RFC 5341

Network Working Group                                        C. Jennings
Request for Comments: 5341                                 Cisco Systems
Updates: 3966                                                 V. Gurbani
Category: Standards Track              Bell Laboratories, Alcatel-Lucent
                                                          September 2008

             The Internet Assigned Number Authority (IANA)
        tel Uniform Resource Identifier (URI) Parameter Registry

Status of This Memo

   This document specifies an Internet standards track protocol for the
   Internet community, and requests discussion and suggestions for
   improvements.  Please refer to the current edition of the "Internet
   Official Protocol Standards" (STD 1) for the standardization state
   and status of this protocol.  Distribution of this memo is unlimited.


   This document creates an Internet Assigned Number Authority (IANA)
   registry for tel Uniform Resource Identifier (URI) parameters and
   their values.  It populates the registry with the parameters defined
   in the tel URI specification, along with the parameters in tel URI
   extensions defined for number portability and trunk groups.

Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . . . 2
   2.  Terminology . . . . . . . . . . . . . . . . . . . . . . . . . . 2
   3.  Use of the Registry . . . . . . . . . . . . . . . . . . . . . . 2
   4.  IANA Considerations . . . . . . . . . . . . . . . . . . . . . . 3
     4.1.  tel URI Parameters Registry . . . . . . . . . . . . . . . . 3
     4.2.  Registration Policy for tel URI Parameters  . . . . . . . . 4
   5.  Security Considerations . . . . . . . . . . . . . . . . . . . . 5
   6.  Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . . 5
   7.  References  . . . . . . . . . . . . . . . . . . . . . . . . . . 5
     7.1.  Normative References  . . . . . . . . . . . . . . . . . . . 5
     7.2.  Informative References  . . . . . . . . . . . . . . . . . . 5

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RFC 5341          IANA Registry for TEL URI Parameters    September 2008

1.  Introduction

   The tel URI (RFC 3966 [1]), defines a URI that can be used to
   represent resources identified by telephone numbers.  The tel URI,
   like many other URIs, provides extensibility through the definition
   of new URI parameters and new values for existing parameters.
   However, RFC 3966 did not specify an IANA registry where such
   parameters and values can be listed and standardized.  This
   specification creates such a registry.

2.  Terminology

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   document are to be interpreted as described in [2].

3.  Use of the Registry

   The tel URI parameters and values for these parameters MUST be
   documented in a RFC or other permanent and readily available public
   specification in order to be registered by IANA.  This documentation
   MUST fully explain the syntax, intended usage, and semantics of the
   parameter.  The intent of this requirement is to assure
   interoperability between independent implementations, and to prevent
   accidental namespace collisions between implementations of dissimilar

   Documents defining tel URI parameters or parameter values MUST
   register them with IANA, as described in Section 4.  The IANA
   registration policy for such parameters is "Specification Required,
   Designated Expert," and is further discussed in Section 4.2.

   Some tel URI parameters only accept a set of predefined parameter
   values while others can take any value.  There are also parameters
   that do not have any value; they are used as flags.

   Those URI parameters that take on predefined values typically take on
   a large number of values.  Registering each of those values, or
   creating a sub-registry for each such parameter is not appropriate.
   Instead, we have chosen to register URI parameter values by
   reference.  That is, the entry in the URI parameter registry for a
   given URI parameter contains references to the RFCs defining new
   values of that parameter.

   Accordingly, the tel URI parameter registry contains a column that
   indicates whether or not each parameter accepts a value.  The column
   may contain "No value" or "Constrained".  A "Constrained" in the
   column implies that certain predefined values exist for this

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RFC 5341          IANA Registry for TEL URI Parameters    September 2008

   parameter and the accompanying RFC or other permanent and readily
   available public specification should be consulted to find out the
   accepted set of values.  A "No Value" in the column implies that the
   parameter is used either as a flag, or does not have a set of
   predefined values.  The accompanying RFC or other permanent and
   readily available public specification should provide more
   information on the semantics of the parameter.

4.  IANA Considerations

   The specification creates a new IANA registry named "tel URI

4.1.  tel URI Parameters Registry

   New tel URI parameters and new values for existing tel URI parameters
   MUST be registered with IANA.

   When registering a new tel URI parameter, the following information
   MUST be provided:

   o  Name of the parameter.

   o  Whether the parameter only accepts a set of predefined values.

   o  Reference to the RFC or other permanent and readily available
      public specification defining the parameter and new values.

   When registering a new value for an existing tel URI parameter, the
   following information MUST be provided:

   o  Name of the parameter.

   o  Reference to the RFC or other permanent and readily available
      public specification providing the new value.

   Table 1 contains the initial values for this registry.

