arpa tree", draft-ietf-enum-combined-01 (work
        in progress), October 2006.


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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Full Copyright Statement

   Copyright (C) The IETF Trust (2006).

   This document is subject to the rights, licenses and restrictions
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Acknowledgment

   Funding for the RFC Editor function is provided by the IETF
   Administrative Support Activity (IASA).





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