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Versions: (draft-stastny-iptel-tel-enumdi) 00 01 02 03 04 05 RFC 4759

IPTEL                                                         R. Stastny
Internet-Draft                                                     Oefeg
Expires: September 2, 2005                                    R. Shockey
                                                            Neustar Inc.
                                                               L. Conroy
                                             Siemens Roke Manor Research
                                                           March 1, 2005


           The ENUM Dip Indicator parameter for the "tel" URI
                  <draft-ietf-iptel-tel-enumdi-01.txt>

Status of this Memo

   This document is an Internet-Draft and is subject to all provisions
   of Section 3 of RFC 3667.  By submitting this Internet-Draft, each
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   RFC 3668.

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   This Internet-Draft will expire on September 2, 2005.

Copyright Notice

   Copyright (C) The Internet Society (2005).

Abstract

   This document defines a new parameter "enumdi" in the "tel" Uniform
   Resource Identifier (URI) as defined in RFC3966 to support the
   handling of ENUM queries in SIP proxies, H.323 gatekeepers and other



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   VoIP network elements.  The presence of the "enumdi" parameter
   indicates to the VoIP network element receiving an URI containing an
   E.164 number that an ENUM query as defined in RFC3761 has already
   been performed on the E.164 number indicated by the previous VoIP
   network element.

Table of Contents

   1.  Terminology  . . . . . . . . . . . . . . . . . . . . . . . . .  3
   2.  Introduction . . . . . . . . . . . . . . . . . . . . . . . . .  4
   3.  Formal Syntax  . . . . . . . . . . . . . . . . . . . . . . . .  5
   4.  Normative Rules  . . . . . . . . . . . . . . . . . . . . . . .  6
     4.1   Handling an URI with the "enumdi" parameter  . . . . . . .  6
     4.2   Adding the "enumdi" parameter to URIs  . . . . . . . . . .  6
   5.  Examples . . . . . . . . . . . . . . . . . . . . . . . . . . .  7
   6.  Security Considerations  . . . . . . . . . . . . . . . . . . .  8
   7.  IANA Considerations  . . . . . . . . . . . . . . . . . . . . .  9
   8.  References . . . . . . . . . . . . . . . . . . . . . . . . . . 10
     8.1   Normative References . . . . . . . . . . . . . . . . . . . 10
     8.2   Informative References . . . . . . . . . . . . . . . . . . 10
       Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . 10
       Intellectual Property and Copyright Statements . . . . . . . . 12





























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1.  Terminology

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL
   NOT","SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in
   thisdocument are to be interpreted as described in BCP 14, RFC2119
   [1].













































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2.  Introduction

   VoIP network elements (including UAS and UAC) may be set up in
   different ways to handle E.164 [2] numbers during call setup,
   depending on the capabilities provided.  One common approach is to
   query ENUM as defined in RFC3761 [3].

   If the ENUM query leads to a result, the call is set-up accordingly.
   If the ENUM query does not lead finally to a result, another database
   may be queried and/or the call may finally routed to the PSTN.  In
   doing so, the call may be routed to another VoIP network element.  To
   indicate in signalling to this next VoIP element that an ENUM query
   has already be made for the "tel" URI (specified in RFC3966 [4]), the
   "enumdi" parameter is used, to prevent the next VoIP network element
   from repeating redundant queries.




































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3.  Formal Syntax

   The following syntax specification uses the augmented Backus-Naur
   Form (BNF) as described in RFC2234 [6].

   enumdi                  = *1(enum-dip-indicator)

   enum-dip-indicator      = ";enumdi"

   The "enum-dip-indicator" can appear in the "tel" URI at most once.









































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4.  Normative Rules

   This section discusses how a VoIP network element handles a received
   "tel" URI that contains the "enumdi" parameter or has accessed ENUM
   in e164.arpa for a given E.164 number and needs to add the parameter
   to a "tel" URI.

4.1  Handling an URI with the "enumdi" parameter

   If a VoIP network element receives a "tel" URI containing the
   "enumdi" parameter, the VoIP network element SHOULD NOT retrieve the
   related information for this number from ENUM in e164.arpa even if it
   would normally do so.

   If the received "tel" URI is to be passed to the next network
   element, the VoIP network element MUST pass on the received URI
   containing the "enumdi" parameter unchanged.

4.2  Adding the "enumdi" parameter to URIs

   When a VoIP network element accesses ENUM in e164.arpa for a given
   E.164 number and the result of the query is NXDOMAIN, and the network
   element chooses to pass the call to the next network element by using
   a "tel" URI, the "enumdi" parameter MUST be set.