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RFC 5341          IANA Registry for TEL URI Parameters    September 2008

   Parameter Name     Predefined Values     Reference
   --------------     -----------------     ---------
   isub               Constrained           [RFC3966]
   isub-encoding      Constrained           [RFC4715]
   ext                Constrained           [RFC3966]
   phone-context      Constrained           [RFC3966]
   enumdi             No value              [RFC4759]
   npdi               No value              [RFC4694]
   rn                 Constrained           [RFC4694]
   rn-context         Constrained           [RFC4694]
   cic                Constrained           [RFC4694]
   cic-context        Constrained           [RFC4694]
   tgrp               Constrained           [RFC4904]
   trunk-context      Constrained           [RFC4904]

   Table 1: IANA tel URI parameter registry

4.2.  Registration Policy for tel URI Parameters

   As per the terminology in [3] and actions accorded to such a role,
   the registration policy for tel URI parameters shall be
   "Specification Required, Designated Expert" (the former implicitly
   implies the latter).

   The Designated Expert, when deliberating on whether to include a new
   parameter in the tel URI registry, may use the criteria provided
   below to reach a decision (this is not an exhaustive list but
   representative of the issues to consider when rendering an equitable

   o  If the tel URI -- with the parameter under consideration -- will
      be converted to a URI used by other signaling protocols such as
      the Session Initiation Protocol (SIP [5]) or H.323 [7], then the
      expert must consider whether this parameter merely encapsulates
      signaling information that is not meaningful to the processing of
      requests in the domain of the converted URI.  For example, certain
      Integrated Services Digital Network (ISDN) User Part (ISUP, [8])
      parameters have no equivalent corollary in SIP; thus, their
      presence or absence in a SIP URI will not hinder the normal rules
      for processing that URI.  Other parameters may affect the normal
      processing rules associated with the URI; in such cases, the
      expert must carefully consider the ramifications, if any, of the
      presence of such parameters.

   o  Certain parameters of a tel URI can be optional.  These parameters
      act as metadata about the identifier in the tel URI.  Optional
      parameters should provide additional information to a service for
      which they apply instead of acting as enablers of that service in

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RFC 5341          IANA Registry for TEL URI Parameters    September 2008

      the first place.  The service must continue to be invoked and
      operate normally even in the absence of these parameters.

5.  Security Considerations

   The registry in this document does not in itself have security
   considerations.  However, as mentioned in [4], an important reason
   for the IETF to manage the extensions of SIP is to ensure that all
   extensions and parameters are able to provide secure usage.  The
   supporting RFC publications for parameter registrations described in
   this specification MUST provide detailed security considerations for

6.  Acknowledgments

   The structure of this document comes from [6], which is the
   equivalent work done in the SIP domain to establish a registry.  Ted
   Hardie, Alfred Hoenes, Jon Peterson, and Jonathan Rosenberg provided
   substantive comments that have improved this document.

   Brian Carpenter, Lars Eggert, Pasi Eronen, Chris Newman, and Glen
   Zorn provided feedback during IESG review and Gen-ART review.

7.  References

7.1.  Normative References

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

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

   [3]  Narten, T. and H. Alvestrand, "Guidelines for Writing an IANA
        Considerations Section in RFCs", BCP 26, RFC 5226, May 2008.

7.2.  Informative References

   [4]  Mankin, A., Bradner, S., Mahy, R., Willis, D., Ott, J., and B.
        Rosen, "Change Process for the Session Initiation Protocol
        (SIP)", BCP 67, RFC 3427, December 2002.

   [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.

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RFC 5341          IANA Registry for TEL URI Parameters    September 2008

   [6]  Camarillo, G., "The Internet Assigned Number Authority (IANA)
        Uniform Resource Identifier (URI) Parameter Registry for the
        Session Initiation Protocol (SIP)", BCP 99, RFC 3969,
        December 2004.

   [7]  ITU-T H.323, "H.323: Packet-based multimedia communications
        systems", June 2006.

   [8]  ITU-T Q.764, "Signaling System No. 7: ISDN User Part Signaling
        Procedures", December 1999.

Authors' Addresses

   Cullen Jennings
   Cisco Systems
   170 West Tasman Drive
   Mailstop SJC-21/2
   San Jose, CA  95134

   Phone:  +1 408 902-3341
   EMail:  fluffy@cisco.com

   Vijay K. Gurbani
   Bell Laboratories, Alcatel-Lucent
   2701 Lucent Lane
   Room 9F-546
   Lisle, IL  60532

   Phone:  +1 630 224-0216
   EMail:  vkg@alcatel-lucent.com

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RFC 5341          IANA Registry for TEL URI Parameters    September 2008

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