   When a VoIP network element accesses ENUM in e164.arpa for a given
   E.164 number and either:
   o  the result of the query includes a NAPTR RR containing a "tel" URI
      that has the same E.164 number, or
   o  the result of the query includes a NAPTR RR containing a "tel" URI
      with the "enumdi" parameter set,

   then if that retrieved "tel" URI is chosen to be passed to the next
   network element, the sending VoIP network element MUST pass on the
   retrieved URI with the "enumdi" parameter set.
















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5.  Examples


   a.  A VoIP network element "server.example.com" receives a "tel" URI
       <tel:+441632960038>.  The VoIP network element accesses the DNS
       for NAPTR RR in 8.3.0.0.6.9.2.3.6.1.4.4.e164.arpa., and gets the
       response NXDOMAIN.  The VoIP network element decides to route the
       call to the PSTN via another VoIP network element called
       "gw.example.com".

          It therefore signals to the next VoIP network element with:
             <tel:+441632960038;enumdi>
          or (using the procedures of RFC3261 [5] section 19.1.6):
             <sip:+441632960038;enumdi@gw.example.com;user=phone>.


   b.  A VoIP network element "server.example.com" receives a "tel" URI
       <tel:+441632960038>.  The VoIP network element accesses the DNS
       for NAPTR RR in 8.3.0.0.6.9.2.3.6.1.4.4.e164.arpa., and receives
       the same "tel" URI in reply (i.e.  <tel:+4416232960038>).

       The VoIP network element decides to route the call to the PSTN
       via another VoIP network element "gw.example.com".

          It therefore signals to the next VoIP network element with:
             <tel:+441632960038;enumdi>
          or (using the procedures of RFC3261 [5] section 19.1.6):
             <sip:+441632960038;enumdi@gw.example.com;user=phone>.























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6.  Security Considerations

   In addition to those security implications discussed in the "tel" URI
   [4] specification, there are new security implications associated
   with the defined parameter.

   If the "enumdi" is illegally inserted into the "tel" URI when the
   signaling message carrying the "tel" URI is en route to the
   destination entity, the call may be routed to the PSTN network,
   incurring unexpected charges or the causing a downstream VoIP network
   element to reject the call setup.

   It is less a problem if the "enumdi" is illegally removed.  An
   additional ENUM query may be performed to retrieve the routing number
   information and have the "enumdi" included again.

   It is RECOMMENDED that protocols carrying the "tel" URI ensure
   message integrity during the message transfer between the two
   communicating network elements so as to detect any unauthorized
   changes to the content of the "tel" URI and other information.































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7.  IANA Considerations

   This document requires no IANA actions.
















































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8.  References

8.1  Normative References

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

   [2]  ITU-T, "The International Public Telecommunication Number Plan",
        Recommendation E.164, May 1997.

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

   [4]  Schulzrinne, H., "The tel URI for Telephone Numbers", RFC 3966,
        December 2004.

   [5]  Rosenberg, J., Schulzrinne, H., Camarillo, G., Johnston, A.,
        Peterson, J., Sparks, R., Handley, M. and E. Schooler, "SIP:
        Session Initiation Protocol", RFC 3261, June 2002.

8.2  Informative References

   [6]  Crocker, D. and P. Overell, "Augmented BNF for Syntax
        Specifications: ABNF", RFC 2234, November 1997.

   [7]  Bradner, S., "The Internet Standards Process -- Revision 3",
        RFC 2026, BCP 9, October 1996.

   [8]  Bradner, S., "IETF Rights in Contributions", BCP 78, RFC 3667,
        February 2004.

   [9]  Bradner, S., "Intellectual Property Rights in IETF Technology",
        BCP 79, RFC 3668, February 2004.


Authors' Addresses

   Richard Stastny
   Oefeg
   Postbox 147
   1103 Vienna
   Austria

   Phone: +43-664-420-4100
   Email: Richard.stastny@oefeg.at





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   Richard Shockey
   Neustar Inc.
   46000 Center Oak Plaza
   Sterling, VA  20166
   United States

   Phone: +1-571-434-5651
   Email: richard.shockey@neustar.biz


   Lawrence Conroy
   Siemens Roke Manor Research
   Roke Manor
   Romsey
   United Kingdom

   Phone: +44-1794-833666
   Email: lwc@roke.co.uk

































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   Copyright (C) The Internet Society (2005).  This document is subject
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Acknowledgment

   Funding for the RFC Editor function is currently provided by the
   Internet Society.




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